250
6 Quantitative Aspects of Analytical Chemistry
amount or concentration of analyte that produces it. Except in titrimetric
standardization, such a relationship is derived by using standards containing the
analyte (see Box 6.2).
Standards and calibration are two crucial concepts in Quantitative Analysis.
Accordingly, the most important classification of CMPs for quantitative purposes is based on them (see Sect. 6.1.5).
[ 6.1.4 Classical and Instrumental Quantitative Analysis
The distinction between these two types of analysis is not a categorical one as it
rests on historical rather than on scientific or technical considerations. As can be
seen from Fig. 1.21, both types of analysis can be used for quantitative purposes.
Classical quantitative analysis employs the burette and the balance - two
instruments which have been in use for centuries- to implement the analytical
gravimetric and titrimetric technique, respectively. Both can rely on human
senses to make measurements. With former (two-pan) balances, human sight
was used to directly read out the mass indication for the object being weighed;
in modern balances, the mass is directly displayed as a digital readout. In classical titrimetries, human sight is used to
(a) zero the burette,
(b) stop the addition of titrant when the visual indicator changes colour, and
(c) read the titrant volume used off the millimetric scale on the burette.
In modern titrimetries, an instrumental system is used to identify the titration
end-point and the titrant volume used is supplied in digital form by the autoburette itself. As can be seen from Fig. 6.2, the interface between these two types
of analysis is rather diffuse.
Instrumental quantitative analysis relies on qualitative information obtained in
the second step of a CMP by using instruments other than the balance and the
burette. An optical (e.g. molecular or atomic spectroscopy), electroanalytical
(e.g. potentiometry, polarography, coulometry, anodic stripping voltammetry),
thermal (e.g. differential thermal analysis, thermogravimetry), radiochemical
(e.g. neutron activation, isotope dilution), magnetic (e.g. nuclear magnetic
resonance) or mass technique (e.g. mass spectrometry) can be used for this
purpose. Because they use on-line coupled detectors, gas and liquid chromatographs, and capillary electrophoretic systems, can also be considered instruments (see Boxes 5.16 and 5.17). Because the type of response obtained varies
depending on whether or not the instrument is coupled on-line to a separation
system, the signal will call for a specific quantitative treatment (see Fig. 6.2).
Not all instrumental techniques are equally applicable to the three basic types
of analysis (qualitative, quantitative and structural). Figure 6.3 classifies the better known instrumental techniques into three categories according to whether
they are preferentially used for qualitative or quantitative purposes. This is
obviously a generalization and specific situations require using each technique
in a way different from that depicted in Fig. 6.3.
6 Quantitative Aspects of Analytical Chemistry
amount or concentration of analyte that produces it. Except in titrimetric
standardization, such a relationship is derived by using standards containing the
analyte (see Box 6.2).
Standards and calibration are two crucial concepts in Quantitative Analysis.
Accordingly, the most important classification of CMPs for quantitative purposes is based on them (see Sect. 6.1.5).
[ 6.1.4 Classical and Instrumental Quantitative Analysis
The distinction between these two types of analysis is not a categorical one as it
rests on historical rather than on scientific or technical considerations. As can be
seen from Fig. 1.21, both types of analysis can be used for quantitative purposes.
Classical quantitative analysis employs the burette and the balance - two
instruments which have been in use for centuries- to implement the analytical
gravimetric and titrimetric technique, respectively. Both can rely on human
senses to make measurements. With former (two-pan) balances, human sight
was used to directly read out the mass indication for the object being weighed;
in modern balances, the mass is directly displayed as a digital readout. In classical titrimetries, human sight is used to
(a) zero the burette,
(b) stop the addition of titrant when the visual indicator changes colour, and
(c) read the titrant volume used off the millimetric scale on the burette.
In modern titrimetries, an instrumental system is used to identify the titration
end-point and the titrant volume used is supplied in digital form by the autoburette itself. As can be seen from Fig. 6.2, the interface between these two types
of analysis is rather diffuse.
Instrumental quantitative analysis relies on qualitative information obtained in
the second step of a CMP by using instruments other than the balance and the
burette. An optical (e.g. molecular or atomic spectroscopy), electroanalytical
(e.g. potentiometry, polarography, coulometry, anodic stripping voltammetry),
thermal (e.g. differential thermal analysis, thermogravimetry), radiochemical
(e.g. neutron activation, isotope dilution), magnetic (e.g. nuclear magnetic
resonance) or mass technique (e.g. mass spectrometry) can be used for this
purpose. Because they use on-line coupled detectors, gas and liquid chromatographs, and capillary electrophoretic systems, can also be considered instruments (see Boxes 5.16 and 5.17). Because the type of response obtained varies
depending on whether or not the instrument is coupled on-line to a separation
system, the signal will call for a specific quantitative treatment (see Fig. 6.2).
Not all instrumental techniques are equally applicable to the three basic types
of analysis (qualitative, quantitative and structural). Figure 6.3 classifies the better known instrumental techniques into three categories according to whether
they are preferentially used for qualitative or quantitative purposes. This is
obviously a generalization and specific situations require using each technique
in a way different from that depicted in Fig. 6.3.