Application of Cookson‐type reagents for biomedical HPLC and LC/MS analyses: a brief overview

High‐performance liquid chromatography (HPLC), LC/mass spectrometry (MS) and LC/tandem mass spectrometry (MS/MS) have been widely used for biomedical analyses, in which chemical derivatization is one of the most important methods to increase the sensitivity and selectivity. A Cookson‐type reagent [4‐substituted‐1,2,4‐triazoline‐3,5‐dione (4‐substituted‐TAD)] reacts with the compound bearing a conjugated diene, such as the vitamin D compound, to quantitatively form the stable Diels–Alder adduct. The reagent with a chromophore or fluorophore at the 4‐position of TAD yields a highly responsive adduct for the UV or fluorescence detection, respectively. The Diels–Alder adduct with a Cookson‐type reagent having a permanently charged, proton‐affinitive or electron‐affinitive moiety is sensitively detected by a specific MS analyzer. This paper is a brief overview of the applications of the reagents for biomedical analyses mainly using HPLC or LC/MS(/MS).