| Abstract: | A liquid chromatographic—mass spectrometric method is described for the determination of a cysteine protease inhibitor (E64C) and its ethyl ester in mouse serum and muscle samples. The compounds in the sample, after deproteinization and solid-phase extraction, were separated by isocratic reversed-phase high-performance liquid chromatography and detected by on-line mass spectrometry. The use of an aqueous mobile phase containing methanol and 30 mM ammonium trichloroacetate provided abundant protonated molecular ions of the compounds in the atmospheric pressure chemical ionization interface of the detection system. The method permitted the quantitative determination of the inhibitors without internal standards in the biological matrices. The detections limits for the compounds, in the selected-ion monitoring mode, were 10–15 pmol on-column, at a signal-to-noise ratio of 5. |
