As quality control samples, SRM 1950 in one to ten dilution and a solvent QC comprising all target analytes at 1 µM (median of 186 ng/mL, metabolites) and approximately 100 ng/mL (xenobiotics) were analyzed throughout the sequence. Moreover, 10 μL of each urine sample was pooled together for the Austrian and Nigerian samples separately. This pooled urine sample from the Austrian study was measured every nine injections while measuring these samples. The Nigerian pooled urine sample was injected repeatedly with a maximum of nine individual samples in between to check the instrument performance. Solvent blanks (pure reconstitution solvent) and system blanks (200 μL water extracted according to the sample preparation protocol) were measured to correct for contaminations in the system and during the sample preparation.