Bioanalytical method validation

The bioanalytical method for trandolapril and trandolaprilat was validated for specificity, linearity, the lower limit of quantification (LLOQ), precision, accuracy, recovery, and stability based on the US Food and Drug Administration (FDA) Bioanalytical Method Validation Guidance for Industry. No significant interference peaks were observed in blank plasma (Figure S1). The assay showed excellent linearity (r ² > 0.999) over the concentration range of 10–3000 pg/ml and an LLOQ of 10 pg/ml for both trandolapril and trandolaprilat (Figure S2). The precision, accuracy, recovery, matrix effect, and stability were evaluated by analyzing QC samples at three concentrations (30, 300, and 1000 pg/ml) with five replicates each. The overall precision and accuracy were within the ranges of 3.8–13.3% and 82.7–111.1%, respectively, for both analytes (Table S4). The recovery and matrix effect for both analytes ranged from 84.5% to 110.2% and from 83.7% to 106.5%, respectively (Table S5). Both trandolapril and trandolaprilat were stable after the processed samples were kept in an autosampler at 4°C for 48 h or after 3 successive freeze (−20°C) and thaw cycles of the QC samples (Table S6).