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INSTRUMENTAL ANALYSIS

VT 2013
(C) HKD 2013

CLASSICAL ANALYTICAL METHODS
‰ Wet-chemical methods
‰ Separation of component of interest (analyte) from the sample by
precipitation, extraction, or distillation.
‰ Followed by gravimetric or titrimetric measurement for quantitative
analysis.

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INSTRUMENTAL ANALYSIS

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INSTRUMENTAL ANALYSIS
‰ Instrument converts information stored in the physical or chemical
characteristics of the analyte into useful information.
‰ Require a source of energy to stimulate measurable response from
analyte.
‰ Data domains
9 Methods of encoding information electrically.
9 Nonelectrical domains.
9 Electrical domains.
9 Analog, Time, Digital.

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INSTRUMENTAL ANALYSIS
‰ Detector
9 Device that indicates a change in one variable in its environment (eg.,
pressure, temp, particles).
9 Can be mechanical, electrical, or chemical.
‰ Sensor
9 Analytical device capable of monitoring specific chemical species
continuously and reversibly.
‰ Transducer
9 Devices that convert information in nonelectrical domains to electrical
domains and the converse.

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METHOD SELECTION
‰ 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.

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ACCURACY vs PRECISION
‰ Accuracy
9 Describes the correctness of an experimental result.

9 Absolute error.
9 Relative error.
‰ Precision
9 Describes the reproducibility of results.
9 Standard deviation.
9 Variance.
9 Coefficient of variation.
9 Relative standard deviation.

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ACCURACY vs PRECISION

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SENSITIVITY
‰ Sensitivity of an instrument or method is its ability to discriminate between
small differences in analyte concentration.
‰ S = mc + Sbl
S = measured signal; c= analyte concentration;
Sbl = blank signal; m = sensitivity (Slope of line).
‰ Analytical sensitivity (J)
J = m/ss
m = slope of the calibration curve
ss = standard deviation of the measurement
‰ 2 factors limit sensitivity
9 Slope of calibration curve.
9 Precision of measuring device.
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CALIBRATION CURVE

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CALIBRATION CURVE
‰ Least-square regression line
Y = b0 + b1X

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CALIBRATION CURVE
External Standard Method

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CALIBRATION CURVE
Internal Standard Method

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CALIBRATION CURVE
Standard Addition Method

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DETECTION LIMIT

‰ Detection limit: the minimum concentration or mass of analyte that can be
detected at a known confidence level. LOD is determined by S/N, where, S/N =
Signal-to-noise ratio = (magnitude of the signal)/(magnitude of the noise).
‰ Cm = (Sm – Sbl)/m, where, Cm = minimum concentration i.e., LOD, Sm =
minimum distinguishable analytical signal (i.e., S/N = 2 or S/N = 3), Sbl = mean
blank signal

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LINEARITY
‰ Linear range: extends from the lowest concentration at which quantitative
measurements can be made (LOQ), to the concentration at which the
calibration curve departs from linearity (LOL).

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INSTRUMENTAL METHODS
‰ Chromatographic methods
9 Gas chromatography.
9 Liquid chromatography.
‰ Spectrophotometric methods
9 Absorption: Atomic absorption, Molecular absorption (UV-Vis, IR).
9 Inductively coupled plasma.
‰ Spectroscopic methods
9 Mass-spectrometry.
9 Nuclear Magnetic Resonance spectrometry.

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APPLICATIONS
‰ Bioanalytical: biological molecules and/or biological matrices (e.g., proteins,
amino acids, blood, urine)
‰ Environmental: pesticides, pollution, air, water, soil
‰ Material science: polymers, characterization of new materials
‰ Forensic science (application of science to the law): body fluids, DNA, gun
shot residue, hair, fibers, elemental analysis, drugs, alcohols, poisoning,
fingerprints, etc.

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METHODOLOGY
‰ Plan: Qualitative or quantitative or both; what kind of information have; which
technique is suitable etc.
‰ Sampling: Accuracy depends on proper sampling, characteristic of sample is
very important, required good representative sample (from top, middle and
bottom and mix up and take average sample).
‰ Sample preparation: depends on analytical techniques.
‰ Analytical measurement
‰ Data Analysis: Whether the data make sense or not.

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