Prechromatographic derivatization

All cases involve prechromatographic derivatizations which introduce a chromo-phore leading to the formation of strongly absorbing or fluorescent derivatives... 

There has for some years been a considerable backlog in the development of practicable prechromatographic methods [5]. It is becoming more and more recognized that the future direction to be taken by trace analysts is to make improvements in the extraction, enrichment and clean-up of the sample and in the optimization of derivatization. It is only in this way that it is possible to employ the sensitive chromatographic techniques optimally for the solution of practically relevant problems. 

Table 10 Selection of prechromatographic derivatizations involving oxidation and reduction reactions.

Although the reagent itself is not fluorescent an excess of NBD-chloride can interfere in quantitative analysis. In such cases it should be checked whether prechromatographic derivatization produces better results [3, 4]. The reaction products can then be separated on polyamide layers. 

The reagent can also be employed for prechromatographic derivatization by overspotting [6] or dipping [5]. 

The first part of the book consists of a detailed treatment of the fundamentals of thin-layer chromatography, and of measurement techniques and apparatus for the qualitative and quantitative evaluation of thin-layer chromatograms. In situ prechromatographic derivatization techniques used to improve the selectivity of the separation, to increase the sensitivity of detection, and to enhance the precision of the subsequent quantitative analysis are summarized in numerous tables. 

Prechromatographic derivatization reactions re usually favored when it is desired to modify the properties of the sample to enhance stability during measurement (i.e., minimize oxidative and catalytic degradation, etc.), to improve the extraction efficiency of the substance during sample cleanup, to improve the chromatographic resolution, or to simplify the optimization of the reaction conditions [698-702]. As both pre- and postchromatographic methods enhance the sensitivity and selectivity of the detection process a choice between the two methods will usually depend on the chemistry involved, ease of optimization, and which method best overcomes matrix and reagent interferences. 

---