Analysis of ethylene glycol (EG) and diethylene glycol (DEG) in oral liquid products using gas chromatography in tandem with Orbitrap spectrometer (GC-Orbitrap).

A selective GC-Orbitrap method has been developed for analysing ethylene glycol (EG) and diethylene glycol (DEG) in four different categories of oral liquid products: Western medicines (WM), traditional medicines (TM), health supplements (HS) and Chinese proprietary medicines (CM). These glycols were chemically ionised to their respective deprotonated ions using methane gas in negative mode and analysed by targeted selected ion monitoring (t-SIM), maintaining a mass error window of ±5 ppm. Internal calibration was performed using matrix-assisted standard solutions ranging from 5 to 100 µg/mL, with 1,4-butanediol-2,2,3,3-D₄ serving as the internal standard (IS). The limits of detection and quantification for both glycols (1.0 µg/mL; 3.0 µg/mL) are comparable with those achieved using gas chromatography tandem with triple quadrupole mass spectrometer (GC-MS/MS) at 0.4 µg/mL and 1.0 µg/mL, respectively. Results showed that most samples were free of EG and DEG. The trace levels of EG and/or DEG detected were below the safety limit of 0.1 % w/w. This methodology not only resolves the false positive identification issues previously encountered with gas chromatography-flame ionisation detection (GC-FID) but also demonstrates broader applicability across different sample matrices, such as oral gel, as evidenced in this study.