[1] INSTRUMENTAL METHODS OF ANALYSIS

CLASSICAL / WET-CHEMICAL METHOD

• measurement depends on the chemical properties of the sample

• reagent is made to react completely with the analyte

• relationship between the measured signal and analyte concentration is determined by chemical stoichiometry

CLASSICAL / WET-CHEMICAL METHOD

• measurement depends on the

chemical properties of the sample

CLASSICAL / WET-CHEMICAL METHOD

• reagent is made to

react completely with the analyte

CLASSICAL / WET-CHEMICAL METHOD

• relationship between the measured signal and analyte concentration is determined by

chemical stoichiometry

CLASSICAL / WET-CHEMICAL METHOD

separation

• precipitation

• extraction

• distillation

CLASSICAL / WET-CHEMICAL METHOD

qualitative analyses

• colors

• boiling or melting points

• solubility

• odors

• Optical activity

• Refractive index

CLASSICAL / WET-CHEMICAL METHOD

quantitative analyses

• gravimetric

• volumetric

CLASSICAL / WET-CHEMICAL METHOD

Charaacteristics

• more suitable for analysis of major constituents

• used to certify analytical standards

• generally cheaper

• more accurate and precise

• more robust and less susceptible to environmental fluctuations

CLASSICAL / WET-CHEMICAL METHOD

More suitable for analysis of

major constituents

CLASSICAL / WET-CHEMICAL METHOD

• used to

certify analytical standards

CLASSICAL / WET-CHEMICAL METHOD

• generally:

• cheaper

• more accurate & precise

• more robust and less susceptible to environmental fluctuations

INSTRUMENTAL METHOD

measurement of physical or chemical properties of the analyte

INSTRUMENTAL METHOD

separation

• chromatography (tlc is not included)

• electrophoretic techniques

INSTRUMENTAL METHOD

quantitative analyses

• conductivity electrode potential

• light absorption or emission

• massto-charge ratio

• fluorescence

INSTRUMENTAL METHOD

characteristics

• ability to perform trace analysis

• most are multi-channel techniques

• shorter analysis time

• ammendable to automation

• more samples may be analyzed quickly

• less skill and training required

INSTRUMENTAL METHOD

• ability to __

perform trace analysis

INSTRUMENTAL METHOD

• most are

• multi-channel techniques; shorter analysis time

• more samples may be analyzed quickly

INSTRUMENTAL METHOD

• ammendable to

automation

INSTRUMENTAL METHOD

• Less __

skill and training required

Types of Instrumental Methods

• spectrometric methods

• electrochemical methods

• chromatographic methods

• miscellaneous methods

Spectrometric Methods

• Emission

• Absorption

• Scattering

• Refraction

• Diffraction

• Rotation

Emission

• Emission spectroscopy (X-ray, UV, visible, electron, Auger)

• Fluorescence

• Phosphorescence and Luminescence (Xray, UV and visible)

Emission spectroscopy

(X-ray, UV, visible, electron, Auger)

Phosphorescence and Luminescence

(Xray, UV and visible)

Absorption

• Spectrophotometry and photometry (X-ray, UV, IR)

• Photoacoustic spectroscopy

• Nuclear magnetic resonance and electron spin resonance spectroscopy

Spectrophotometry and photometry

(X-ray, UV, IR)

Scattering

• Turbidimetry

• Nephelometry

• Raman spectroscopy

Refraction

• Refractometry

• Interferometry

Diffraction

• X-ray

• Electron diffraction methods

Rotation

• Polarimetry

• Optical rotary dispersion

• Circular dichroism

Chromatographic Methods

• GC

• HPLC

Electrochemical Methods

• conductometry

• coulometry

• polarography

• potentiometry

conductometry

resistance

coulometry

charge

polarography

current

potentiometry

potential

Miscellaneous Methods

• Mass-to-charge ratio

• Thermal characteristics

• Radioactivity

Mass-to-charge ratio

Mass spectrometry

Thermal characteristics

• Thermal gravimetry and titrimetry

• Differential scanning calorimetry

• Differential thermal analyses

• Thermal conductometric methods

Radioactivity

Activation and isotope dilution methods

ANALYTICAL INSTRUMENTS

converts information about the physical or chemical characteristics of the analyte to information that can be manipulated and interpreted by man

General Components of Instrumental Measurement

• signal generator (energy source, chemical system)

• transducter or detector

• signal processor

• read-out device

Signal generator

• consists of the chemical system interacting with the stimulus from the energy source

• producing an analytical signal reflecting the presence and usually the concentration of the analyte

Transducer or Detector

transforms the analytical signal produced by the signal generator into an electrical signal

Signal processor

modifies and “cleans up” the electrical signal to make it more convenient to interpret

3 things that a signal processor provide

• attenuation

• amplification

• filtering

attenuation

lessen the signal to make it more convenient to interpret

amplification

make the signal stronger to make it easier to interpret

filtering

removal of noise

read-out device

converts the electrical signal to a form usable to the analyst

Calibration

determines the relationship between the analytical response and the analyte concentration.

CALIBRATION OF INSTRUMENTAL METHODS

1.Comparison with standards

2.External standard calibration

3.Standard addition method

4.Internal standard method

Comparison with standards

direct comparison

property of the analyte is compared with standards such that the property being tested matches the standard

Comparison with standards

direct comparison: conc of analyte was then __

equal to the concentration of the standard after dilution

Comparison with standards

titration

• the most accurate of all analytical procedures

• analyte reacts with a standardized reagent in a reaction of known stoichiometry

sem

Comparison with standards

titration: amount of the standardized reagent needed to achieve chemical equivalence can then be __

related to the amount of analyte present

External standard calibration

External standard

• used to calibrate instruments and procedures when there are no interference effects from matrix components in the analyte solution

• prepared separately from the sample

External standard calibration

External standard: series of such __

external standards containing the analyte in known concentrations is prepared

External standard calibration

External standard: response signal __

is obtained (absorbance, peak height, peak area) as a function of known analyte concentration

External standard calibration

External standard: calibration curve

prepared by plotting the data or by fitting them to a suitable mathematical equation, such as the slope-intercept form used in the method of linear least squares

External standard calibration

External standard: response signal is then obtained for the sample and used to __

predict the unknown analyte concentration from the calibration curve or bestfit equation

Standard addition method

useful for analyzing complex samples in which the likelihood of matrix effects is substantial

Standard addition method

spiking

adding one or more increments of a standard solution to sample aliquots containing identical volumes

Internal standard method

internal standard

substance that is added in a constant amount to all samples, blanks, and calibration standards in an analysis

Internal standard method

• calibration __

involves plotting the ratio of the analyte signal to the internal-standard signal as a function of the analyte concentration of the standards

Internal standard method

• this ratio for the sample is then used to

obtain their analyte concentration from a calibration curve

SIGNAL

analytical measurement that carries information about the analyte that is of interest to the scientist

SIGNAL

examples

• absorbance

• peak area

• peak location

• peak height

• retention time

NOISE

analytical measurement made up of extraneous information that is unwanted

NOISE

• it degrades the __

accuracy and precision of an analysis and also places a lower limit on the amount of analyte that can be detected

Chemical Noise

• arise from a __

host of uncontrollable variables that affect the chemistry of the system being analyzed

Factors that affect the sx

• undetected variations in temperature or pressure

• fluctuations in relative humidity

• vibrations that lead to stratification of powdered solids

• changes in light intensity

• laboratory fumes

Instrumental Noise

associated with each component of an instrument

SIGNAL-TO-NOISE (S/N) RATIO

equation that indicates the magnitude of an experimental effect above the effect of experimental error due to chance fluctuations

International Council for Harmonisation (ICH)

an international non-profit organization that aims to develop guidelines via a process of scientific consensus with regulatory and industry experts working together

Out-of-control process

a process in which variations among the observed sampling results cannot be attributed to a constant system of chance causes

Out of specifications (OOS) result

a result that falls outside established acceptance criteria which have been established in official compendia and/or by company documentation

Out of trend (OOT) result

a time-dependent result which falls outside a prediction interval or fails a statistical process control criterion

Standard

the metric, specification, gauge, statement, category or physical product sample against which the outputs of a process are compared and declared acceptable or unacceptable

Specification

a list of tests, references to analytical procedures, and appropriate acceptance criteria that are numerical limits, ranges, or other criteria for the test described

Specification establishes __

the set of criteria to which a material should conform to be considered acceptable for its intended use

System suitability test

• used to __

verify that the test system will perform in accordance with the criteria set forth in the procedure

System suitability test

• the tests are based on __

the concept that the equipment, electronics, analytical operations, and samples analyzed constitute an integral system that can be evaluated as such

Out of specifications (OOS) result

example

Out-of-control process

• example

• one point or more fall outside of the control limits

• seven consecutive points steadily increasing or decreasing

• eight consecutive points on one side of the average

• fourteen consecutive points in an up and down pattern

• 2 out of 3 consecutive points in zone a or beyond

• 4 out of 4 consecutive points in a row in zone B or beyond

• fifteen consecutive points in zone c