To prepare the matrix-matched standards, urine from a female volunteer on a defined diet (where specific food-related exposures were minimized) was collected for three days and stored at -80°C. The sample preparation was performed according to . Briefly, 200 μL urine were combined with 10 μL internal standard mixture and 790 μL ACN/MeOH (1:1 v/v). After sonication for 10 min at 4°C, the samples were incubated for 2 h at -20°C and centrifuged at 18,000 x g for 10 min at 4°C. The supernatant was transferred to a CentriVap Vacuum concentrator (Labconco) and evaporated overnight at 4°C. The dried urine was then reconstituted with 200 μL of the respective solvent standard solution (seven concentrations). After a final centrifugation step, the samples were transferred to amber glass vials with a 200 μL insert. Several blank extractions (process blanks) where the 200 μL urine was replaced with 200 μL water were performed to consider potential contaminants throughout the sample preparation process. For the matrix-adjusted evaluation, a "blank urine" sample was prepared by extracting urine and reconstituting it in 200 μL of 10% ACN. This was necessary to evaluate possible contaminations in the urine "blank" used to prepare the matrix-matched multianalyte standard. To assess sensitivity differences in naturallycontaminated biological samples, spot urine (n=24), collected from female volunteers in Nigeria was prepared according to the procedure outlined above.