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Analytical chemistry Analytical chemistry is the study of the separation , identification, and quantification of the chemical components of natural and artificialmaterials . Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of one or more of these components. The separation of components is often performed prior to analysis. Analytical methods can be separated into classical and instrumental. Classical methods (also known as wet chemistry methods) use separations such as precipitation , extraction , and distillation and qualitative analysis by color, odor, or melting point. Quantitative analysis is achieved by measurement of weight or volume. Instrumental methods use an apparatus to measure physical quantities of the analyte such aslight absorption , fluorescence , or conductivity . The separation of materials is accomplished using chromatography or electrophoresis methods. Analytical chemistry is also focused on improvements in experimental design , chemometrics , and the creation of new measurement tools to provide better chemical information. Analytical chemistry has applications in forensics , bioanalysis , clinical analysis, environmental analysis , and materials analysis . History

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Analytical chemistryAnalytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificialmaterials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of one or more of these components. The separation of components is often performed prior to analysis. Analytical methods can be separated into classical and instrumental. Classical methods (also known as wet chemistry methods) use separations such as precipitation, extraction, and distillation and qualitative analysis by color, odor, or melting point. Quantitative analysis is achieved by measurement of weight or volume. Instrumental methods use an apparatus to measure physical quantities of the analyte such aslight absorption, fluorescence, or conductivity. The separation of materials is accomplished using chromatography or electrophoresismethods. Analytical chemistry is also focused on improvements in experimental design, chemometrics, and the creation of new measurement tools to provide better chemical information. Analytical chemistry has applications in forensics, bioanalysis, clinical analysis, environmental analysis, and materials analysis.

History

Gustav Kirchhoff (left) and Robert Bunsen (right)

Analytical chemistry has been important since the early days of chemistry, providing methods for determining which elements and chemicals are present in the world around us. During this period significant analytical contributions to chemistry include the development of systematic elemental analysis by Justus von Liebig and systematized organic analysis based on the specific reactions of functional groups. The first instrumental analysis was flame emissive spectrometry developed by Robert Bunsen andGustav Kirchhoff who discovered rubidium (Rb) and caesium (Cs) in 1860. Most of the major developments in analytical chemistry take place after 1900. During this period instrumental analysis becomes progressively dominant in the field. In particular many of the basic spectroscopic and spectrometric techniques were discovered in the early 20th century and refined in the late 20th century. The separation sciences follow a similar time line of development and also become increasingly transformed into high performance instruments. In the 1970s many of these techniques began to be used together to achieve a complete characterization of samples. Starting in approximately the 1970s into the present day analytical chemistry has progressively become more inclusive of biological questions (bioanalytical chemistry), whereas it had previously been largely focused on inorganic or small organic molecules. Lasers have been increasingly used in chemistry as probes and even to start and influence a wide variety of reactions. The late 20th century also saw an expansion of the application of analytical chemistry from somewhat academic chemical questions to forensic, environmental, industrial and medical questions, such as in histology. Modern analytical chemistry is dominated by instrumental analysis. Many analytical chemists focus on a single type of instrument. Academics tend to either focus on new applications and discoveries or on new methods of analysis. The discovery of a chemical present in blood that increases the risk of cancer would be a discovery that an analytical chemist might be involved in. An effort to develop a new method might involve the use of a tunable laser to increase the specificity and sensitivity of a spectrometric method. Many methods, once developed, are kept purposely static so that data can be compared over long periods of time. This is particularly true in industrial quality assurance (QA), forensic and environmental applications. Analytical chemistry plays an increasingly important role in the pharmaceutical industry where, aside from QA, it is used in discovery of new drug candidates and in clinical applications where understanding the interactions between the drug and the patient are critical.

Classical methods

The presence of copper in this qualitative analysis is indicated by the bluish-green color of the flame.

Although modern analytical chemistry is dominated by sophisticated instrumentation, the roots of analytical chemistry and some of the principles used in modern instruments are from traditional techniques many of which are still used today. These techniques also tend to form the backbone of most undergraduate analytical chemistry educational labs.

Qualitative analysisA qualitative analysis determines the presence or absence of a particular compound, but not the mass or concentration. That is it is not related to quantity.

Chemical testsThere are numerous qualitative chemical tests, for example, the acid test for gold and the Kastle-Meyer test for the presence of blood.

Flame testInorganic qualitative analysis generally refers to a systematic scheme to confirm the presence of certain, usually aqueous, ions or elements by performing a series of reactions that eliminate ranges of possibilities and then confirms suspected ions with a confirming test. Sometimes small carbon containing ions are included in such schemes. With modern instrumentation these tests are rarely used but can be useful for educational purposes and in field work or other situations where access to state-of-theart instruments are not available or expedient.

Gravimetric analysisGravimetric analysis involves determining the amount of material present by weighing the sample before and/or after some transformation. A common example used in undergraduate education is the determination of the amount of water in a hydrate by heating the sample to remove the water such that the difference in weight is due to the water loss of water.

Volumetric analysisTitration involves the addition of a reactant to a solution being analyzed until some equivalence point is reached. Often the amount of material in the solution being analyzed may be determined. Most familiar to those who have taken college chemistry is the acid-base titration involving a color changing indicator. There are many other types of titrations, for example potentiometric titrations. These titrations may use different types of indicators to reach some equivalence point.

Instrumental methods

Block diagram of an analytical instrument showing the stimulus and measurement of response

SpectroscopySpectroscopy measures the interaction of the molecules with electromagnetic radiation. Spectroscopy consists of many different applications such as atomic absorption spectroscopy, atomic emission spectroscopy, ultraviolet-visible spectroscopy, x-ray fluorescence spectroscopy, infrared spectroscopy, Raman spectroscopy, dual polarisation interferometry, nuclear magnetic resonance spectroscopy, photoemission spectroscopy, Mssbauer spectroscopy and so on.

Mass spectrometry.

An accelerator mass spectrometerused for radiocarbon dating and other analysis.

Mass spectrometry measures mass-to-charge ratio of molecules using electric and magnetic fields. There are several ionization methods: electron impact, chemical ionization, electrospray, fast atom bombardment, matrix assisted laser desorption ionization, and others. Also, mass spectrometry is categorized by approaches of mass analyzers: magnetic-sector, quadrupole mass analyzer,quadrupole ion trap, time-of-flight, Fourier transform ion cyclotron resonance, and so on.

CrystallographyCrystallography is a technique that characterizes the chemical structure of materials at the atomic level by analyzing the diffraction patterns of usually x-rays that have been deflected by atoms in the material. From the raw data the relative placement of atoms in space may be determined.

Electrochemical analysisElectroanalytical methods measure the potential (volts) and/or current (amps) in an electrochemical cell containing the analyte. These methods can be categorized according to which aspects of the cell are controlled and which are measured. The three main categories arepotentiometry (the difference in electrode potentials is measured), coulometry (the cell's current is measured over time), and voltammetry (the cell's current is measured while actively altering the cell's potential).

Thermal analysisCalorimetry and thermogravimetric analysis measure the interaction of a material and heat.

Separation

Separation of black ink on a thin layer chromatography plate.

Separation processes are used to decrease the complexity of material mixtures. Chromatography andelectrophoresis are representative of this field.

Hybrid techniquesCombinations of the above techniques produce a "hybrid" or "hyphenated" technique.[9] [10][11][12][13] Several examples are in popular use today and new hybrid techniques are under development. For example, gas chromatography-mass spectrometry, gas chromatography-infrared spectroscopy, liquid chromatography-mass spectrometry, liquid chromatography-NMR spectroscopy. liquid chromagraphy-infrared spectroscopy and capillary electrophoresis-mass spectrometry. Hyphenated separation techniques refers to a combination of two (or more) techniques to detect and separate chemicals from solutions. Most often the other technique is some form of chromatography. Hyphenated techniques are widely used in chemistry and biochemistry. A slash is sometimes used instead of hyphen, especially if the name of one of the methods contains a hyphen itself.

Microscopy

Fluorescence microscope image of two mouse cell nuclei in prophase(scale bar is 5 m).

The visualization of single molecules, single cells, biological tissues and nanomaterials is an important and attractive approach in analytical science. Also, hybridization with other traditional analytical tools is revolutionizing analytical science. Microscopy can be categorized into three different fields: optical microscopy, electron microscopy, and scanning probe microscopy. Recently, this field is rapidly progressing because of the rapid development of the computer and camera industries.

Lab-on-a-chip

A glass microreactor

Devices that integrate (multiple) laboratory functions on a single chip of only millimeters to a few square centimeters in size and that are capable of handling extremely small fluid volumes down to less than pico liters.

StandardsStandard curve

A calibration curve plot showing limit of detection (LOD), limit of quantification(LOQ), dynamic range, and limit of linearity (LOL).

A general method for analysis of concentration involves the creation of a calibration curve. This allows for determination of the amount of a chemical in a material by

comparing the results of unknown sample to those of a series known standards. If the concentration of element or compound in a sample is too high for the detection range of the technique, it can simply be diluted in a pure solvent. If the amount in the sample is below an instrument's range of measurement, the method of addition can be used. In this method a known quantity of the element or compound under study is added, and the difference between the concentration added, and the concentration observed is the amount actually in the sample.

Internal standardsSometimes an internal standard is added at a known concentration directly to an analytical sample to aid in quantitation. The amount of analyte present is then determined relative to the internal standard as a calibrant.

Standard additionThe method of standard addition is used in instrumental analysis to determine concentration of a substance (analyte) in an unknown sample by comparison to a set of samples of known concentration, similar to using a calibration curve. Standard addition can be applied to most analytical techniques and is used instead of a calibration curve to solve the matrix effect problem.

Signals and noiseOne of the most important components of analytical chemistry is maximizing the desired signal while minimizing the associated noise.[15]The analytical figure of merit is known as the signal-to-noise ratio (S/N or SNR). Noise can arise from environmental factors as well as from fundamental physical processes.

Thermal noiseThermal noise results from the motion of charge carriers (usually electrons) in an electrical circuit generated by their thermal motion. Thermal noise is white noise meaning that the power spectral density is constant throughout the frequency spectrum. The root mean square value of the thermal noise in a resistor is given by[15]

where kB is Boltzmann's constant, T is the temperature, R is the resistance, and f is the bandwidth of the frequency f.

Shot noiseMain article: Shot noise Shot noise is a type of electronic noise that occurs when the finite number of particles (such as electrons in an electronic circuit or photonsin an optical device) is small enough to give rise to statistical fluctuations in a signal. Shot noise is a Poisson process and the charge carriers that make up the current follow a Poisson distribution. The root mean square current fluctuation is given by[15]

where e is the elementary charge and I is the average current. Shot noise is white noise.

Flicker noiseFlicker noise is electronic noise with a 1/ frequency spectrum; as f increases, the noise decreases. Flicker noise arises from a variety of sources, such as impurities in a conductive channel, generation and recombination noise in a transistor due to base current, and so on. This noise can be avoided by modulation of the signal at a higher frequency, for example through the use of a lock-in amplifier.

Environmental noise

Noise in a thermogravimetric analysis; lower noise in the middle of the plot results from less human activity (and environmental noise) at night.

Environmental noise arises from the surroundings of the analytical instrument. Sources of electromagnetic noise are power lines, radio and television stations, wireless devices and electric motors. Many of these noise sources

are narrow bandwidth and therefore can be avoided. Temperature and vibration isolation may be required for some instruments.

Noise reductionNoise reduction can be accomplished either in hardware or software. Examples of hardware noise reduction are the use of shielded cable, analog filtering, and signal modulation. Examples of software noise reduction are digital filtering, ensemble average, boxcar average, and correlation methods.

ApplicationsAnalytical chemistry research is largely driven by performance (sensitivity, selectivity, robustness, linear range, accuracy, precision, and speed), and cost (purchase, operation, training, time, and space). Among the main branches of contemporary analytical atomic spectrometry, the most widespread and universal are optical and mass spectrometry. In the direct elemental analysis of solid samples, the new leaders are laser-induced breakdown and laser ablation mass spectrometry, and the related techniques with transfer of the laser ablation products into inductively coupled plasma. Advances in design of diode lasers and optical parametric oscillators promote developments in fluorescence and ionization spectrometry and also in absorption techniques where uses of optical cavities for increased effective absorption pathlength are expected to expand. Steady progress and growth in applications of plasmaand laser-based methods are noticeable. An interest towards the absolute (standardless) analysis has revived, particularly in the emission spectrometry. A lot of effort is put in shrinking the analysis techniques to chip size. Although there are few examples of such systems competitive with traditional analysis techniques, potential advantages include size/portability, speed, and cost. (micro Total Analysis System (TAS) or Lab-on-a-chip). Microscale chemistry reduces the amounts of chemicals used. Much effort is also put into analyzing biological systems. Examples of rapidly expanding fields in this area are:

Genomics

- DNA sequencing and its related research. Genetic fingerprinting and DNA microarray are very popular tools and research fields. Proteomics

- the analysis of protein concentrations and modifications, especially in response to various stressors, at various developmental stages, or in various parts of the body. Metabolomics

- similar to proteomics, but dealing with metabolites. - mRNA and its associated field

Transcriptomics Lipidomics

- lipids and its associated field - peptides and its associated field

Peptidomics Metalomics

- similar to proteomics and metabolomics, but dealing with metal concentrations and especially with their binding to proteins and other molecules. Analytical chemistry has played critical roles in the understanding of basic science to a variety of practical applications, such as biomedical applications, environmental monitoring, quality control of industrial manufacturing, forensic science and so on. The recent developments of computer automation and information technologies have innervated analytical chemistry to initiate a number of new biological fields. For example, automated DNA sequencing machines were the basis to complete human genome projects leading to the birth of genomics. Protein identification and peptide sequencing by mass spectrometry opened a new field of proteomics. Furthermore, a number of ~omics based on analytical chemistry have become important areas in modern biology. Also, analytical chemistry has been an indispensable area in the development of nanotechnology. Surface characterization instruments,electron microscopes and scanning probe microscopes enables scientists to visualize atomic structures with chemical characterizations. Among active contemporary analytical chemistry research fields, micro total analysis system is considered as a great promise of revolutionary technology. In this approach, integrated and miniaturized analytical systems are being developed to control and analyze single cells and single molecules. This

cutting-edge technology has a promising potential of leading a new revolution in science as integrated circuits did in computer developments. Sensory Analysis And Instruments

Sensory analysis is a method used to describe the sensations that humans perceive with their 5 senses when in contact with a product. Among the 5 senses, we distinguish physical (hearing, touch, sight) and chemical (olfaction, taste) senses. Alpha MOS has developed solutions linked to chemical senses. The sense of smell, also called olfaction, is the perception of odorant molecules either by direct inhalation or during mastication (retro nasal way). The sense of taste consists of the perception of savors that are the sensations perceived by the tongue during tasting. Commonly, savors are classified in 5 categories: salt, sour, bitter, sweet, umami In sensory analysis, there exist 2 types of tests: hedonic tests (I like it / I don't like it) which consist of consumer tests analytical tests (descriptive or discriminative) that are conducted by a trained sensory panel.

For analytical tests, Electronic nose and tongue analyzers can also be used. These instruments have the specificity to analyze odor / taste in the same way as human nose and tongue: instead of separating and identifying the various chemical compounds, they measure a global odor / taste.

LIST OF ELECTRONIC DEVICES USED IN CHEMICAL ANALYSIS AND MEASUREMENTS

BreathalyzerFrom Wikipedia, the free encyclopedia Jump to: navigation, search

A law enforcement grade breathalyzer

A breathalyzer (U.S.A.) or breathalyser (U.K.) (a portmanteau of breath and analyzer/analyser) is a device for estimating blood alcohol content (BAC) from a breath sample. Breathalyzer is the brand name of a series of models made by one manufacturer of these instruments (originally Smith and Wesson[1], later sold to National Draeger), but has become a genericized trademark for all such instruments.[citation needed] In Canada, a preliminary nonevidentiary screening device can be approved by Parliament as an approved screening device, and an evidentiary breath instrument can be similarly designated as an approved instrument. The U.S. National Highway Traffic Safety Administration maintains a Conforming Products List of breath alcohol devices approved for evidentiary use,[2] as well as for preliminary screening use.[3]

Contents[hide]

1 2 3 4 5 6

Origins Chemistry Law enforcement Consumer use Breath test evidence in the United States Common sources of error o 6.1 Calibration o 6.2 Non-specific analysis o 6.3 Interfering compounds o 6.4 Homeostatic variables o 6.5 Mouth alcohol o 6.6 Testing during absorptive phase o 6.7 Retrograde extrapolation 7 Photovoltaic assay 8 Breathalyzer myths 9 Products that interfere with testing 10 References

11 External links

[edit] OriginsA 1927 paper produced by Emil Bogen[4], who collected air in a football and then tested this air for traces of alcohol, discovered that the alcohol content of 2 litres of expired air was a little greater than that of 1 cc of urine. However, research into the possibilities of using breath to test for alcohol in a person's body dates as far back as 1874, when Anstie made the observation that small amounts of alcohol were excreted in breath[5]. The first practical roadside breath-testing device intended for use by the police was the drunkometer. The drunkometer was developed by Professor Harger in 1938. The drunkometer collected a motorist's breath sample directly into a balloon inside the machine. The breath sample was then pumped through an acidified potassium permanganate solution. If there was alcohol in the breath sample, the solution changed colour. The greater the colour change, the more alcohol there was present in the breath. The drunkometer was quite cumbersome and was approximately the size of a shoe box. It was more reminiscent of a portable laboratory. In late 1927, in a case in Marlborough, England, a Dr. Gorsky, Police Surgeon, asked a suspect to inflate a football bladder with his breath. Since the 2 liters of the man's breath contained 1.5 ml of ethanol[dubious discuss], Dr. Gorsky testified before the court that the defendant was "50% drunk".[6] Though technologies for detecting alcohol vary, it is widely accepted that Dr. Robert Borkenstein (19122002), a captain with the Indiana State Police and later a professor at Indiana University at Bloomington, is regarded as the first to create a device that measures a subject's blood alcohol level based on a breath sample. In 1954, Borkenstein invented his breathalyzer, which used chemical oxidation and photometry to determine alcohol concentration. Subsequent breathalyzers have converted primarily to infrared spectroscopy. The invention of the breathalyzer provided law enforcement with a non-invasive test providing immediate results to determine an individual's breath alcohol concentration at the time of testing. Also, the breath alcohol concentration test result itself can vary between individuals consuming identical amounts of alcohol due to gender, weight, and genetic pre-disposition.

[edit] ChemistryWhen the user exhales into the breathalyzer, any ethanol present in their breath is oxidized to acetic acid at the anode: CH3CH2OH(g) + H2O(l) -> CH3CO2H(l) + 4H+(aq) + 4eAt the cathode, atmospheric oxygen is reduced: O2(g) + 4H+(aq) + 4e- -> 2H2O(l)

The overall reaction, then, is the oxidation of ethanol to acetic acid and water. CH3CH2OH(l) + O2(g) -> CH3COOH(l) + H2O(l) The electrical current produced by this reaction is measured, processed, and displayed as an approximation of overall blood alcohol content by the breathalyzer.

[edit] Law enforcementBreath analyzers do not directly measure blood alcohol content or concentration, which requires the analysis of a blood sample. Instead, they estimate BAC indirectly by measuring the amount of alcohol in one's breath. Two breathalyzer technologies are most prevalent. Desktop analyzers generally use infrared spectrophotometer technology, electrochemical fuel cell technology, or a combination of the two. Hand-held field testing devices are generally based on electrochemical platinum fuel cell analysis and, depending upon jurisdiction, may be used by officers in the field as a form of "field sobriety test" commonly called PBT (preliminary breath test) or PAS (preliminary alcohol screening) or as evidential devices in POA (point of arrest) testing.

[edit] Consumer useThere are many models of consumer or personal breath alcohol testers on the market. These hand-held devices are generally less expensive than the devices used by law enforcement. Most retail consumer breath testers use semiconductor-based sensing technology, which is less expensive, less accurate, and less reliable than fuel cell and infrared devices. While semiconductor devices can sense the presence of breath alcohol, they do not provide as reliable measures of BAC. All breath alcohol testers sold to consumers in the United States are required to be certified by the Food and Drug Administration[7], while those used by law enforcement must be approved by the Department of Transportation's National Highway Traffic Safety Administration.[8] Manufacturers of over-the-counter consumer breathalyzers must submit an FDA 510(k) Premarket Clearance to demonstrate that the device to be marketed is at least as safe and effective, that is, substantially equivalent, to a legally marketed device (21 CFR 807.92(a) (3)) that is not subject to Premarket Approval (PMA). Submitters must compare their device to one or more similar legally marketed devices and make and support their substantial equivalency claims.[9] The devices are cleared as "screeners" which means they have met the requirements used by the FDA for detecting the presence of alcohol in the breath. Screener certification does not mean that the device can measure breath alcohol content accurately. Many breathalyzers cleared by the FDA are very innaccurate when it comes to BAC measurement. No semiconductor device has ever been approved for evidential use (to stand-up in a court of law) by any State Law Enforcement Agencies or the U.S. Department of Transportation.

[edit] Breath test evidence in the United States

This section does not cite any references or sources.Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2010)

A breathalyzer in action

The breath alcohol content reading is used in criminal prosecutions in two ways. The operator of a vehicle whose reading indicates a BrAC over the legal limit for driving will be charged with having committed an illegal per se offense: that is, it is automatically illegal throughout the United States to drive a vehicle with a BrAC of 0.08 or higher. One exception is the State of Wisconsin, where a first time drunk driving offense is normally a civil ordinance violation.[10] The breathalyzer reading will be offered as evidence of that crime, although the issue is what the BrAC was at the time of driving rather than at the time of the test. Some jurisdictions now allow the use of breathalyzer test results without regard as to how much time passed between operation of the vehicle and the time the test was administered.[citation needed] The suspect will also be charged with driving under the influence of alcohol (sometimes referred to as driving or operating while intoxicated). While BrAC tests are not necessary to prove a defendant was under the influence, laws in most states require the jury to presume that he was under the influence if his BrAC is found and believed to be over 0.08 (grams of alcohol/210 liters breath) when driving.[citation needed] This is a rebuttable presumption, however: the jury can disregard the test if they find it unreliable or if other evidence establishes a reasonable doubt. Infrared instruments are also known as "evidentiary breath testers" and generally produce courtadmissible results.[citation needed] Other instruments, usually hand held in design, are known as "preliminary breath testers" (PBT), and their results, while valuable to an officer attempting to establish probable cause for a drunk driving arrest, are generally not admissible in court. Some states, such as Idaho, permit data or "readings" from hand-held PBTs to be presented as evidence in court. If at all, they are generally only admissible to show the presence of alcohol or as a passfail field sobriety test to help determine probable cause to arrest. South Dakota does not permit data from any type of breath tester, and relies entirely on blood tests to ensure accuracy.

[edit] Common sources of error

An editor has expressed a concern that this section lends undue weight to certain ideas, incidents, controversies or matters relative to the article subject as a whole. Please help to create a more balanced presentation. Discuss and resolve this issue before removing this message.(March 2009)

Breath testers can be very sensitive to temperature, for example, and will give false readings if not adjusted or recalibrated to account for ambient or surrounding air temperatures. The temperature of the subject is also very important.[citation needed] Breathing pattern can also significantly affect breath test results. One study found that the BAC readings of subjects decreased 1114% after running up one flight of stairs and 2225% after doing so twice. Another study found a 15% decrease in BAC readings after vigorous exercise or hyperventilation. Hyperventilation for 20 seconds has been shown to lower the reading by approximately 32%. On the other hand, holding one's breath for 30 seconds can increase the breath test result by about 28%.[citation needed] Some breath analysis machines assume a hematocrit (cell volume of blood) of 47%. However, hematocrit values range from 42 to 52% in men and from 37 to 47% in women. A person with a lower hematocrit will have a falsely high BAC reading. Research indicates that breath tests can vary at least 15% from actual blood alcohol concentration. An estimated 23% of individuals tested will have a BAC reading higher than their true BAC. Police in Victoria, Australia, use breathalyzers that give a recognized 20% tolerance on readings. Noel Ashby, former Victoria Police Assistant Commissioner (Traffic & Transport), claims that this tolerance is to allow for different body types.[11]

[edit] CalibrationMany handheld breathalyzers sold to consumers use a silicon oxide sensor (also called a semiconductor sensor) to determine the blood alcohol concentration. These sensors are far more prone to contamination and interference from other substances besides breath alcohol. The sensors require recalibration or replacement every six months. Higher end personal breathalyzers and professional-use breath alcohol testers use platinum fuel cell sensors.These too require recalibration but at less frequent intervals than semiconductor devices, usually once a year. Calibration is the process of checking and adjusting the internal settings of a breathalyzer by comparing and adjusting its test results to a known alcohol standard. Law enforcement breathalyzers are meticulously maintained and re-calibrated frequently to ensure accuracy. There are two methods of calibrating a precision fuel cell breathalyzer, the Wet Bath and the Dry Gas method. Each method requires specialized equipment and factory trained technicians. It is not a procedure that can be conducted by untrained users or without the proper equipment.

The Dry-Gas Method utilizes a portable calibration standard which is a precise mixture of alcohol and inert nitrogen available in a pressurized canister. Initial equipment costs are less than alternative methods and the steps required are fewer. The equipment is also portable allowing calibrations to be done when and where required. The Wet Bath Method utilizes an alcohol/water standard in a precise specialized alcohol concentration, contained and delivered in specialized simulator equipment. Wet bath apparatus has a higher initial cost and is not intended to be portable. The standard must be fresh and replaced regularly. Some semiconductor models are designed to allow the sensor module to be replaced without the need to send the unit to a calibration lab.[citation needed]

[edit] Non-specific analysisOne major problem with older breathalyzers is non-specificity: the machines not only identify the ethyl alcohol (or ethanol) found in alcoholic beverages, but also other substances similar in molecular structure or reactivity. The oldest breathalyzer models pass breath through a solution of potassium dichromate, which oxidizes ethanol into acetic acid, changing color in the process. A monochromatic light beam is passed through this sample, and a detector records the change in intensity and, hence, the change in color, which is used to calculate the percent alcohol in the breath. However, since potassium dichromate is a strong oxidizer, numerous alcohol groups can be oxidized by it, producing false positives. This source of false positives is unlikely as very few other substances found in exhaled air is oxidisable. Infrared-based breathalyzers project an infrared beam of radiation through the captured breath in the sample chamber and detect the absorbance of the compound as a function of the wavelength of the beam, producing an absorbance spectrum that can be used to identify the compound, as the absorbance is due to the harmonic vibration and stretching of specific bonds in the molecule at specific wavelengths (see infrared spectroscopy). The characteristic bond of alcohols in infrared is the O-H bond, which gives a strong absorbance at a short wavelength. The more light is absorbed by compounds containing the alcohol group, the less reaches the detector on the other sideand the higher the reading. Other groups, most notably aromatic rings and carboxylic acids can give similar absorbance readings.[12] Even water vapour does.

[edit] Interfering compoundsSome natural and volatile interfering compounds do exist, however. For example, the National Highway Traffic Safety Administration (NHTSA) has found that dieters and diabetics may have acetone levels hundreds or even thousand of times higher than those in others. Acetone is one of the many substances that can be falsely identified as ethyl alcohol by some breath machines. However, fuel cell based systems are non-responsive to substances like acetone.

A study in Spain showed that metered-dose inhalers (MDIs) used in asthma treatment are also a cause of false positives in breath machines. Substances in the environment can also lead to false BAC readings. For example, methyl tertbutyl ether (MTBE), a common gasoline additive, has been alleged anecdotally to cause false positives in persons exposed to it. Tests have shown this to be true for older machines; however, newer machines detect this interference and compensate for it.[13] Any number of other products found in the environment or workplace can also cause erroneous BAC results. These include compounds found in lacquer, paint remover, celluloid, gasoline, and cleaning fluids, especially ethers, alcohols, and other volatile compounds.

[edit] Homeostatic variablesBreathalyzers assume that the subject being tested has a 2100-to-1 partition ratio[14] in converting alcohol measured in the breath to estimates of alcohol in the blood. If the instrument estimates the BAC, then it measures weight of alcohol to volume of breath, so it will effectively measure grams of alcohol per 2100 ml of breath given. This measure is in direct proportion to the amount of grams of alcohol to every 100 ml of blood. Therefore, there is a 2100-to-1 ratio of alcohol in blood to alcohol in breath. However, this assumed partition ratio varies from 1300:1 to 3100:1 or wider among individuals and within a given individual over time. Assuming a true (and US legal) blood-alcohol concentration of .07%, for example, a person with a partition ratio of 1500:1 would have a breath test reading of .10%over the legal limit. Most individuals do, in fact, have a 2100-to-1 partition ratio in accordance with William Henry's law, which states that when the water solution of a volatile compound is brought into equilibrium with air, there is a fixed ratio between the concentration of the compound in air and its concentration in water. This ratio is constant at a given temperature. The human body is 37 degrees Celsius on average. Breath leaves the mouth at a temperature of 34 degrees Celsius. Alcohol in the body obeys Henry's Law as it is a volatile compound and diffuses in body water. To ensure that variables such as fever and hypothermia could not be pointed out to influence the results in a way that was harmful to the accused, the instrument is calibrated at a ratio of 2100:1, underestimating by 9 percent. In order for a person running a fever to significantly overestimate, he would have to have a fever that would likely see the subject in the hospital rather than driving in the first place. Studies suggest that about 1.8% of the population have a partition ratio below 2100:1. Thus, a machine using a 2100-to-1 ratio could actually overestimate the BAC. As much as 14% of the population has a partition ratio above 2100, thus causing the machine to underreport the BAC. Further, the assumption that the test subject's partition ratio will be averagethat there will be 2100 parts in the blood for every part in the breathmeans that accurate analysis of a given individual's blood alcohol by measuring breath alcohol is difficult, as the ratio varies considerably. Variance in how much one breathes out can also give false readings, usually low.[15] This is due to biological variance in breath alcohol concentration as a function of the volume of air in the lungs, an example of a factor which interferes with the liquid-gas equilibrium assumed by the

devices. The presence of volatile components is another example of this; mixtures of volatile compounds can be more volatile than their components, which can create artificially high levels of ethanol (or other) vapors relative to the normal biological blood/breath alcohol equilibrium.

[edit] Mouth alcoholOne of the most common causes of falsely high breathalyzer readings is the existence of mouth alcohol. In analyzing a subject's breath sample, the breathalyzer's internal computer is making the assumption that the alcohol in the breath sample came from alveolar airthat is, air exhaled from deep within the lungs. However, alcohol may have come from the mouth, throat or stomach for a number of reasons. To help guard against mouth-alcohol contamination, certified breathtest operators are trained to observe a test subject carefully for at least 1520 minutes before administering the test. The problem with mouth alcohol being analyzed by the breathalyzer is that it was not absorbed through the stomach and intestines and passed through the blood to the lungs. In other words, the machine's computer is mistakenly applying the partition ratio (see above) and multiplying the result. Consequently, a very tiny amount of alcohol from the mouth, throat or stomach can have a significant impact on the breath-alcohol reading. Other than recent drinking, the most common source of mouth alcohol is from belching or burping. This causes the liquids and/or gases from the stomachincluding any alcoholto rise up into the soft tissue of the esophagus and oral cavity, where it will stay until it has dissipated. The American Medical Association concludes in its Manual for Chemical Tests for Intoxication (1959): "True reactions with alcohol in expired breath from sources other than the alveolar air (eructation, regurgitation, vomiting) will, of course, vitiate the breath alcohol results." For this reason, police officers are supposed to keep a DUI suspect under observation for at least 15 minutes prior to administering a breath test. Instruments such as the Intoxilyzer 5000 also feature a "slope" parameter. This parameter detects any decrease in alcohol concentration of 0.006 g per 210 L of breath in 0.6 second, a condition indicative of residual mouth alcohol, and will result in an "invalid sample" warning to the operator, notifying the operator of the presence of the residual mouth alcohol. PBT's, however, feature no such safeguard. Acid reflux, or gastroesophageal reflux disease, can greatly exacerbate the mouth-alcohol problem. The stomach is normally separated from the throat by a valve, but when this valve becomes herniated, there is nothing to stop the liquid contents in the stomach from rising and permeating the esophagus and mouth. The contentsincluding any alcoholare then later exhaled into the breathalyzer.[16] Mouth alcohol can also be created in other ways. Dentures, for example, will trap alcohol. Periodental disease can also create pockets in the gums which will contain the alcohol for longer periods. Also known to produce false results due to residual alcohol in the mouth is passionate kissing with an intoxicated person. Recent use of mouthwash or breath freshenerpossibly to disguise the smell of alcohol when being pulled over by policecontain fairly high levels of alcohol.

[edit] Testing during absorptive phaseAbsorption of alcohol continues for anywhere from 20 minutes (on an empty stomach) to twoand-one-half hours (on a full stomach) after the last consumption. Peak absorption generally occurs within an hour. During the initial absorptive phase, the distribution of alcohol throughout the body is not uniform. Uniformity of distribution, called equilibrium, occurs just as absorption completes. In other words, some parts of the body will have a higher blood alcohol content (BAC) than others. One aspect of the non-uniformity before absorption is complete is that the BAC in arterial blood will be higher than in venous blood. Laws generally require blood samples to be venous. During the initial absorption phase, arterial blood alcohol concentrations are higher than venous. After absorption, venous blood is higher. This is especially true with bolus dosing. With additional doses of alcohol, the body can reach a sustained equilibrium when absorption and elimination are proportional, calculating a general absorption rate of 0.02/drink and a general elimination rate of 0.015/hour. (One drink is equal to 1.5 ounces of liquor, 12 ounces of beer, or 5 ounces of wine [1].) Breath alcohol is a representation of the equilibrium of alcohol concentration as the blood gases (alcohol) pass from the (arterial) blood into the lungs to be expired in the breath. The venous blood picks up oxygen for distribution throughout the body. Breath alcohol concentrations are generally lower than blood alcohol concentrations, because a true representation of blood alcohol concentration is only possible if the lungs were able to completely deflate. Vitreous (eye) fluid provides the most accurate account of blood alcohol concentrations.

[edit] Retrograde extrapolationThe breathalyzer test is usually administered at a police station, commonly an hour or more after the arrest. Although this gives the BrAC at the time of the test, it does not by itself answer the question of what it was at the time of driving. The prosecution typically provides an estimated alcohol concentration at the time of driving utilizing retrograde extrapolation, presented by expert opinion. This involves projecting back in time to estimate the BrAC level at the time of driving, by applying the physiological properties of absorption and elimination rates in the human body. Extrapolation is calculated using five factors and a general elimination rate of 0.015/hour. For example: Time of breath test-10:00pm...Result of breath test-0.080...Time of driving-9:00pm (stopped by officer)...Time of last drink-8:00pm...Last food-12:00pm Using these facts, an expert can say the person's last drink was consumed on an empty stomach, which means absorption of the last drink (at 8:00) was complete within one hour-9:00. At the time of the stop, the driver is fully absorbed. The test result of 0.080 was at 10:00. So the one hour of elimination that has occurred since the stop is added in, making 0.080+0.015=0.095 the approximate breath alcohol concentration at the time of the stop.

[edit] Photovoltaic assayThe photovoltaic assay, used only in the dated Photo Electric Intoximeter (PEI), is a form of breath testing rarely encountered today. The process works by using photocells to analyze the color change of a redox (oxidation-reduction) reaction. A breath sample is bubbled through an aqueous solution of sulfuric acid, potassium dichromate, and silver nitrate. The silver nitrate acts as a catalyst, allowing the alcohol to be oxidized at an appreciable rate. The requisite acidic condition needed for the reaction might also be provided by the sulfuric acid. In solution, ethanol reacts with the potassium dichromate, reducing the dichromate ion to the chromium (III) ion. This reduction results in a change of the solution's colour from red-orange to green. The reacted solution is compared to a vial of non-reacted solution by a photocell, which creates an electric current proportional to the degree of the colour change; this current moves the needle that indicates BAC. Like other methods, breath testing devices using chemical analysis are somewhat prone to false readings. Compounds that have compositions similar to ethanol, for example, could also act as reducing agents, creating the necessary color change to indicate increased BAC.

[edit] Breathalyzer mythsThere are a number of substances or techniques that can supposedly "fool" a breathalyzer (i.e., generate a lower blood alcohol content). A 2003 episode of the popular science television show MythBusters tested a number of methods that supposedly allow a person to fool a breathalyzer test. The methods tested included breath mints, onions, denture cream, mouthwash, pennies and batteries; all of these methods proved ineffective. The show noted that using items such as breath mints, onions, denture cream and mouthwash to cover the smell of alcohol may fool a person, but, since they will not actually reduce a person's BAC, there will be no effect on a breathalyzer test regardless of the quantity used. Pennies supposedly produce a chemical reaction, while batteries supposedly create an electrical charge, yet neither of these methods affected the breathalyzer results.[17] The Mythbusters episode also pointed out another complication: It would be necessary to insert the item into one's mouth (e.g. eat an onion, rinse with mouthwash, conceal a battery), take the breath test, and then possibly remove the item all of which would have to be accomplished discreetly enough to avoid alerting the police officers administering the test (who would obviously become very suspicious if they noticed that a person was inserting items into their mouth prior to taking a breath test). It would likely be very difficult, especially for someone in an intoxicated state, to be able to accomplish such a feat.[17] In addition, the show noted that breath tests are often verified with blood tests (which are more accurate) and that even if a person somehow managed to fool a breath test, a blood test would certainly confirm a person's guilt.[17]

Other substances that might reduce the BAC reading include a bag of activated charcoal concealed in the mouth (to absorb alcohol vapor), an oxidizing gas (such as N2O, Cl2, O3, etc.) that would fool a fuel cell type detector, or an organic interferent to fool an infrared absorption detector. The infrared absorption detector is more vulnerable to interference than a laboratory instrument measuring a continuous absorption spectrum since it only makes measurements at particular discrete wavelengths. However, due to the fact that any interference can only cause higher absorption, not lower, the estimated blood alcohol content will be overestimated.[citation needed] Additionally, Cl2 is rather toxic and corrosive. A 2007 episode of the Spike network's show Manswers showed some of the more common and not-so-common ways of attempts to beat the breathalyzer, none of which work. Test 1 was to suck on a copper coin. (Actually, copper coins are now generally often only copper-coated and mostly zinc or steel.[citation needed]) Test 2 was to hold a battery on the tongue. Test 3 was to chew gum. None of these tests showed a "pass" reading if the subject had consumed alcohol.

[edit] Products that interfere with testingOn the other hand, products such as mouthwash or breath spray can "fool" breath machines by significantly raising test results. Listerine mouthwash, for example, contains 27% alcohol. The breath machine is calibrated with the assumption that the alcohol is coming from alcohol in the blood diffusing into the lung rather than directly from the mouth, so it applies a partition ratio of 2100:1 in computing blood alcohol concentrationresulting in a false high test reading. To counter this, officers are not supposed to administer a PBT for 15 minutes after the subject eats, vomits, or puts anything in their mouth. In addition, most instruments require that the individual be tested twice at least two minutes apart. Mouthwash or other mouth alcohol will have somewhat dissipated after two minutes and cause the second reading to disagree with the first, requiring a retest. (Also see the discussion of the "slope parameter" of the Intoxilyzer 5000 in the "Mouth Alcohol" section above.) This was clearly illustrated in a study conducted with Listerine mouthwash on a breath machine and reported in an article entitled "Field Sobriety Testing: Intoxilyzers and Listerine Antiseptic" published in the July 1985 issue of The Police Chief (p. 70). Seven individuals were tested at a police station, with readings of 0.00%. Each then rinsed his mouth with 20 milliliters of Listerine mouthwash for 30 seconds in accordance with directions on the label. All seven were then tested on the machine at intervals of one, three, five and ten minutes. The results indicated an average reading of 0.43 blood-alcohol concentration, indicating a level that, if accurate, approaches lethal proportions. After three minutes, the average level was still 0.020, despite the absence of any alcohol in the system. Even after five minutes, the average level was 0.011. In another study, reported in 8(22) Drinking/Driving Law Letter 1, a scientist tested the effects of Binaca breath spray on an Intoxilyzer 5000. He performed 23 tests with subjects who sprayed their throats and obtained readings as high as 0.81far beyond lethal levels. The scientist also noted that the effects of the spray did not fall below detectable levels until after 18 minutes.

Carbon dioxide sensor

From Wikipedia, the free encyclopedia Jump to: navigation, search

A carbon dioxide sensor or CO2 sensor is an instrument for the measurement of carbon dioxide gas. The most common principles for CO2 sensors are infrared gas sensors (NDIR) and chemical gas sensors. Measuring carbon dioxide is important in monitoring Indoor air quality and many industrial processes.

Contents[hide]

1 Nondispersive Infrared (NDIR) CO2 Sensors 2 Chemical CO2 Sensors 3 Applications 4 See also 5 References

[edit] Nondispersive Infrared (NDIR) CO2 SensorsNDIR sensors are spectroscopic sensors to detect CO2 in a gaseous environment by its characteristic absorption. The key components are an infrared source, a light tube, an interference (wavelength) filter, and an infrared detector. The gas is pumped or diffuses into the light tube, and the electronics measures the absorption of the characteristic wavelength of light. NDIR sensors are most often used for measuring carbon dioxide.[1] The best of these have sensitivities of 20-50 PPM.[1] Typical NDIR sensors are still in the (US) $100 to $1000 range. New developments include using Microelectromechanical systems to bring down the costs of this sensor and to create smaller devices (for example for use in air conditioning applications). NDIR CO2 sensors are also used for dissolved CO2 for applications such as beverage carbonation, pharmeceutical fermentation and CO2 sequestration applications. In this care they are mated to an ATR (attenuated total reflection) optic and measure the gas insitu.

[edit] Chemical CO2 SensorsChemical CO2 gas sensors with sensitive layers based on polymer- or heteropolysiloxane have the principal advantage of a very low energy consumption and can be reduced in size to fit into microelectronic-based systems. On the downside, short- and long term drift effects as well as a rather low overall lifetime are major obstacles when compared with the NDIR measurement principle[2].

[edit] Applications

For air conditioning applications these kind of sensors can be used to monitor the quality of air and the tailored need of fresh air, respectively. In applications where direct temperature measurement is not applicable NDIR sensors can be used. The sensors absorb ambient infrared radiation (IR) given off by a heated surface.

Carbon monoxide detectorFrom Wikipedia, the free encyclopedia Jump to: navigation, search The template below (Globalize/North America) is being considered for deletion. See templates for discussion to help reach a consensus.

The examples and perspective in this article deal primarily with North America and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page.

Carbon Monoxide detector connected to a North American power outlet

A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide (CO) gas in order to prevent carbon monoxide poisoning. CO is a colorless and odorless compound produced by incomplete combustion. It is often referred to as the "silent killer" because it is virtually undetectable without using detection technology.[1] Elevated levels of CO can be dangerous to humans depending on the amount present and length of exposure. Smaller concentrations can be harmful over longer periods of time while increasing concentrations require diminishing exposure times to be harmful.[2] CO detectors are designed to measure CO levels over time and sound an alarm before dangerous levels of CO accumulate in an environment, giving people adequate warning to safely ventilate the area or evacuate. Some system-connected detectors also alert a monitoring service that can dispatch emergency services if necessary. While CO detectors do not serve as smoke detectors and vice versa, dual smoke/CO detectors are also sold. Smoke detectors detect the smoke generated by flaming or smoldering fires, whereas CO detectors go into alarm and warn people about dangerous CO buildup caused, for example, by a malfunctioning fuel-burning device. In the home, some common sources of CO include open flames, space heaters, water heaters, blocked chimneys or running a car inside a garage.[3]

Contents[hide]

1 Installation 2 Sensors o 2.1 Opto-Chemical o 2.2 Biomimetic o 2.3 Electrochemical o 2.4 Semiconductor 3 Digital 4 Wireless 5 Legislation 6 Manufacturers 7 References 8 External links

[edit] InstallationThe devices, which retail for $20-$60USD and are widely available, can either be batteryoperated or AC powered (with or without a battery backup). Battery lifetimes have been increasing as the technology has developed and certain battery powered devices now advertise a battery lifetime of over 6 years. All CO detectors have "test" buttons like smoke detectors. CO detectors can be placed near the ceiling or near the floor because CO is very close to the same density as air[4][5].

Since CO is colorless, tasteless and odorless (unlike smoke from a fire), detection in a home environment is impossible without such a warning device. It is a highly toxic inhalant and attracts to the hemoglobin(in the blood stream) 200x faster than oxygen, producing inadequate amounts of oxygen traveling through the body. In North America, some state, provincial and municipal governments have statutes requiring installation of CO detectors in construction among them, the U.S. states of Alaska, Colorado, Connecticut, Florida, Georgia, Illinois, Maryland, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, Texas, Vermont, Virginia, Wisconsin and West Virginia, as well as New York City and the Canadian province of Ontario.[6] When carbon monoxide detectors were introduced into the market, they had a limited lifespan of 2 years. However technology developments have increased this and many now advertise up to 7 years. [7] Newer models are designed to signal a need to be replaced after that time-span although there are many instances of detectors operating far beyond this point. According to the 2005 edition of the carbon monoxide guidelines, NFPA 720 [8], published by the National Fire Protection Association, sections 5.1.1.1 and 5.1.1.2, all CO detectors shall be centrally located outside of each separate sleeping area in the immediate vicinity of the bedrooms, and each detector shall be located on the wall, ceiling or other location as specified in the installation instructions that accompany the unit. Installation locations vary by manufacturer. Manufacturers recommendations differ to a certain degree based on research conducted with each ones specific detector. Therefore, make sure to read the provided installation manual for each detector before installing. CO detectors are available as stand-alone models or system-connected, monitored devices[9]. System-connected detectors, which can be wired to either a security or fire panel, are monitored by a central station. In case the residence is empty, the residents are sleeping or occupants are already suffering from the effects of CO, the central station can be alerted to the high concentrations of CO gas and can send the proper authorities to investigate. The gas sensors in CO alarms have a limited and indeterminable life span, typically two to five years. The test button on a CO alarm only tests the battery and circuitry not the sensor. CO alarms should be tested with an external source of calibrated test gas, as recommended by the latest version of NFPA 720. Alarms over five years old should be replaced but they should be checked on installation and at least annually during the manufacturers warranty period.

[edit] SensorsEarly designs were basically a white pad which would fade to a brownish or blackish colour if carbon monoxide were present. Such chemical detectors are cheap and widely available, but only give a visual warning of a problem. As carbon monoxide related deaths increased during the 1990s, audible alarms became standard. The alarm points on carbon monoxide detectors are not a simple alarm level (as in smoke detectors) but are a concentration-time function. At lower concentrations (eg 100 parts per

million) the detector will not sound an alarm for many tens of minutes. At 400 parts per million (PPM), the alarm will sound within a few minutes. This concentration-time function is intended to mimic the uptake of carbon monoxide in the body while also preventing false alarms due to relatively common sources of carbon monoxide such as cigarette smoke. There are four types of sensors available and they vary in cost, accuracy and speed of response. [10] The latter three types include sensor elements that typically last up to 10 years. At least one CO detector is available which includes a battery and sensor in a replaceable module. Most CO detectors do not have replaceable sensors.

[edit] Opto-ChemicalThe detector consists of a pad of a coloured chemical which changes colour upon reaction with carbon monoxide. They only provide a qualitative warning of the gas however. The main advantage of these detectors is that they are the lowest cost but are also offer the lowest level of protection.

[edit] BiomimeticA biomimetic (chem-optical or gel cell) sensor works with a form of synthetic hemoglobin which darkens in the presence of CO, and lightens without it. This can either be seen directly or connected to a light sensor and alarm. Battery lifespan usually lasts 2-3 years. Device lasts on the average of about 10 years. These products were the first to enter the mass market but have now largely fallen out of favour.

[edit] ElectrochemicalThis is a type of fuel cell that instead of being designed to produce power, is designed to produce a current that is precisely related to the amount of the target gas (in this case carbon monoxide) in the atmosphere. Measurement of the current gives a measure of the concentration of carbon monoxide in the atmosphere. Essentially the electrochemical cell consists of a container, 2 electrodes, connection wires and an electrolyte - typically sulfuric acid. Carbon monoxide is oxidized at one electrode to carbon dioxide while oxygen is consumed at the other electrode. For carbon monoxide detection, the electrochemical cell has advantages over other technologies in that it has a highly accurate and linear output to carbon monoxide concentration, requires minimal power as it is operated at room temperature, and has a long lifetime (typically commercial available cells now have lifetimes of 5 years or greater). Until recently, the cost of these cells and concerns about their long term reliability had limited uptake of this technology in the marketplace, although these concerns are now largely overcome. This technology is now the dominant technology in USA and Europe.

[edit] Semiconductor

Thin wires of the semiconductor tin dioxide on an insulating ceramic base provide a sensor monitored by an integrated circuit. This sensing element needs to be heated to approximately 400 deg C in order to operate. Oxygen increases resistance of the tin dioxide, but carbon monoxide reduces resistance therefore by measurement of the resistance of the sensing element means a monitor can be made to trigger an alarm. The power demands of this sensor means that these devices can only be mains powered although a pulsed sensor is now available that has a limited lifetime (months) as a battery powered detector. Device usually lasts on the average of 5-10 years. This technology has traditionally found high utility in Japan and the far east with some market penetration in USA. However the superior performance of electrochemical cell technology is beginning to displace this technology

[edit] DigitalAlthough all home detectors use an audible alarm signal as the primary indicator, some versions also offer a digital readout of the CO concentration, in parts per million. Typically, they can display both the current reading and a peak reading from memory of the highest level measured over a period of time. These advanced models cost somewhat more but are otherwise similar to the basic models. The digital models offer the advantage of being able to observe levels that are below the alarm threshold, learn about levels that may have occurred during an absence, and assess the degree of hazard if the alarm sounds. They may also aid emergency responders in evaluating the level of past or ongoing exposure or danger.

[edit] WirelessWireless home safety solutions are available that link carbon monoxide detectors to vibrating pillow pads, strobes or a remote warning handset. This allows those with impediments such as hard of hearing, partially sighted, heavy sleepers or the infirm the precious minutes to wake up and get out in the event of carbon monoxide in their property.

[edit] LegislationHouse builders in Colorado will be required to install carbon monoxide detectors in new homes in a bill signed into law in March 2009 by the state legislature. House Bill 1091 requires installation of the detectors in new and resold homes near bedrooms as well as rented apartments and homes. It takes effect from July 1, 2009. The legislation was introduced after the death of Denver investment banker Parker Lofgren and his family. Lofgren, 39; his wife Caroline, 42; and their children, Owen, 10, and Sophie, 8, were found dead in a multimillion-dollar home near Aspen, Colorado on Nov. 27, 2008, victims of carbon-monoxide poisoning. In New York State, Amanda's Law, (A6093A/C.367) requires one- and two-family residences which have fuel burning appliances to have at least one carbon monoxide alarm installed on the

lowest story having a sleeping area, effective February 22, 2010. Although homes built before Jan. 1, 2008 will be allowed to have battery-powered alarms, homes built after that date will need to have hard-wired alarms. In addition, New York State contractors will have to install a carbon monoxide detector when replacing a fuel burning water heater or furnace if the home is without an alarm. The law is named for Amanda Hansen, a teenager who died from carbon monoxide poisoning from a defective boiler while at a sleepover at a friend's house.[11]

[edit] Manufacturers

System Sensor DuPont First Alert Kidde KWJ Engineering, Inc. Sprue Aegis Duomo (UK) Ltd. Ei Electronics (Ireland) www.eielectronics.com Gas Safe Europe Ltd (www.detectagas.com)

Catalytic bead sensorFrom Wikipedia, the free encyclopedia Jump to: navigation, search

A catalytic bead sensor is a type of sensor that is used for gas detection.

Contents[hide]

1 Principle 2 Issues 3 See also 4 References

[edit] Principle

The catalytic bead sensor MSA 94150

The catalytic bead sensor consist of two coils of fine platinum wire each embedded in a bead of alumina, connected electrically in a Wheatstone bridge circuit. One of the pellistors is impregnated with a special catalyst which promotes oxidation whilst the other is treated to inhibit oxidation. Current is passed through the coils so that they reach a temperature at which oxidation of a gas readily occurs at the catalysed bead (500-550C). Passing combustible gas raises the temperature further which increases the resistance of the platinum coil in the catalysed bead, leading to an imbalance of the bridge. This output change is linear, for most gases, up to and beyond 100% LEL, response time is a few seconds to detect alarm levels (around 20% LEL)[1], at least 12% oxygen by volume is needed for the oxidation.

[edit] Issues

Catalyst poisoning - because of the direct contact of the gas with the catalytic surface it may be deactived in some circumstances. Sensor drift - Decreased sensitivity may occur depending on operating and ambient conditions. Modes of failure - which include poisoning and sinter blockage, they become apparent during routine maintenance checking.

Chemical field-effect transistorFrom Wikipedia, the free encyclopedia Jump to: navigation, search This article does not cite any references or sources.Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (December 2009)

ChemFET, or chemical field-effect transistor, is a type of a field-effect transistor acting as a chemical sensor. It is a structural analog of a MOSFET transistor, where the charge on the gate

electrode is applied by a chemical process. It may be used to detect atoms, molecules, and ions in liquids and gases. ISFET, an ion-sensitive field-effect transistor, is the best known subtype of ChemFET devices. It is used to detect ions in electrolytes. ENFET is a CHEMFET specialized for detection of specific enzymes.

Electrochemical gas sensorFrom Wikipedia, the free encyclopedia Jump to: navigation, search This article needs additional citations for verification.Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (June 2008)

Electrochemical gas sensors are gas detectors that measure the concentration of a target gas by oxidizing or reducing the target gas at an electrode and measuring the resulting current.

Contents[hide]

1 Construction 2 Theory of operation 3 Diffusion controlled response 4 Cross sensitivity 5 See also 6 References

[edit] ConstructionThe sensors contain two or three electrodes, occasionally four, in contact with an electrolyte. The electrodes are typically fabricated by fixing a high surface area precious metal on to the porous hydrophobic membrane. The working electrode contacts both the electrolyte and the ambient air to be monitored usually via a porous membrane. The electrolyte most commonly used is a mineral acid, but organic electrolytes are also used for some sensors. The electrodes and housing are usually in a plastic housing which contains a gas entry hole for the gas and electrical contacts.

[edit] Theory of operationThe gas diffuses into the sensor, through the back of the porous membrane to the working electrode where it is oxidized or reduced. This electrochemical reaction results in an electric current that passes through the external circuit. In addition to measuring, amplifying and performing other signal processing functions, the external circuit maintains the voltage across the sensor between the working and counter electrodes for a two electrode sensor or between the working and reference electrodes for a three electrode cell. At the counter electrode an equal and opposite reaction occurs, such that if the working electrode is an oxidation, then the counter electrode is a reduction.HHGGHY

[edit] Diffusion controlled responseThe magnitude of the current is controlled by how much of the target gas is oxidized at the working electrode. Sensors are usually designed so that the gas supply is limited by diffusion and thus the output from the sensor is linearly proportional to the gas concentration. This linear output is one of the advantages of electrochemical sensors over other sensor technologies, (e.g. infrared), whose output must be linearized before they can be used. A linear output allows for more precise measurement of low concentrations and much simpler calibration (only baseline and one point are needed). Diffusion control offers another advantage. Changing the diffusion barrier allows the sensor manufacturer to tailor the sensor to a particular target gas concentration range. In addition, since the diffusion barrier is primarily mechanical, the calibration of electrochemical sensors tends to be more stable over time and so electrochemical sensor based instruments require much less maintenance than some other detection technologies. In principle, the sensitivity can be calculated based on the diffusion properties of the gas path into the sensor, though experimental errors in the measurement of the diffusion properties make the calculation less accurate than calibrating with test gas.[1]

[edit] Cross sensitivityFor some gases such as ethylene oxide, cross sensitivity can be a problem because ethylene oxide requires a very active working electrode catalyst and high operating potential for its oxidation. Therefore gases which are more easily oxidized such as alcohols and carbon monoxide will also give a response. Cross sensitivity problems can be eliminated though through the use of a chemical filter, for example filters that allows the target gas to pass through unimpeded, but which reacts with and removes common interferences. While electrochemical sensors offer many advantages, they are not suitable for every gas. Since the detection mechanism involves the oxidation or reduction of the gas, electrochemical sensors are usually only suitable for gases which are electrochemically active, though it is possible to detect electrochemically inert gases indirectly if the gas interacts with another species in the sensor that then produces a response.[2] Sensors for carbon dioxide are an example of this approach and they have been commercially available for several years.

Electronic noseFrom Wikipedia, the free encyclopedia Jump to: navigation, search

An electronic nose is a device intended to detect odors or flavors. Over the last decade, electronic sensing or e-sensing technologies have undergone important developments from a technical and commercial point of view. The expression electronic sensing refers to the capability of reproducing human senses using sensor arrays and pattern recognition systems. Since 1982[1], research has been conducted to develop technologies, commonly referred to as electronic noses, that could detect and recognize odors and flavors. The stages of the recognition process are similar to human olfaction and are performed for identification, comparison, quantification and other applications. However, hedonic evaluation is a specificity of the human nose given that it is related to subjective opinions. These devices have undergone much development and are now used to fulfill industrial needs.

Contents[hide]

1 Other techniques to analyze odors 2 Electronic Nose working principle 3 How to perform an analysis 4 Range of applications 5 See also 6 References 7 External links

[edit] Other techniques to analyze odorsIn all industries, odor assessment is usually performed by human sensory analysis, Chemosensors or by gas chromatography (GC, GC/MS). The latter technique gives information about volatile organic compounds but the correlation between analytical results and actual odor perception is not direct due to potential interactions between several odorous components.

[edit] Electronic Nose working principleThe electronic nose was developed in order to mimic human olfaction that functions as a nonseparative mechanism: i.e. an odor / flavor is perceived as a global fingerprint.

Electronic Noses include three major parts: a sample delivery system, a detection system, a computing system. The sample delivery system enables the generation of the headspace (volatile compounds) of a sample, which is the fraction analyzed. The system then injects this headspace into the detection system of the electronic nose. The sample delivery system is essential to guarantee constant operating conditions. The detection system, which consists of a sensor set, is the reactive part of the instrument. When in contact with volatile compounds, the sensors react, which means they experience a change of electrical properties. Each sensor is sensitive to all volatile molecules but each in their specific way. Most electronic noses use sensor arrays that react to volatile compounds on contact: the adsorption of volatile compounds on the sensor surface causes a physical change of the sensor. A specific response is recorded by the electronic interface transforming the signal into a digital value. Recorded data are then computed based on statistical models.[2] The more commonly used sensors include metal oxide semiconductors (MOS), conducting polymers (CP), quartz crystal microbalance, surface acoustic wave (SAW), and field effect transistors (MOSFET). In recent years, other types of electronic noses have been developed that utilize mass spectrometry or ultra fast gas chromatography as a detection system.[2] The computing system works to combine the responses of all of the sensors, which represents the input for the data treatment. This part of the instrument performs global fingerprint analysis and provides results and representations that can be easily interpreted. Moreover, the electronic nose results can be correlated to those obtained from other techniques (sensory panel, GC, GC/MS).

[edit] How to perform an analysisAs a first step, an electronic nose need to be trained with qualified samples so as to build a database of reference. Then the instrument can recognize new samples by comparing volatile compounds fingerprint to those contained in its database. Thus they can perform qualitative or quantitative analysis.

[edit] Range of applicationsElectronic nose instruments are used by Research & Development laboratories, Quality Control laboratories and process & production departments for various purposes: in R&D laboratories for:

Formulation or reformulation of products Benchmarking with competitive products

Shelf life and stability studies Selection of raw materials Packaging interaction effects Simplification of consumer preference test

in Quality Control laboratories for at line quality control such as:

Conformity of raw materials, intermediate and final products Batch to batch consistency Detection of contamination, spoilage, adulteration Origin or vendor selection Monitoring of storage conditions.

In process and production departments for:

Managing raw material variability Comparison with a reference product Measurement and comparison of the effects of manufacturing process on products Following-up cleaning in place process efficiency Scale-up monitoring Cleaning in place monitoring.

Various application notes describe analysis in areas such as Flavor & Fragrance, Food & Beverage, Packaging, Pharmaceutical, Cosmetic & Perfumes, Chemical companies. More recently they can also address public concerns in terms of olfactive nuisance monitoring with networks of on-field devices.[3]

Electrolyteinsulatorsemiconductor sensorFrom Wikipedia, the free encyclopedia Jump to: navigation, search The introduction to this article provides insufficient context for those unfamiliar with the subject. Please help improve the article with a good introductory style. (October 2009)

An Electrolyteinsulatorsemiconductor (EIS) sensor is a sensor that is made of these three components:

an electrolyte with the chemical that should be measured an insulator that allows field-effect interaction, without leak currents between the two other components a semiconductor to register the chemical changes

The EIS sensor can be used in combination with other structures, for example to construct a light-addressable potentiometric sensor (LAPS).

Hydrogen sensorFrom Wikipedia, the free encyclopedia Jump to: navigation, search

A hydrogen sensor is a gas detector that detects the presence of hydrogen. They contain microfabricated point-contact hydrogen sensors and are used to locate leaks. They are considered lowcost, compact, durable, and easy to maintain as compared to conventional gas detecting instruments.[1]

Contents[hide]

1 Key Issues o 1.1 Additional requirements 2 Types of microsensors o 2.1 Optical fibre hydrogen sensors o 2.2 Other type hydrogen sensors o 2.3 Enhancement 3 See also 4 References 5 External links

[edit] Key IssuesThere are five key issues with hydrogen detectors:[2]

Reliability: Functionality should be easily verifiable. Performance: Detection 0.5% hydrogen in air or better Response time < 1 second. Lifetime: At least the time between scheduled maintenance. Cost: Goal is $5 per sensor and $30 per controller.

[edit] Additional requirements

Measurement range coverage of 0.1%10.0% concentration[3] Operation in temperatures of -30C to 80C Accuracy within 5% of full scale

Function in an ambient air gas environment within a 10%98% relative humidity range Resistance to hydrocarbon and other interference. Lifetime greater than 10 years

[edit] Types of microsensorsThere are various types of hydrogen microsensors, which use different mechanisms to detect the gas. Palladium is used in many of these, because it selectively absorbs hydrogen gas and forms the compound palladium hydride.[4] Palladium-based sensors have a strong temperature dependence which makes their response time too large at very low temperatures.[5] Palladium sensors have to be protected against carbon monoxide, sulfur dioxide and hydrogen sulfide.

[edit] Optical fibre hydrogen sensorsSeveral types of optical fibre surface plasmon resonance (SPR) sensor are used for the pointcontact detection of hydrogen:

Fiber Bragg grating coated with a palladium layer - Detects the hydrogen by metal hindrance. Micromirror - With a palladium thin layer at the cleaved end, detecting changes in the backreflected light. Tapered fibre coated with palladium - Hydrogen changes the refractive index of the palladium, and consequently the amount of losses in the evanescent wave.

[edit] Other type hydrogen sensors

MEMS hydrogen sensor - The combination of nanotechnology and microelectromechanical systems (MEMS) technology allows the production of a hydrogen microsensor that functions properly at room temperature. The hydrogen sensor is coated with a film consisting of nanostructured indium oxide (In2O3) and tin oxide (SnO2).[6] Thin film sensor - A palladium thin film sensor is based on an opposing property that depends on the nanoscale structures within the thin film. In the thin film, nanosized palladium particles swell when the hydride is formed, and in the process of expanding, some of them form new electrical connections with their neighbors. The resistance decreases because of the increased number of conducting pathways.[2][7] Thick film sensor - Thick film hydrogen sensors rely on the fact that palladium hydride's electrical resistance is greater than the metal's resistance. The absorption of hydrogen causes a measurable increase in electrical resistance. Chemochromic hydrogen sensor - Reversible and irreversible chemochromic hydrogen sensors, a smart pigment paint that visually identifies hydrogen leaks by a change in color. The sensor is also available as tape. [8] [9] Diode based Schottky sensor - A Schottky diode-based hydrogen gas sensor employs a palladium-alloy gate. Hydrogen can be selectively absorbed in the gate, lowering the Schottky energy barrier.[10] A Pd/InGaP metal-

semiconductor (MS) Schottky diode can detect a concentration of 15 parts per million (ppm) H2 in air.[11] Silicon carbide semiconductor or silicon substrates are used. Metallic La-Mg2-Ni which is electrical conductive, absorbs hydrogen near ambient conditions, forming the nonmetallic hydride LaMg2NiH7 an insulator[12].

Sensors are typically calibrated at the manufacturing factory and are valid for the service life of the unit.

[edit] EnhancementSiloxane enhances the sensitivity and reaction time of hydrogen sensors.[4] Detection of hydrogen levels as low as 25 ppm can be achieved; far below hydrogen's lower explosive limit of around 40,000 ppm.

Hydrogen sulfide sensorFrom Wikipedia, the free encyclopedia Jump to: navigation, search

A hydrogen sulfide sensor or H2S sensor is a gas sensor for the measurement of hydrogen sulfide[1].

Contents[hide]

1 2 3 4

Principle Applications Research See also

5 References

[edit] PrincipleThe H2S sensor is a metal oxide semiconductor (MOS) sensor which operates by a reversible change in resistance caused by adsorption and desorption of hydrogen sulfide in a film with hydrogen sulfide sensitive material like tin oxide thick films and gold thin films. Current response time is 25 ppb to 10 ppm < one minute.

[edit] Applications

This type of sensor has been under constant development because of the toxic and corrosive nature of hydrogen sulfide:

The H2S sensor is used to detect hydrogen sulfide in the hydrogen feed stream of fuel cells to prevent catalyst poisoning and to measure the quality of guard beds used to remove sulfur from hydrocarbon fuels[2].

[edit] Research

2004 - a nanocrystalline SnO2Ag on ceramic wafer sensor is reported[3].

Infrared point sensorFrom Wikipedia, the free encyclopedia Jump to: navigation, search

A infrared point sensor is a point gas detector based on the nondispersive infrared sensor technology.

Contents[hide]

1 2 3 4

Principle Micro heaters Range See also

5 External links

[edit] PrincipleDual source and dual receivers are used for self compensation of changes in alignment, light source intensity and component efficiency. The transmitted beams from two infrared sources are superimposed onto an internal beam splitter. 50% of the overlapping sample and reference signal is passed through the gas measuring path and reflected back onto the measuring detector. The presence of combustible gas will reduce the intensity of the sample beam and not the reference beam, with the difference between these two signals being proportional to the concentration of gas present in the measuring path. The other 50% of the overlapped signal passes through the beam splitter and onto the compensation detector. The compensation detector monitors the intensity of the two infrared sources and automatically compensates for any long term drift. Mean time between failures may go up to 15 years.

[edit] Micro heatersMicro heaters can be used to raise the temperature from optical surfaces above ambient to enhance performance and to prevent condensation on the optical surfaces.

[edit] RangeToxic gases are measured in the low parts per million (ppm) range. Flammable gases are measured in the 0 - 100 % lower flammable limit (LFL) or lower explosive limit (LEL) range.

Ion selective electrodeFrom Wikipedia, the free encyclopedia (Redirected from Ion-selective electrode) Jump to: navigation, search

An ion-selective electrode (ISE), also known as a specific ion electrode (SIE), is a transducer (or sensor) that converts the activity of a specific ion dissolved in a solution into an electrical potential, which can be measured by a voltmeter or pH meter. The voltage is theoretically dependent on the logarithm of the ionic activity, according to the Nernst equation. The sensing part of the electrode is usually made as an ion-specific membrane, along with a reference electrode. Ion-selective electrodes are used in biochemical and biophysical research, where measurements of ionic concentration in an aqueous solution are required, usually on a real time basis.

Contents[hide]

1 Types of ion-selective membrane o 1.1 Glass membranes o 1.2 Crystalline membranes o 1.3 Ion-exchange resin membranes 1.3.1 Construction 1.3.2 Applications o 1.4 Enzyme electrodes 2 Interferences 3 See also 4 References 5 External links

[edit] Types of ion-selective membraneThere are four main types of ion-selective membrane used in ion-selective electrodes: glass, solid state, liquid based, and compound electrode.

[edit] Glass membranesGlass membranes are made from an ion-exchange type of glass (silicate or chalcogenide). This type of ISE has good selectivity, but only for several single-charged cations; mainly H+, Na+, and Ag+. Chalcogenide glass also has selectivity for double-charged metal ions, such as Pb2+, and Cd2+. The glass membrane has excellent chemical durability and can work in very aggressive media. A very common example of this type of electrode is the pH glass electrode.

[edit] Crystalline membranesCrystalline membranes are made from mono- or polycrystallites of a single substance. They have good selectivity, because only ions which can introduce themselves into the crystal structure can interfere with the electrode response. Selectivity of crystalline membranes can be for both cation and anion of the membrane-forming substance. An example is the fluoride selective electrode based on LaF3 crystals.

[edit] Ion-exchange resin membranesIon-exchange resins are based on special organic polymer membranes which contain a specific ion-exchange substance (resin). This is the most widespread type of ion-specific electrode. Usage of specific resins allows preparation of selective electrodes for tens of different ions, both singleatom or multi-atom. They are also the most widespread electrodes with anionic selectivity. However, such electrodes have low chemical and physical durability as well as "survival time". An example is the potassium selective electrode, based on valinomycin as an ion-exchange agent. [edit] Construction These electrodes are prepared from glass capillary tubing approximately 2 millimeters in diameter, a large batch at a time. Polyvinyl chloride is dissolved in a solvent and plasticizers (typically phthalates) added, in the standard fashion used when making something out of vinyl. In order to provide the ionic specificity, a specific ion channel or carrier is added to the solution; this allows the ion to pass through the vinyl, which prevents the passage of other ions and water. One end of a piece of capillary tubing about an inch or two long is dipped into this solution and removed to let the vinyl solidify into a plug at that end of the tube. Using a syringe and needle, the tube is filled with salt solution from the other end, and may be stored in a bath of the salt solution for an indeterminate period. For convenience in use, the open end of the tubing is fitted through a tight o-ring into a somewhat larger diameter tubing containing the same salt solution,

with a silver or platinum electrode wire inserted. New electrode tips can thus be changed very quickly by simply removing the older electrode and replacing it with a new one. [edit] Applications In use, the electrode wire is connected to