The method was in-house validated for all three matrices according to the European Commission Decision No. 657/2002 . Three independent sample preparations were performed with two weeks between each measurement series. Matrix-matched calibration standards were prepared by dissolving the extracted blank sample matrix in the respective solvent standards after evaporation. The multianalyte standard for calibration was based on the matrix with the highest sensitivity for each analyte. As no certified reference material was available, spiking experiments at 3 the approximate LOQ (limit of quantification defined as a signal-to-noise ratio of 10) and 30 the LOQ were conducted in triplicates. LOQs and LODs (limit of detection defined as a signal-to-noise ratio of 3) and matrix effects in the form of signal suppression or enhancement (SSE evaluated by the ratio of the slope of the matrix-matched calibration and the slope of the solvent calibration) were evaluated once per validation run (n=3). Linearity was assessed by the regression coefficient R 2 (n=3), but as no specific value is stated in the guidelines, a limit of R 2 >0.9 was assumed. Intermediate precisions were calculated as the relative standard deviation between the results of the spiking experiments (n=9). To assess selectivity, matrix blanks and system blanks were prepared in triplicates by extracting sample matrix and LC-MS grade water, respectively, and screened for interfering peaks. Method repeatability (intra-day precision) was evaluated by the repeated measurement of one validation batch (n=6).