High-performance liquid chromatographic separation of femtomolar quantities of endogenous carboxylic acids, including arachidonic acid metabolites, as 4-bromomethyl-7-acetoxycoumarin derivatives.

A major limitation of high-performance liquid chromatographic techniques for measuring biologically active eicosanoids has been the inadequate sensitivity of most on-line detection systems. In addition, the availability of a technique suitable for measuring small quantities of non-esterified fatty acids (NEFAs) in plasma would allow longitudinal studies of plasma levels of these lipids in small animals. To improve the sensitivity of detection, the compounds with acyl groups containing carboxylic acids were derivatized with the highly fluorescent compound, 4-bromomethyl-7-acetoxycoumarin. All classes of NEFA and arachidonic acid metabolites, including the cyclooxygenase and lipoxygenase products, and hydroxy acid compounds could be derivatized with this reagent. The derivatized metabolites were separated with a reversed-phase high-performance liquid chromatographic system using a radial compression column and a gradient elution technique. Reproducible measurements of plasma NEFAs from as little as 5 microliters of plasma, and femtomolar concentrations of eicosanoids, could be detected using an on-line fluorescent spectrometer. This improvement in sensitivity should permit the quantification of all eicosanoids, including the leukotrienes, in biologic fluids and the longitudinal measurement of changes in plasma NEFA levels in small animals.