First evidence of nitroaromatic compounds in indoor dust: determination of nitrophenols, nitroguaiacols, and nitrocatechols by microwave-assisted extraction combined with solid-phase microextraction gas chromatography-tandem mass spectrometry

Nitroaromatic compounds, encompassing nitrophenols (NPs), nitrocatechols (NCs), and nitroguaiacols (NGs), have garnered significant attention due to their potentially harmful effects on human health and the environment. However, to date, no studies have been conducted on the analysis of these compounds in indoor dust. In order to address this lacuna, an analytical procedure was developed for the determination of NPs, NCs, and NGs in indoor dust. The proposed method is based on the extraction of target analytes by microwave assisted extraction (MAE) with an eco-friendly water-ethanol (50:50, v/v) mixture, employing a MAE modified setup based on smaller containers that reduced both sample and solvent volumes and enabled up to 96 simultaneous extractions. The MAE extract was then derivatized using chloroformates, a strategy that yielded mass spectra with enhanced sensitivity and specificity compared to those obtained thorough conventional acetic anhydride derivatization. The resulting derivatives were subsequently isolated by solid-phase microextraction (SPME) and analyzed by gas chromatography-tandem mass spectrometry (GC–MS/MS). Key parameters for derivatization, MAE, and SPME were optimized by means of the multivariate approach of experimental design and factorial analysis. Method validation demonstrated satisfactory LLOQ values (0.5 ng/mL for mononitro compounds and 10 ng/mL for dinitro compounds), accuracy (ranging from 81 to 120 %), and precision (RSD% between 0.2 and 12.6 %). The application of the proposed method to real samples revealed, for the first time, the presence of 4-NP (0.059–0.116 µg/g), 4-NG (0.064–0.093 µg/g), 4-NC (0.014–0.156 µg/g), and 4-Me-5-NC (0.010–0.048 µg/g) in indoor dust, thereby underscoring the potential role of this matrix as a pathway for human exposure to these contaminants.