Postcolumn Derivatization Table 1 Figure

Post-column derivatization was the first development of IEC in the area of RP/high performance liquid chromatography (HPLC), in its pioneer period. It took time to develop pre-column derivat-ization concepts which resulted in considerable advantages.

Drawbacks of the post-column techniques (Table 1) are long elution times and the need for costly devices, such as a delivery system for the de-rivatizing reagent (one or more extra pumps); (a) mixing chamber for the column effluent and the re agents); special thermostable reactors (packed bed, air-segmented and/or coil reactors) ensuring the necessary delay for quantitative reactions accompanied with as small band broadening as possible. Last but not least, the mobile phase was probably incompatible with the derivatizing reagent. The preferred mobile phase might be inappropriate for the optimum conditions of derivatization reaction. The early and current stages of post-column methods can be illustrated by elution followed by post-column reaction with ninhydrin (NHYD; Figure 3A), with o-phthaldialdehyde/^-mercaptoethanol (OPA/MCE; Figure 3B), or with 1,2-naphthoqunione-4-sulfonyl chloride (NQS; Figure 3C). All three types of derivatives have been separated in most cases on ion exchange resin columns from the early 1970s. Recent post-column methods are without exception, slow separations (Table 1). However, the efficiency of the recently published methods of NHYD derivatives using short columns is superior, determining 59 compounds in 150 min and 40 compounds in 120 min respectively.

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