Chromatograph post-column derivatization systems

In post-column derivatization the chromatographic system is modified to allow the reagent to mix with the column eluent, give the reaction mixture sufficient time to complete and finally pass the reaction mixture to the detector. 

The detection technique which perhaps has the most potential for trace analysis is post-column derivatization. This is based on the formation of reaction products immediately after column elution and prior to detection. The advantage of such a system is that the samples can be chromatographed directly without the need for prior reaction. Post-column reactions can be very selective, permitting only certain solutes to form derivatives for analysis. These derivatives usually absorb strongly in the UV-visible region or they fluoresce. 

Post-column derivatization does not merely require the selection of the most appropriate reagent to react with the solute to render it detectable, but also involves the modification of the chromatographic system to allow the reaction to take place prior to entering the detector. This necessitates the insertion of a post column reactor between the column and the detector. Such a reactor can easily interfere with the resolution obtained from the column and consequently the reactor system must be designed with some care to... 

LC Many solutes do not exhibit UV absorption or fluorescence, they can be converted in UV absorbing or fluorescent derivatives by pre or post column derivatization. The procedure has a wider range than in GC since the reaction can be performed following separation. When precolumn derivatization is carried out the chromatographic system is obviously different to the one selected for the nonderivatized solutes. 

FI liquid-liquid extraction systems may be coupled to gas and liquid chromatographs in all the three modes presented in Sec. 3.4.6. The objectives for the separation may involve sample cleanup or/and preconcentration for gas and liquid chromatography, but also post-column derivatization for the latter, in fact most applications in the latter field belong to this category. 

High detection sensitivity by absorbance, fluorencence or electrochemical response can be obtained in liquid chromatography provided that the solutes contain structural elements with such activity. If this is not so, detectability can be achieved by pre- or post-column derivatization or, as a third possibility, by ion-pair-mediated indirect detection. In this case, a counter-ion with detector response is added to the chromatographic system or supplied in a post-column extraction system (see Chapter 17). 

A significant advance in post-chromatographic derivatization to fluorescent products came with the introduction of fluorescamine by Udenfriend s group [150], and this was applied to a post-column system by Stein ei al [151], leading to very much greater sensitivity of... 

Hsieh, J.Y.-K. Lin, L. Matuszewski, B.K. High-throughput liquid chromatographic determination of rofecoxib in human plasma using a fully automated on-line solid-phase extraction system, J.Liq.Chromatogr.Rel.TechnoL, 2001, 24, 799-812. [LOQ 0.5 ng/mL plasma post-column photochemical derivatization fluorescence detection SPE]... 

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