Complementary liquid and gas chromatographic-mass spectrometric methods for detecting residual impurities in Cyrene, a sustainable bio-derived solvent

Abstract

Cyrene™ (dihydrolevoglucosenone) is a biomass derived solvent, which has generated significant interest as an attractive green alternative to traditional dipolar aprotic solvents. However, as with other bio-derived solvents, residual impurities from the production process can be difficult to fully remove from the final commercial product, limiting potential applications. A combined liquid chromatography-diode array UV absorbance-electrospray ionisation mass spectrometric (LC-DAD-ESI-MS) method is presented for the simultaneous analysis of residual process-derived impurities in commercially sourced Cyrene, allowing detection of UV-active compounds via diode array detection and non-UV-active compounds via mass spectrometry. Chromatographic separation of Cyrene from residual impurities was achieved in under 12 minutes using a gradient reversed-phase separation, with combined UV absorbance and MS detection, allowing for the determination of the three most abundant residual impurities in Cyrene, namely levoglucosenone (LGO), 2-methoxyphenol (2MP) and sulfolane. Limits of detection (LOD) were 0.02 mg L⁻¹ for both LGO and 2MP by UV absorbance, and 0.27 mg L⁻¹ for sulfolane by ESI-MS. Intra-day and inter-day precision expressed as relative standard deviation (RSD), were always less than 6%, and the method showed excellent linearity, R² ≥ 0.9954, over a concentration range of 0.31–20.00 mg L⁻¹ for all three major impurities. Further for inter-method comparison a complimentary gas chromatography-mass spectrometry (GC-MS) method was developed for the same target Cyrene impurities using a DB-WAX Ultra Inert capillary column. Limits of detection (LOD) were 0.13 mg L⁻¹ for LGO, 0.00707 mg L⁻¹ for 2MP, and 0.11 mg L⁻¹ for sulfolane. For commercial Cyrene samples the two methods provided cross-validatory comparative results for the three impurities of between 3% and 9% of each other when using the external calibration method. This study therefore represents the first fully validated quantitative analysis of LGO, 2MP, and sulfolane in commercial Cyrene using complementary LC-DAD-ESI-MS and GC-MS methods.