Analysis of phthalate esters and their novel alternatives in indoor dust using comprehensive two-dimensional gas chromatography-time of flight mass spectrometry

A comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOF-MS) method was developed to analyze 25 traditional phthalate esters (PAEs) and 19 novel alternatives in indoor dust samples. PAEs are ubiquitous in indoor environments because they are widely used as plasticizers in a variety of consumer products, and potential health concerns have prompted the need for effective monitoring methods. In this study, dust samples were collected from various indoor settings in a university campus, including classrooms, cafeterias, laboratories, and dormitories, and were subsequently ultrasonically extracted with hexane-dichloromethane (1∶1, v/v) solution for 30 min. This method was chosen to maximize PAE recovery while minimizing potential interference from other compounds present in the dust matrix. Compounds were separated on a Rix-5MS column (30 m×0.25 mm×0.25 μm) as the first dimension, with a Rix-17Sil column (1.39 m×0.25 mm×0.25 μm) serving as the second dimension. The following temperature program was used: 60 ℃ for 1 min, then increasing to 220 ℃ at 20 ℃/min, followed by a further increase to 290 ℃ at 5 ℃/min, with the final temperature held for 8 min; this program was optimized to afford maximum target-compound resolution and sensitivity. The developed method rapidly, accurately, and sensitively detected the target PAEs and their alternatives under the optimal conditions, which included a carrier-gas flow rate of 1.4 mL/min, a modulation period of 4 s, and an injection-port temperature of 250 ℃. The 44 target compounds exhibited highly linear calibration curves across a content range of 1-500 μg/g, with all correlation coefficients exceeding 0.99. The limits of detection (LODs) of the method were determined to lie between 0.57 and 13.0 ng/g, which reflects the high sensitivity of the developed approach. At spiked levels of 1, 10, and 50 μg/g, the recoveries of the analyzed compounds varied from 72.8% to 125%, with relative standard deviations ranging from 1.29% to 14.8% (<i>n</i>=3), which indicates that the method is highly precise and reliable. The developed method was used to analyze PAEs and their alternatives in 40 indoor dust samples, which revealed total contents of between 2.07 and 354 μg/g in dust samples. Di-2-ethylhexyl phthalate (DEHP) emerged as the most frequently detected compound, with contents ranging from "not detected" (nd) to 158 μg/g. The novel alternative, bis(2-ethylhexy) terephthalate (DEHTH), was also detected, with levels ranging from nd to 117 μg/g. Notably, significant differences in the compositions and contents of the PAEs and their alternatives were observed across various indoor environments, which suggests that diverse sources and exposure pathways exist for these compounds, highlighting the necessity for ongoing PAE monitoring and risk assessment in various indoor settings. In conclusion, the developed GC×GC-TOF-MS method provides a powerful tool for comprehensively analyzing PAEs and their alternatives in indoor dust; it is well-suited for the routine monitoring of these compounds owing to its simplicity, rapidity, and robustness. These findings provide valuable insight for future research into the sources and health implications of PAEs in indoor environments, and ultimately support risk assessment and regulatory efforts.