Atropine is a racemic mixture of d- and l-hyoscyamine, but only l-hyoscyamine is the effective ingredient. In this study, a new, sensitive, stable, and selective LC/MS assay was developed for the determination of l-hyoscyamine and applied to a clinical study. The parent-product (m/z) transition pair of l-hyoscyamine was 290.1 → 124.1. Chromatographic separations were performed using a chiral MZ column (250 mm × 4.6 mm, 5.0 μm) by a stepwise gradient elution mode with n-hexane, isopropanol, and diethylamine as mobile phases. l-Hyoscyamine in human plasma was extracted by liquid-liquid extraction. This assay displayed a good linearity over a concentration range of 20.0-400 pg/mL for l-hyoscyamine. The accuracy of the validation assay for l-hyoscyamine ranged from -2.7% to 4.5%, and the precision was within 6.3% coefficient of variation. l-Hyoscyamine in human plasma remained stable at different storage conditions. The method has been successfully applied to plasma samples obtained from a safety study in humans.
Keywords: LC-MS/MS; atropine; chiral column; l-hyoscyamine.
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