Transcript Document

303354
Analytical Chemistry II
Somsak Sirichai
Lectures: Tuesday 1.00-3.00 p.m.
Friday 8.00-9.00 a.m.
C310
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Course Description:
Teach fundamental of instrumentation analysis
 Spectrochemical analysis
UV-VIS, IR, Fluorescence & Phosphorescence,
AA, ICP, X-ray, NMR, MS
 Electrochemical analysis
Potentiometry, Coulometry, Voltammetry
 Chromatographic analysis
GC, HPLC
 Capillary Electrophoresis
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 CE
Khaledi; High Performance Capillary Electrophoresis
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Introduction
Qualitative
analysis
(1)
Analysis
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)
the species to be determinded in the sample
matrix
Matrix-analyte = concomitants
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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 methods
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.
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Types of Instrumental Methods
Signal
Radiation emission
Example Method
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 Method
Radiation 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 Method
Electrical 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
Energy
stimulus
Analytes
(in matrix)
Analytical
response
Example: Spectrophotometry
Data
Encoded
information
Instrument: spectrophotometer
Stimulus: monochromatic light energy
Analytical response: photocell
Data: electrical current
Data processor: current meter
Readout: meter scale
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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
Physical
(light intensity, colour)
Chemical (pH)
Electrical domains
Current
Voltage
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Selecting an Analytical Method
Defining the Problem
A definition requires answers to the following
questions:
1.
2.
3.
4.
What accuracy and precision are required?
How much sample is available?
What is the concentration range of the analyte?
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 of
Instruments; 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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Absolute standard
Deviation (s)
Relative standard
deviation (RSD)
Coefficient of
Variation (CV)
N
s 
2
(
x

x
)
 i
i 1
RSD 
CV 
N 1
s
x
s
x
Standard deviation
of means (sm)
x 100%
sm 
s
N
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Accuracy: determinate errors
(operator, method, instrumental)
% Relative error (%Er)
%E r
xi  xt

x 100
xt
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Sensitivity:
“the ability to detect (qualitative analysis)
or determine (quantitative analysis) small
amounts of an analyte in a sample”
x
S 
C
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”
C LOD
3s b

slope
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Limit of Quantitation (LOQ)
“the minimum injected amount that produces
quantative measurements in the target with
acceptable precision”
C LOQ
10s b

slope
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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+B
sample
Signal = mACA + mBCB + Signalblank
mA, mB = calibration sensitivity of A, B
CA, CB = concentration of A, B
Selectivity coefficient: kB,A = mB/mA
k’s vary between 0 (no selectivity) and
large number (very selective).
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Calibration methods
Basis 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)
Dynamic Range
LOQ
LOD
Signalblank
LOL
Slope m
[x]
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