Stability
The stability of plasma and urine samples were evaluated at three different QC concentration levels (LQC, MQC and HQC, n = 3 for each level); the conditions were freeze–thaw stability, long-term stability, short-term stability, and post preparative stability in an autosampler. The evaluation of stability under freeze–thaw condition was carried out over five cycles of − 80 °C for at least 12 h of each cycle. Long-term stability was analyzed after storing the samples at − 80 °C. Short-term stability of each analyte, for up to 8 h during processing on the bench at room temperature, was also evaluated. For evaluation of post-preparative stability, the extracted samples were stored at ambient temperature (4 °C) in an autosampler for 24 h. The analyte was considered as a stable sample when the average percentage of accuracy of the QC sample was in the range of 85–115% and the %CV was not over 15%.