Development of a Refrigerant-Free Cryotrap Unit for Pre-Concentration of Biogenic Volatile Organic Compounds in Air

Biogenic volatile organic compounds (BVOCs) are key compounds in atmospheric chemistries, but difficult to measure directly. In this study, a pre-concentration unit combined with gas chromatography-mass spectrometry (GC-MS) was developed for the quantitative analysis of 18 BVOCs in ambient air. The analytes are trapped on an empty silonite-coated tube, which is cooled by a thermoacoustic cooler to cryotrap at −150 °C, and then desorbed by rapid heating to 200 °C. The set-up involves neither the exchange of solid adsorbents nor any further condensation or refocusing steps. Reliable operation is ensured by the thermoacoustic cooler, which neither contains a liquid refrigerant nor requires refilling a cryogen. The pre-concentration unit parameters such as water removal temperature, desorption temperature and desorption time were optimized. All compounds had correlation coefficients that were better than 0.95, and the detection limits were 0.005–0.009 ppbv when the injection volume is 400 mL. The repeatability ranges were 0.9–5.8%. The recoveries were ranged from 81.8% to 93.2%. This new method was applied for the first time to measure ambient BVOCs in suburb Guangzhou in summer 2022. Isoprene concentrations ranged from 0.375 ppbv to 2.98 ppbv. In addition, several extremely low-level monoterpenes (e.g., α-pinene, β-pinene, and D-limonene) were also detected by the method.