lecture 1 introduction to instrumental analysis copyright ©the mcgraw-hill companies, inc....
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Lecture 1 INTRODUCTION TO INSTRUMENTAL ANALYSIS
Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
INTRODUCTION
OUTLINE:
CLASSIFICATION OF ANALYTICAL METHODS
TYPES OF INSTRUMENTAL METHODS
INSTRUMENTS FOR ANALYSIS
SELECTING AN ANALYTICAL METHOD
CALIBRATION OF AN INSTRUMENTAL METHODS
Problem set:
1-4, 1-9, 1-10, 1-11
CLASSIFICATION OF ANALYTICAL METHODS
Classical vs Instrumental
Qualitative instrumental analysis is that measured property that indicates presence of analyte in matrix
Quantitative instrumental analysis is that magnitude of measured property that is proportional to concentration of analyte in matrix
Species of interestAll constituents including analyte.
Often need pretreatment - chemical extraction, distillation,separation, precipitation
INTRODUCTION
CLASSICAL:Qualitative - identification by color, indicators, boiling points,odors
Quantitative - mass or volume (e.g. gravimetric, volumetric)
INSTRUMENTAL:Qualitative - chromatography, electrophoresis and identification by measuring
physical property (e.g. spectroscopy, electrode potential)
Quantitative - measuring property and determining relationship to concentration (e.g. spectrophotometry, mass spectrometry). Often, same instrumental method used for qualitative and quantitative analysis.
TYPES OF INSTRUMENTAL METHODS
PROPERTY EXAMPLE METHOD
Radiation Emission Emission spectroscopy - fluorescence,phosphorescence, luminescence
Radiation Absorption Absorption spectroscopy -spectrophotometry, photometry, nuclearmagnetic resonance, electron spinresonance
Radiation Scaterring Turbidity, Raman
Radiation Refraction Refractometry, interferometry
Radiation Diffraction X-ray, electron
Radiation Rotation Polarimetry, circular dichroism
TYPES OF INSTRUMENTAL METHODS
PROPERTY EXAMPLE METHOD
Electrical Potential Potentiometry
Electrical Charge Coulometry
Electric Current Voltammetry - amperometry, polarography
Electrical Resistance Conductometry
Mass Gravimetry
Mass-to-charge Ratio Mass spectrometry
Rate of Reaction Stopped flow, flow injection analysis
Thermal Characteristics Thermal gravimetry, calorimetry
Radioactivity Activation, isotope dilution
Often combined with chromatographic or electrophoretic methods
INSTRUMENTS FOR ANALYSIS
Example: spectrophotometryInstrument: spectrophotometerStimulus: monochromatic light energyAnalytical response: light absorptionTransducer: photocellData: electrical currentData processor: current meterReadout: meter scale
Block diagram for the overall process of instrumental measurement.
INSTRUMENTS FOR ANALYSIS
DATA DOMAINS: way of encoding analytical response in electrical or non-electrical signals.
Interdomain conversions transform information from one domain to another.
Detector : device that indicates change in environmentTransducer : device that converts non-electrical to electrical dataSensor : device that converts chemical to electrical data
INSTRUMENTS FOR ANALYSIS: DOMAINS
NON-ELECTRICAL DOMAINS ELECTRICAL DOMAINS
Physical (light intensity, color) Current (Analog)
Chemical (pH) Voltage (Analog)
Scale Position (length) Charge (Analog)
Number (objects) Frequecy (Time)
Pulse width (Time)
Phase (Time)
Count (Digital)
Serial (Digital)
Parallel (Digital)
Time: vary with time (frequency, phase, pulse width)Analog: continuously variable magnitude (current, voltage, charge)Digital: discrete values (count, serial, parallel, number*)
Advantages: (1) easy to store (2) not susceptible to
noise
DIGITAL BINARY DATA
What accuracy is required?
How much sample is available?
What is the concentration range of the analyte?
What components of the sample will cause interference?
What are the physical and chemical properties of the sample matrix?
How many samples are to be analyzed?
DEFINING THE PROBLEM
Performance Characteristics: Figures of Merit
How to choose an analytical method? How good is measurement?How reproducible? - Precision
How close to true value? - Accuracy/BiasHow small a difference can be measured? - Sensitivity
What range of amounts? - Dynamic RangeHow much interference? - Selectivity
SELECTING AN ANALYTICAL METHOD
INDETERMINATE OR RANDOM ERRORS
FIGURES OF MERIT: PRECISION
FIGURES OF MERIT: ACCURACY
DETERMINATE ERRORS (operator, method, instrumental)
FIGURES OF MERIT: SENSITIVITY
(larger slope of calibration curve m, more sensitive measurement)
Signal must be bigger than random noise of blank
FIGURES OF MERIT: DETECTION LIMIT
At detection limit we can say confidently analyte is present but cannot perform reliable quantitation
Level of quantitation (LOQ): k=10Limit of linearity (LOL): when signal is no longer proportional to concentration
FIGURES OF MERIT: DYNAMIC RANGE
No analytical method is completely free from interference by concomitants. Best method is more sensitive to analyte than interfering species (interferent).
k's vary between 0 (no selectivity) and large number (very selective).
FIGURES OF MERIT: SELECTIVITY
Basis of quantitative analysis is magnitude of measured property is proportional to concentration of analyte
CALIBRATION METHODS
CALIBRATION CURVES (WORKING or ANALYTICAL)
SAMPLE PROBLEM:
SAMPLE PROBLEM
SAMPLE PROBLEM
Calibration Curves:several standards containing exactly known
concentrations of the analytes are introduced into the instrument and the response is recorded.
CALIBRATION OF INSTRUMENTAL METHODS
STANDARD ADDITION METHOD
An internal standard is added in constant amount to samples, blanks, and calibration.
The analyte to internal standard signal as a function of the analyte concentration is determined.
The ratio for the samples is then used to obtain their analyte concentrations from a working curve.
INTERNAL STANDARD METHOD
TRANSFORMATION OF ALKENES AND ALKYNES
TRANSFORMATION OF ALKENES AND ALKYNES
TRANSFORMATION OF ALKENES AND ALKYNES
TRANSFORMATION OF ALKENES AND ALKYNES
TRANSFORMATION OF ALKENES AND ALKYNES