Post-column derivatization increase sensitivity and selectivity, illustrating the versatility of the post-column derivatization (PCD) instrumentation for practical analysis. Reaction flow high performance liquid chromatography columns for methods employing post column derivatization (PCD). In reaction flow post column derivatization (RF-PCD) the derivatization reagent(s) are pumped against the flow of mobile phase into either one or two of the outer ports of the reaction flow column where it is mixed with column effluent inside a frit housed within the column end fitting.

This technique allows for more efficient mixing of the column effluent and derivatization reagent(s) meaning that the volume of the reaction loops can be minimized or even eliminated altogether.

PHRED™ is a compact unit placed between the HPLC column and the detector to perform on-line post-column continuous photolytic derivatization to increase the sensitivity and/or selectivity of response of fluorescence, ultraviolet, electrochemical, and chemiluminescence detectors. "PHRED"TM consists of a lamp holder, a 254 nanometer low pressure mercury lamp, and a holder for the knitted reactor coils (KRCs). The KRCs are especially designed to fit into "PHRED" and their material of construction (PTFE) is transparent to the 254 nm uv light.

This technique has been applied successfully to the analysis of a wide range of compounds including aflatoxins and pesticides.