Determination of pharmaceuticals in sewage sludge and biochar from hydrothermal carbonization using different quantification approaches and matrix effect studies

Abstract

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.

Pharmaceutical load in sewage sludge and biochar produced by hydrothermal carbonization

“…No removal rates are given for diclofenac because matrix effects caused a high LOQ in this biochar sample impeding to derive removal rates. Sulfamethoxazole showed decreased recovery in sewage sludge, which was reported previously (vom Eyser et al, 2015).…”

“…The single calibration steps were 10-20-40-80-160-320-640-1028-2056-5120 μg/kg DM . Sample aliquots of 1 g were mixed with Ottawa sand, transferred to 11-mL stainless steel cartridges, which were filled with Ottawa sand and extracted using pressurized liquid extraction (PLE) (Dionex ASE200, Thermo Fisher GmbH, Idstein, Germany) according to an existing method (vom Eyser et al, 2015) for the pharmaceuticals except propyphenazone, 4-AA and MAA. In short: The solvent methanol extracted the compounds in one cycle within 15 min at 100°C and 100 bar.…”

“…A Waters Atlantis T3 column (100 × 2.1 mm, 3 μm, Waters GmbH, Eschborn, Germany) was applied for chromatographic separation. Chromatographic and MS parameters are given elsewhere (vom Eyser et al, 2015) except for the pyrazolones. The supplementary material lists all chromatographic and mass spectrometric parameters (S 3).…”

“…However, these results have not been transferred to sewage sludge yet. Recently, we (vom Eyser et al, 2015) developed a method to determine pharmaceuticals in sewage sludge and biochar.…”

Quantitative mass spectrometry methods for pharmaceutical analysis

“…This methodology is often used when the sample matrix already contains trace elements of the analyte prior to spiking. By adding a dilution series, the actual concentration can be calculated by extrapolating the calibration curve to zero [19,146,147]. Sometimes, different samples are pooled together to average interferences or a matrix is searched wherein the analytes are not present or at least below the detection limit [148,149].…”