Acoustic Levitation-Controlled\nDroplets for Contactless\nEnrichment and Sensitive Detection of Volatile Organic Substances\nIntegrated with GC-MS

Analyzing\ntrace-level volatile organic compounds (VOCs)\nremains\nchallenging due to initial sampling and preconcentration limitations.\nInspired by the highly reproducible and constantly renewable electrode\nsurface of dropping mercury electrode (DME), a contactless enrichment\nprocess was first reported by using an acoustic levitation device\nto trap and concentrate VOCs from gas samples onto suspended droplets,\nwhich were then directly transferred into gas chromatography–mass\nspectrometry (GC-MS) for real-time analysis. Compared with traditional\nmethods injection methods, this method achieves a 46-fold increase\nin nicotine peak area. The detection sensitivity was enhanced significantly,\nattributed to the high specific surface area of the droplets and the\naccelerating extraction vibration. Notably, the number of identified\nVOCs from burning cigarettes significantly increased from 17 to 212,\nincluding 22 aromatic compounds with distinct aromas. The remarkable\nversatility of this method was demonstrated by effectively monitoring\nthe dynamic changes of 16 VOCs in environmental tobacco smoke (ETS)\nfollowing cigarette burning, revealing the persistence of these compounds,\neven after 40 min. Moreover, directly analyzing human-exhaled aerosol\nfound that nicotine rapidly decreased while its metabolite cotinine\nincreased, showcasing the potential for tracking human metabolism\nand behavior in vivo. Furthermore, multivariate data analysis of VOC\nprofiles from six cigarette brands allowed for their visual differentiation.\nWith versatility, sensitivity, and the ability to distinguish trace-level\nVOCs in realtime, this method offers promising avenues for environmental\nmonitoring, metabolic studies, and various analytical applications.