Matrix is the medium in which the analyte is analyzed.What is Sample?

TYPES OF ANALYSISQualitative analysis is performed to identify what material/analyte present in a sample.Quantitative analysis is an analysis to determine how much of a material is present in a sample.

ANALYTICAL CHEMISTRYANALYTICAL CHEMISTRYAnalytical chemistry is branch of chemistry that deals with the separation, identification, and determination of component (analyte) in a sample.

Analyte is the substance to be identified, detected, or separated in some manner.

A

SAMPLE

AREAS OF ANALYTICAL CHEMISTRYClinical analysis: blood, urine, feces, cellular fluids, etc., for use in diagnosis. Pharmaceutical analysis: establish the physical properties, toxicity, metabolites, quality control, etc.

Environmental analysis: pollutants, soil and water analysis, pesticides. Forensic analysis: analysis related to criminology; DNA finger printing, finger print detection; blood analysis.

Industrial quality control: required by most companies to control product quality.

Bioanalytical chemistry and analysis: detection and/or analysis of biological components (i.e., proteins, DNA, RNA, carbohydrates).

ANALYTICAL CHEMIST/ANALYST?A true analyst has several characteristics:Has knowledge of the methods and instruments used for analysis.Understands the principles of analysis, so that he/she can apply and if necessary modify analytical methods to solve a particular problem.Can develop new methods of analysis.Can evaluate and interpret the result of a quantitative analysis.

An analytical chemist is a skilled and well-trained chemist and also known as

a problem solver.

CLASSIFICATION OF Analytical methods

Gravimetric MethodsMeasure the mass of the analyte (or a compound chemically related to the analyte).

Volumetric MethodsMeasure the volume of a solution containing sufficient reagent to react with the analyte (i.e., titration or gas analysis).

Separation MethodsMeasure the peak areas of the separated components of a sample.

Spectroscopic MethodsMeasuring the interaction between the analyte and electromagnetic radiation (or the production of radiation by an analyte).

Electroanalytical MethodsMeasure an electrical property (i.e., potential, current, amperes) which is chemically related to the amount of analyte.

STEPS IN A QUANTITATIVE ANALYSIS

Define the problem

Select a method

Sample Preparation

Eliminate interferences

Perform the measurement

Calculate the results and report writing

sampling

Definition of the ProblemLearn as much as possible about the overall problem that is being faced.The analyst must know;

What is the problem? What needs to be found? (Qualitative and/or quantitative?)Who will use the information – to provide evidence for possible future litigation, to help improve company profit or to satisfy a customer.When will the result be needed?How many samples are to be analyzed?

What type of sample is to be analyzed (physical state of the sample)?

After the problem is defined this will dictate to:How accurate and precise does it have to be (how sensitive the method must be?)?What is the budget?How the sample is to be obtained?What are the physical or chemical properties of the laboratory sample?Is it required any preliminary treatment (what separation may be required to eliminate interferences?)

METHOD SELECTION.

Factors to consider include:•Accuracy •Detection limit •Time•Cost/number of analyses•Complexity of sample - selectivity.•Equipment•Technical expertise •Speed•Does it need to be automated?•Are methods available in the chemical literature?•Analyst, Analytica Chimica Acta, Journal of Analytical Chemistry, Journal of Chromatography.•Standard methods available?•Legality- how well an analytical method will stand up in court.

•CHOOSEN METHOD MUST BE VALID/CERTIFIED•IF NOT VALID?

VALIDATION OF ANALYTICAL METHOD

•The Analysis of Standard Samples(A sample whose analyte concentration is known)The standard reference samples (SRM) can be obtained from The National Institute Of Standard and Technology (NIST).The analyte concentration in the SRM has been certified by the institute. Compare the data obtained from the method with the certified value.

•Analysis by Other MethodsThe result of the analytical method can be evaluated by comparison with data obtained from a different method.

•Standard Addition to the Sample The known amount of the analyte is added to the sample and then analyzed by the proposed method. The effectiveness of the method can be established by evaluating the recovery of the added quantity.The standard addition method will reveal errors arising from the way the sample was treated or from the presence of the other compounds in the matrix.

SAMPLINGSampling is the process to get a representative and homogeneous

sample.Representative means that content of analytical sample reflects content

of bulk sample.Homogeneous means that the analytical sample has the same content

throughout.

Deciding how to obtain a sample for analysis depend on:i. The size of the bulk to be sampled.ii. The physical state of the fraction to be analyzed.(solid, liquid, gas)iii. The chemistry of the material to be assayed.(Nothing can be done that would destroy or alter the identity or quantity

of the analyte)

Steps involved in sampling bulk material:• Identify the population from which the sample is to be obtained.• Collect a gross sample that is truly representative of the population

being sampled.• Reduce the gross sample to a laboratory sample that is suitable for

analysis.

SAMPLING SOLIDS•Inhomogeneity of the material, make sampling of solids more difficult.

•The easiest way to sample a material is grab sample – the sample taken at random and assumed to be representative.

•For reliable results, it is best to take 1/50 to 1/100 of the total bulk. The larger the particle size, the larger the gross sample should be.

Examples:•Stockpile of cereals: take increment from surface and interior.•Compact solids (metals and alloys): obtained by random drilling or by sawing across the metal at random intervals and collecting the `sawdust’ as the sample.

•Obtaining a random sample from a bulky material (ore, grain, coal) can be achieved while the material in motion (conveyor belt). Periodically transfer portion into a sample container.

•The gross sample must be reduced in size to obtain a laboratory sample.

•The sample is crushed and mixed to form a conical pile. This pile is flattened and cut into equal quarters, and two opposite quarters are chosen at random. The procedure is called coning and quartering. This process is continued until the gross sample is small enough to be transported to the laboratory.

SAMPLING LIQUIDS•Liquid samples are homogeneous and are much easier to sample.•The gross sample can be relatively small.•If liquid samples are not homogeneous, and have only small quantity, they can be shaken and sampled immediately.•Sampling techniques will depend on the types of liquid.Example:Large volume of liquids (impossible to mix)Sampled after transfer (during discharge) or if in a pipe, sampled after passing through a pump or at different points in pipe system.Large stationary liquids (lakes, rivers)Samples may be obtained at different depths using a sample thief (a bottle that can be opened and filled at any desired location in the solution). The separate aliquots of liquids can be analyzed individually or can be combined into one gross sample (composite sample) and replicate analyses performed.

Biological fluidsThe timing of sampling is very important. For example, the composition of blood varies before and after meal. The sample is collected after the patient has fasted for a number of hours.

SAMPLING GASES•Tend to be homogeneous.

•Large volume of samples is required because of their low density.•Examples:

•Air analysis: Use a `Hi-Vol’ sampler that is containing filters to collect particulates.

•Liquid displacement method: The sample must has little solubility in the liquid and does not react with the liquid

•Breath sample: The subject could blow into evacuated bag.

SAMPLE STORAGE AND PRESERVATIONAn important aspect of the sampling process.

Objective:

To make sample contains as same as during the sampling process.

MECHANISM OF PREVENTION:•Decomposition of biological samples through the action of bacteria. Refrigerated after collection until the time of analysis.•Precipitation of metals from water samples. Acidified (10% HNO3) immediately upon collection.•Loss of water from hygroscopic material.•Loss of volatile analytes from water samples.

•Use an appropriate container to store the sample e.g. glass is not suitable for inorganic trace analyses, low molecular weight polyethylene is not suitable for hydrocarbon samples.

PREPARING A LABORATORY SAMPLE•Converting the sample to a useful form:•Solids are usually ground to a suitable particulate size to get a homogeneous sample.•Dry the samples to get rid of absorption water. (Drying at 110 to 120C for 1 hour and cooled in dessicator before weighing).DEFINING REPLICATE SAMPLES•Replicate samples are always performed unless the quantity of the analyte, expense or other factors prohibit. •Replicate samples are portion of a material of approximately the same size that is carried through an analytical procedure at the same time and the same way.

PREPARING SOLUTIONS OF THE SAMPLE•Most analyses are performed on solutions. •A solvent is chosen that dissolves the whole sample without decomposing the analyte.•Several sources of error are encountered in the sample dissolution step:

•Incomplete dissolution of the analyte.•Losses of analyte by the volatilization.•Introduction of analyte as a solvent contamination.•Contamination from the reaction of the solvent with vessel walls.

SAMPLE PREPARATION AND DISSOLUTION

Decomposition and Dissolution of Inorganic Solids

•Simple DissolutionDissolution by water.

Acid TreatmentHydrochloric acid, nitric acid, perchloric acid.

•Fusion TechniquesThe sample is mixed with flux (1:10), heated (300 – 1000C) in the crucible until molten. Then dissolve in dilute acid or water.Base flux (carbonates, hydroxides of alkaline metal)Acid flux (pirosulfates, boric oxide, fluoride acids)

Decomposition of Organic Matrices for Elemental Analysis

Dry Ashing•The method consists of preparing an ash by using heat and water/nitric acid to decompose the organic matter, and dissolving the inorganic residue in an appropriate volume of dilute hydrochloric acid. •The sample is place in crucible and heat in furnace up to 450C.

Wet Digestion•HCl: Carbonates, phosphates, oxides•H2SO4: Organic material at 300C•HNO3: Any metals not dissolve by HCl•HClO4: Steel•HF: Silica•Aqua Regia (HCl:HNO3, 3:1): Not stable•HNO3:HCl:HF (5:15:3): Alloys

MICROWAVE DECOMPOSITION

•The best method for converting the liquid or solid sample into solution.

•The advantages of microwave digestion include:

•Sample contained within the digestion vessel.

•Highly efficient.

•Mostly any sample can be digested.

•Volatile elements are retained in the reaction vessel.

•Easy to automate: a computer controls the pressure and the temperature.

ELIMINATING INTERFERENCESInterferences are substances that prevent direct measurement of the analyte and must be removed.

CALIBRATION AND MEASUREMENT•The physical or chemical property proportional to the analyte concentration is measured.

•Suitable standards must be measured to determine the relationship between analyte quantity and the physical/chemical property being measured (i.e., calibration).

CALCULATING RESULTSThis requires using the raw data, stoichiometry of the reaction(s) and instrumental factors to calculate the analyte concentration.Evaluating the results and estimating their reliability. This requires appropriate use of statistics.

REPORTReport results with limitation/accuracy information.A professional chemist/charted chemist should verify the report.