Biochar-based alternative method for indoor VOCs analysis using thermal desorption tubes and gas chromatography

Urban air quality has become an increasing concern due to the presence of volatile organic compounds (VOCs), which adverse effects on human health and the environment. In indoor environments, particularly in closed rooms, these compounds tend to accumulate due to limited ventilation and the continuous presence of emission sources, intensifying occupational risks and analytical interferences. In this context, the use of thermal desorption (TD) tubes stands out as an efficient preconcentration strategy for VOCs analysis by gas chromatography (GC), while significantly reducing solvent consumption in accordance with green chemistry principles. Therefore, this study evaluated the use of biochar derived from the pyrolysis of dwarf red coconut fiber as a sorbent in thermal desorption tubes for VOCs analysis in laboratory environments. Initially, a comparison of different sorbent materials was performed using a portable thermal desorption system coupled to a GC with a flame ionization detector (HandyTD-GC-FID) to assess biochar's performance relative to commercial adsorbents for the analysis of 37 VOCs, (Indoor Air Standard – Merck). Subsequently, desorption parameters, including temperature, pressure, time, and heating rate, were optimized. The method was then validated using TD followed by comprehensive two dimensional GC coupled with time-of-flight mass spectrometry (TD-GC×GC-TOFMS), assessing performance parameters such as linearity, limits of detection and quantification, accuracy, precision, and applicability to real samples. The results demonstrated that the biochar-based tube exhibited performance comparable to the commercial sorbents Tenax TA, Carbotrap 300, and Carbotrap T420, and superior to Carbopack B, Carbotrap 202, and a triazine-based polymer. Optimization of desorption parameters improved analyte release efficiency and chromatographic resolution, even in the absence of a cryogenic refocusing system. The method showed satisfactory linearity (R² > 0.90) over the range of 0.1 to 40 μg mL-1, with limits of detection and quantification of 0.006 to 1.756 μg mL-1 and 0.018 to 5.321 μg mL-1, respectively. Accuracy was below 30.0% for most compounds, while precision ranged from 4.2% to 20.6% (at 15 μg mL-1). Among the target compounds, 21 VOCs were detected in real samples and 17 were quantified, with concentrations ranging from 0.18 to 5.14 μg mL-1. These results highlight the potential of biochar as an alternative adsorbent for thermal desorption tubes, offering a more sustainable approach to indoor VOC monitoring that aligns with green chemistry principles and the United Nations Sustainable Development Goals.