1.4 Essential Features of Analytical Chemistry
11
pesticide in drinking water is to be determined, a specimen of the pure pesticide
(or a sample standard containing it) is subjected to an appropriate analytical
process in order to obtain a qualitative and quantitative response that can be
used as a reference in identifying and quantifying the pesticide in the target
object (water). If the "instrument" used is a human sense (e.g. in classical qualitative analysis), then the analyst must previously memorize the response of a
suitable standard.
__ Box 1.S
The typical odour of hydrogen sulphide (H1S) must be known if the presence of sulphide in a
sample is to be identified. For this purpose, the sample is supplied with hydrogen chloride
(HCI), wh ich produces H2S, a volatile compound with a distinctive smell:
Sl- + 2W --7 H 2 Si
sample
In order to recogn ize the odour, the analytical chemist must previously have smelt it. The
odour can be experienced by adding HCI to a solution of sodium sulphide (a standard).
The concentration of copper in an alloy can be quantified by dissolving the sample and
placing and aliquot of the resulting solution in an atomic absorption spectrometer to obtain
an absorbance signal. This piece of information only allows one to confirm the presence of
copper. In order to determine its concentration, one must establish a relation between absorbance and concentration by using standards containing variable amounts of copper in
order to construct a "calibration curve" that is then fitted to an equation of the type
[absorbance) = a + b x [copper concentration)
The absorbance value obtained allows one to calculate the concentration of copper in the
solution and hence its proportion, by weight, in the original sample (alloy).
Consequently, Analytical Chemistry is meaningless unless one or more standards suited to the type of information required are available. One essential goal
of Analytical Chemistry is thus to find and properly use reliable references. Poor
or improperly employed references produce analytical chemical results of
inadequate quality, however suitable the technical means employed and high the
laboratory performance achieved may be.
Analytical chemical standards are discussed in detail in Chap. 3, which is
devoted to traceability (a metrological property to which the standards are
closely related).
1.4 Essential Features of Analytical Chemistry
While definitions must inevitably be strict and austere, they should be completed with a description of all those aspects required to delineate their contents
precisely. Such is the case with the definition of Analytical Chemistry, the current
and foreseeable connotations of which are discussed in the following sections.
11
pesticide in drinking water is to be determined, a specimen of the pure pesticide
(or a sample standard containing it) is subjected to an appropriate analytical
process in order to obtain a qualitative and quantitative response that can be
used as a reference in identifying and quantifying the pesticide in the target
object (water). If the "instrument" used is a human sense (e.g. in classical qualitative analysis), then the analyst must previously memorize the response of a
suitable standard.
__ Box 1.S
The typical odour of hydrogen sulphide (H1S) must be known if the presence of sulphide in a
sample is to be identified. For this purpose, the sample is supplied with hydrogen chloride
(HCI), wh ich produces H2S, a volatile compound with a distinctive smell:
Sl- + 2W --7 H 2 Si
sample
In order to recogn ize the odour, the analytical chemist must previously have smelt it. The
odour can be experienced by adding HCI to a solution of sodium sulphide (a standard).
The concentration of copper in an alloy can be quantified by dissolving the sample and
placing and aliquot of the resulting solution in an atomic absorption spectrometer to obtain
an absorbance signal. This piece of information only allows one to confirm the presence of
copper. In order to determine its concentration, one must establish a relation between absorbance and concentration by using standards containing variable amounts of copper in
order to construct a "calibration curve" that is then fitted to an equation of the type
[absorbance) = a + b x [copper concentration)
The absorbance value obtained allows one to calculate the concentration of copper in the
solution and hence its proportion, by weight, in the original sample (alloy).
Consequently, Analytical Chemistry is meaningless unless one or more standards suited to the type of information required are available. One essential goal
of Analytical Chemistry is thus to find and properly use reliable references. Poor
or improperly employed references produce analytical chemical results of
inadequate quality, however suitable the technical means employed and high the
laboratory performance achieved may be.
Analytical chemical standards are discussed in detail in Chap. 3, which is
devoted to traceability (a metrological property to which the standards are
closely related).
1.4 Essential Features of Analytical Chemistry
While definitions must inevitably be strict and austere, they should be completed with a description of all those aspects required to delineate their contents
precisely. Such is the case with the definition of Analytical Chemistry, the current
and foreseeable connotations of which are discussed in the following sections.