Prospects for development of the method

Subtraction methods are widely used in chromatographic practice, mainly for identifying chromatographic zones in the analysis of unknown mixtures. This is a very important, but not the only, problem that can be solved by use of this method. Subtraction methods can also be successfully employed for solving the following problems (1) demasking of impurity zones, which are often masked by the zone of the principal components (2) concentrating impurities with the use of selective absorbers and (3) determination of the content of components in the overall unseparated zone. 

Simplicity and flexibility are the attractive features of the subtraction method. Despite the utilization of this method in practice it has not been developed thoroughly enough, even for identification purposes. Numerous publications on this method mainly contain, with rare exceptions, a description of its application to several classes of organic compounds, although its practical value essentially depends on how comprehensively the reagent used has been studied (selectivity, interaction with many classes of organic compounds, volatility, maximum temperature of utilization, reaction rate, completeness of reaction under different conditions, side-reactions, etc.). 

The development of the subtraction method requires the elaboration of a systematic method of analysis of organic compounds and the development of techniques for its utilization in capillary chromatography. 

The method can be substantially simplified by using selective volatile reagents. This aspect is also extremely promising in particular, its utilization makes the two-stage version easier to achieve. Further development of the method for concentrating impurities, including those in the environment, is also of interest. 

The examples considered in this chapter indicate that further development of the method will be of practical value. 

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