Trace analysis of quinapril and its active metabolite, quinaprilat, in human plasma and urine by gas chromatography-negative-ion chemical ionization mass spectrometry.

A highly specific and sensitive method for the simultaneous determination of quinapril and its active metabolite, quinaprilat, in human plasma and urine by gas chromatography-negative-ion chemical ionization mass spectrometry is described. Quinapril and quinaprilat were extracted from human plasma and urine by using a Bond-Elut C18 cartridge. The plasma or urine extract was treated with pentafluorobenzyl bromide followed by trifluoroacetic anhydride to convert quinapril and quinaprilat into their pentafluorobenzyl-trifluoroacetyl derivatives, which were analysed by a selected-ion monitoring method using deuterium-labelled internal standards. The limits of quantitation for both quinapril and quinaprilat were 0.05 ng/ml in plasma and 0.5 ng/ml in urine. The proposed method is applicable to pharmacokinetic and clinical pharmacological studies with satisfactory reliability.