Analytical Principles

Reliable identification may require confirmation by a method with different selectivity or employing a different analytical principle. 

Fig. 33. Illustration of the steps of signal generation for different analytical principles...

Numerous methods based on different analytical principles have been offered for the measurement of dehydrogenase reactions. Most reliable and simple are spectrophotometric procedures ( optical test ) founded on the assay of one of the participating coenzymes (or substrates). 

The analytic principles that have been applied to accumulate air quality data are colorimetry, amperometry, chemiluminescence, and ultraviolet absorption. Calorimetric and amperometric continuous analyzers that use wet chemical techniques (reagent solutions) have been in use as ambient-air monitors for many years. Chemiluminescent analyzers, which measure the amount of chemiluminescence produced when ozone reacts with a gas or solid, were developed to provide a specific and sensitive analysis for ozone and have also been field-tested. Ultraviolet-absorption analyzers are based on a physical detection principle, the absorption of ultraviolet radiation by a substance. They do not use chemical reagents, gases, or solids in their operation and have only recently been field-tested. Ultraviolet-absorption analyzers are ideal as transfer standards, but, as discussed earlier, they have limitations as air monitors, because aerosols, mercury vapor, and some hydrocarbons could, interfere with the accuracy of ozone measurements made in polluted air. 

The overall process from concept to validated method is illustrated on Page 4 (Figure 1). Once an appropriate analytical principle has been selected and the method performance criteria defined, the actual method development process can begin. Usually, this phase is carried out using pure materials and limited samples that are known, or assumed, to be homogeneous. 

Examining the Limits of Physical Theory Analytical Principles and Logical Implications Erkki J. Brandas3... 

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