A liquid chromatographic-tandem mass spectrometric method (LC-MS/MS) for quantifying amlodipine in human plasma was developed and validated. Sample preparation was based on liquid-liquid extraction using NaOH and a mixture of ethyl acetate/hexane (80/20; v/v). Chromatography was performed on a C-18 analytical column and the retention times were 1.9 and 3.0 min for amlodipine and nimodipine (internal standard), respectively. The ionization was optimized using ESI(+) and enhanced selectivity was achieved using tandem mass spectrometric analysis via two MRM functions, 409 --> 238 and 418 --> 343 for amlodipine and nimodipine. The calibration curve ranged from 0.2 to 20.0 ng/mL. The inter-day precision and accuracy and the relative standard deviation (RSD) were <15%. The analyte was shown to be stable over the time-scale of the whole procedure. The robustness of the method was demonstrated by the good reproducibility of the results obtained during the analysis of clinical samples.
A simple, sensitive and specific liquid chromatography-tandem mass spectrometry method for the quantification of bromopride I in human plasma is presented. Sample preparation consisted of the addition of procainamide II as the internal standard, liquid-liquid extraction in alkaline conditions using hexane-ethyl acetate (1 : 1, v/v) as the extracting solvent, followed by centrifugation, evaporation of the solvent and sample reconstitution in acetonitrile. Both I and II (internal standard, IS) were analyzed using a C18 column and the mobile-phase acetonitrile-water (formic acid 0.1%). The eluted compounds were monitored using electrospray tandem mass spectrometry. The analyses were carried out by multiple reaction monitoring (MRM) using the parent-to-daughter combinations of m/z 344.20 > 271.00 and m/z 236.30 > 163.10. The areas of peaks from analyte and IS were used for quantification of I. The achieved limit of quantification was 1.0 ng/ml and the assay exhibited a linear dynamic range of 1-100.0 ng/ml and gave a correlation coefficient (r) of 0.995 or better. Validation results on linearity, specificity, accuracy, precision and stability, as well as application to the analysis of samples taken up to 24 h after oral administration of 10 mg of I in healthy volunteers demonstrated the applicability to bioequivalence studies.
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