Post column derivatization requires a continuous supply of reagent, and therefore it necessitates the use of a second, low pressure pump connected by means of a confluence point after the column and in front of the detector.
Post-column derivatization following separation on a monolithic column has been published recently (Adcock 2007). The authors designed an instrument based on a flow injection scheme, served with three Milligat pumps. A pair of pumps upstream from the injection valve created an elution gradient, while the third pump supplied a derivatization reagent in postcolumn fashion. This innovative work allowed excellent separation of opiate alkaloids and biogenic amines for their assay in urine, using chemiluminiscence detection.