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Producing valuable biochar from waste materials using thermal processes like hydrothermal carbonization (HTC) has gained attention in recent years. However, the fate of micropollutants present in these waste sources have been neglected, although they might entail the risk of environmental pollution. Thus, an HPLC-MS/MS method was developed for 12 pharmaceuticals to determine the micropollutant load of biochar, which was made from sewage sludge via HTC within 4 h at 210 °C. Pressurized liquid extraction was applied to extract the compounds. Because of the high load of co-extracted matter, matrix effects in HPLC-MS/MS were investigated using matrix effect profiles. Interfering compounds suppressed 50% of the phenazone signal in sewage sludge and 70% in biochar, for example. The quantification approaches external calibration, internal standard analysis, and standard addition were compared considering recovery rates, standard deviations, and measurement uncertainties. The external analysis resulted in decreased or enhanced recovery rates. Spiking before LC-MS/MS compensated instrumental matrix effects. Still, recovery rates remained below 70% for most compounds because this approach neglects sample losses during the extraction. Internal standards compensated for the matrix effects sufficiently for up to five compounds. The standard addition over the whole procedure proved to compensate for the matrix effects for 11 compounds and achieved recovery rates between 85 and 125%. Additionally, results showed good reproducibility and validity. Only sulfamethoxazole recovery rate remained below 70% in sewage sludge. Real sample analysis showed that three pharmaceuticals were detected in the biochar, while the corresponding sewage sludge source contained 8 of the investigated compounds.

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