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Analytical Chemistry IISomsak Sirichai

Lectures: Tuesday 1.00-3.00 p.m. Friday 8.00-9.00 a.m. C310

303354

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Course Description:Teach fundamental of instrumentation analysis

Spectrochemical analysis

Electrochemical analysis

Chromatographic analysis

Capillary Electrophoresis

UV-VIS, IR, Fluorescence & Phosphorescence,AA, ICP, X-ray, NMR, MS

Potentiometry, Coulometry, Voltammetry

GC, HPLC

CZE

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Gradings

• 2 exams (mid-term, final each worth 40%)• Quizzes (10%)• Paper (10%)

<40% F

Texts:Skoog & Leary, Principles of Instrumental Analysis*Weston & Brown, HPLC and CEKhaledi; High Performance Capillary Electrophoresis

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Introduction

AnalysisQualitative analysis (1)

Quantitative analysis (2)

(1) A type of chemical analysis by which the analyte or analytes in a sample are identified.

(2) A type of chemical analysis by which the amount of each analyte or analytes in a sample is determined.

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analyte(s)

matrix

Matrix-analyte = concomitants

the species to be determinded in the sample

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Classification of Analytical Methods

1. Classical methods

Qualitative – identification by color,indicators, boiling or melting points, odors

Quantitative – mass or volume(e.g. gravimetric, volumetric)

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2. Instrumental methodsQualitative – 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.

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Types of Instrumental Methods

Signal Example MethodRadiation emission Emission spectroscopy (X-ray, UV, visible), fluorescence, phosphorescence, luminescence

Radiation absorption Absorption spectroscopy spectrophotometry, photometry, NMR electron spin resonance

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Signal Example MethodRadiation Scattering Raman spectroscopy Radiation refraction Refractometry

Radiation diffraction X-ray and Electron diffraction method

Radiation rotation Polarimetry

Electrical potential Potentiometry

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Signal Example MethodElectrical charge Coulometry Electrical current Voltammetry – amperometry polarography

Electrical resistance Conductometry

Mass Gravimetry

Mass-to-charge ratio Mass spectrometry

Rate of reaction Flow injection analysis

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Instruments for Analysis

DataEnergystimulus

Analytes

(in matrix)

Analyticalresponse

Example: SpectrophotometryInstrument: spectrophotometerStimulus: monochromatic light energyAnalytical response: photocellData: electrical currentData processor: current meterReadout: meter scale

Encodedinformation

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Encoded information: detector : device that indicates changes in environment transducer : device that converts non-electrical to electrical data

Non-electrical domians Electrical domains

Physical Current(light intensity, colour) Chemical (pH) Voltage

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Selecting an Analytical MethodDefining the ProblemA definition requires answers to the followingquestions:

1. What accuracy and precision are required?2. How much sample is available?3. What is the concentration range of the analyte?4. What components of the sample will cause interference?5. What are the physical and chemical properties of the sample matrix? 6. How many samples are to be analysed?

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Performance Characteristics ofInstruments; Figures of Merit

Precision: Indeterminate or random errors

• Absolute standard deviation (s)• Relative standard deviation (RSD)• Variance (s2)• Coefficient of variation (a percentage) (CV)• Standard deviation of means (sm)

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1

)(1

2

N

xxs

N

ii

xsRSD

%100xxsCV

Nss m

Absolute standard Deviation (s)

Relative standard deviation (RSD)

Coefficient of Variation (CV)

Standard deviation of means (sm)

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Accuracy: determinate errors (operator, method, instrumental)

% Relative error (%Er)

100% xxxx

Et

tir

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Sensitivity:“the ability to detect (qualitative analysis)or determine (quantitative analysis) small amounts of an analyte in a sample”

CxS x = analytical signal

C = the analyte concentration

Sensitivity : slope of calibration curve

(Larger slope of calibration curve,more sensitive measurement)

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Limit of detection (LOD): “the lowest concentration of analyte in a sample that can be detected”

slopes

C bLOD

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Limit of Quantitation (LOQ)“the minimum injected amount that producesquantative measurements in the target withacceptable precision”

slopes

C bLOQ

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Selectivity:“ability of the method to measure one species of analyte in the presence of other elements or compounds”

Example:

A + Bsample

Signal = mACA + mBCB + SignalblankmA, mB = calibration sensitivity of A, BCA, CB = concentration of A, BSelectivity coefficient: kB,A = mB/mA

k’s vary between 0 (no selectivity) and large number (very selective).

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Calibration methodsBasis of quantitative analysis is magnitude of measured property is proportional to concentration of analyte”

Signal [x] or

Signal = m[x] + signalblank

[x] = (signal-signalblank)/m

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Calibration curve (working or analytical curves)

Instrument response(signal)

Slope mSignalblank

LOD

LOQ

LOL

Dynamic Range

[x]