A stable isotope assay for phenprocoumon and its metabolites.

A gas chromatographic/mass spectrometric assay for quantifying phenprocoumon and its 4'-, 6-, 7- and 8-hydroxy metabolites in microsomal preparations is described. This assay which uses deuterium-labeled analogs of the phenprocoumon metabolites as internal standards has a lower limit of quantitation of 20 ng ml-1. Diazomethane is used to derivatize both metabolites and parent compound yielding along with the expected 4-methoxy derivative a minor amount of the 2-methoxychromone. Resolution of the methylated metabolites is accomplished by capillary gas chromatography.