Determination of quinapril and quinaprilat by high-performance liquid chromatography with radiochemical detection, coupled to liquid scintillation counting spectrometry

Quinapril and quinaprilat concentrations were determined in perfusate, urine, and perfusate ultrafiltrate using a specific and sensitive reversed-phase high-performance liquid chromatographic procedure with radiochemical detection, coupled to liquid scintillation counting spectrometry. Quinapril and quinaprilat were measured in perfusate and urine after pretreatment with acetonitrile and subsequent centrifugation. Perfusate ultrafiltrate was used as collected. Two quinapril diketopiperazine metabolites, PD 109488 and PD 113413, were separated chromatographically from quinapril, quinaprilat, and from each other. Assay performance for quinapril and quinaprilat was assessed by examining precision and accuracy of the assay over four days. Using a 100-μl sample volume, the limit of quantitation for both 3H-quinapril and 3H-quinaprilat (sp. act. ≈ 2.0 μCi/μg) was 1 ng/ml.