Page 39 - Vogel's TEXTBOOK OF QUANTITATIVE CHEMICAL ANALYSIS

FACTORS AFACTING THE CHOICE OF ANALYTICAL METHODS 1.9

a given determination. This will require careful consideration of the following
criteria.
(a) The type of analysis required: elemental or molecular, routine or occasional.
(b) Problems arising from the nature of the material to be investigated,
e.g. radioactive substances, corrosive substances, substances affected by
water.
(c) Possible interference from components of the material other than those of
interest.
(d) The concentration range which needs to be investigated.
(e) The accuracy required.
(f) The facilities available; this will refer particularly to the kinds of
instrumentation which are at hand.
(g) The time required to complete the analysis; this will be particularly relevant
when the analytical results are required quickly for the control of a
manufacturing process. This may mean that accuracy has to be a secondary
rather than a prime consideration, or it may require the use of expensive
instrumentation.
(h) The number of analyses of similar type which have to be performed; in
other words, does one have to deal with a limited number of determinations
or with a situation requiring frequent repetitive analyses?
(i) Does the nature of the specimen, the kind of information sought, or the
magnitude of the sample available indicate the use of non-destructive
methods of analysis as opposed to the more commonly applied destructive
methods involving dissolution of the sample (possibly in acid) prior to the
application of normal analytical techniques?
Some information relevant to the choice of appropriate methods is given in
condensed form in Table 1.1, which is divided into three sections: the 'classical'
techniques; a selection of instrumental methods; some 'non-destructive' methods.

Table 1.1 Conspectus of some common quantitative analytical methods
Method Speed Relative Concentration Accuracy
cost range (pC)*

Gravimetry S L 1-2 H
Titrimetry M L 1-4 H
-
Coulometry S-M L-M 1-4 H
Voltammetry M M 3-10 M
Potentiometry M-F L- M 1-7 M
Spectrophotometry M-F L-M 3-6 M
Atomic spectrometry F M-H 3-9 M
Emission (plasma) spectrometry F H 5-9 M
Chromatography (GLC; HPLC) F M-H 3-9 M
Neutron activation
X-ray fluorescence
1
* pC = log,,--- where Concentration is expressed in moles per litre.
Concn '
- - - - - - -
t Concentration range kas little significance: detection values are (a) 10-5-10-'2 g; (h) 10-3-10-6 g.
Abbreviations: F, Fast; H, High; L, Low; M, Moderate; S, Slow.