CHE 322
TERMS
CHAPTER 3
TERMINOLOGY IN ANALYTICAL CHEMISTRY
CHE 322
A.
TERMS
SAMPLE CONSTITUENTS TERMS
Analyte
An analyte is a species of interest in the sample.
Matrix
The rest of the sample is the matrix
B.
INVESTIGATIVE TERMS
Measurement
A mesurement is the experimental determination of the amount or properties
of an analyte or the sample.
Analysis
Complete process leading to the sought for information (chemical and/ or
physical) about the sample.
Determination
A determination is the results of an analysis.
e.g. concentration, composition, chemical/ physical properties.
CHE 322
C.
TERMS
TERMINOLOY IN ANALYTICAL METHODOLOGY
Technique
A chemical or physical principle that makes the analysis possible.
e.g. Potentiometric titration of HCl by NaOH
Chemical principle ________________________________________
Physical principle ________________________________________
Method
Means of applying a technique for the investigation of a specific analyte, a
specific type of sample, in a specific type of environment, etc…
Procedure
A procedure is an outline of specific instructions for the analysis of a
sample.
Protocol
Detailed procedure with specific requirements that must be strictly adhered
to, for results of an analysis to be acceptable to the agency specifying the
procedure.
CHE 322
TERMS
D.
CLASSIFICATION OF ANALYTICAL TECHNIQUES
D.1
Total analysis techniques
S A  kn A
SA
signal generated by analyte
k
proportitonality constant
nA
number of moles or grams of analyte
Generally, the signal is generated by one or more chemical reaction of the
analyte.
Are the following total analysis techniques?
Titration using an indicator for end point detection?
______
Potentiometric titration?
______
D.2
Concentration techniques
S A  kC A
C A : concentration of analyte
Most concentration techniques rely on an electrical and optical response.
CHE 322
E.
TERMS
CRITERIA FOR SELECTING AN ANALYTICAL METHOD
Requirements of the analysis
E.1
Accuracy
% Error 
obtained  exp ected
 100
exp ected
Relative error
 1%
1%-5%
5%
E.2
Accuracy
High
Moderate
Low
Precision
Agreement between several measurements
How many determinations should one make ideally?
(Precision versus accuracy)
E.3
k
Sensitivity
S A
n A
S A
C A
S A smallest increment in signal that can be measured
n A smallest difference in the amount of analyte that can be detected
Note: Sensitivity should not be confused with detection limit.
Detection limit is the smallest amount of analyte that can be determined with
confidence.
k
CHE 322
E.4
TERMS
Selectivity
S samp  S A  S I  k A n A  k I n I
(1)
S samp  S A  S I  k AC A  k I C I
(3)
k
K A, I  I
kA
A
analyte
I
interferent
K A, I selectivity coefficient
S samp  S A  S I  k A (n A  K A, I n I )
Read example 3.2 in text book
E.5
(3)
Robustness and ruggedness
A robust method is a method that can be applied to analyte in a wide variety
of samples and matrices.
e.g. Reversed-phase gas chromatography can be used for many separations
in industrial and research laboratories.
A rugged method is insensitive to changes in experimental conditions.
e.g. gradual deterioration of the column, small variations in solvent
composition, pH, and temperature, or use of a different batch of the same
stationary phase, perhaps from a different manufacturer.
CHE 322
E.6
TERMS
Scale of operation
What range of samples can be accommodated by method?
Considerations:
1) amount of sample available for analysis
2) concentration of analyte in the sample
3) absolute amount of analyte needed to produce a measurable response/
signal
1 and 2 define scale of operations, 3 determine position within scale
Scale of operations
Figure 3.6 on page 43
Analyte
Concentration
% (w/w)
Sample size and absolute amount
10 g
1g
100 mg
10 mg
1mg
107 %
0.01 %
1 mg
0.1 mg
0.01 mg
0.001 mg
0.0001 mg
Ultratrace
Trace
0.1 %
10 mg
1 mg
0.1 mg
0.01 mg
0.001 mg
Minor
1%
100 mg 10 mg
1 mg
0.1 mg
0.01 mg
Major
10 %
1g
100 mg
10 mg
1 mg
.1 mg
100 %
10 g
1g
100 mg
10 mg
1 mg
macro
meso
Micro
Total analysis technique
Sample size
Concentration techniques have
Lower limit
ppm/ ppb (detection limit)
Upper limit
set by sample and technique characteristics
CHE 322
PRIORITY IN SELECTION OF MEHTOD
1.
2.
3.
4.
Accuracy
Selectivity
Precision
Time, Cost, Expertise
TERMS
CHE 322
TERMS
F. DEVELOPING A PROCEDURE
Compensating for interference  selecting and calibrating equipment 
standardize the method  obtain a representative sample  validate the
method
F.1 Compensating for interferences
Interferent: anything that contributes to the measured signal.
Can be part of the sample or reagent added during analysis
In the absence of interferent
S meas  S A  S reag  kn A  S reag
S meas  S A  S reag  kC A  S reag
S reag obtained from blank
In the presence of interferent
S meas  S A  S I  S reag  k A n A  k I n I  S reag
S meas  S A  S I  S reag  k AC A  k I C I  S reag
F.2
Calibration
Use a standard for which the expected signal/ response is known to
ensure that an instrument or the equipement operates correctly.
F.3
Standardization
Determine the relationship between the magnitude of the signal and
the amount of the analyte.
F.4
Sampling
Representative sample
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F.5
TERMS
Validation
Does the method provide acceptable results?
Use standard sample
Several analysts, different laboratories
Compare with results obtained with a method of known accuracy.
F.6
Quality control and quality insurance
Protocols include
1) Internal QA/QC ensures accuracy and precision
2) External QA/ QC establishes criteria used by an agency to certify a
laboratory
Read p48 EPA's Contract Laboratory
Read page 50 if you care for the quality of US surface waters.
SUGGESTED PROBLEMS
3.2, 3.3, 3.6, 3.8