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).