Distillation-Assisted Determination of Ethanol in Exhaled Breath Using an Oxygen-Enhanced Gas Curtain Plasma (GCP) Ion Source with High-Field Asymmetric Ion Mobility Spectrometry (FAIMS)

Recent progress in exhaled breath analysis offers a promising noninvasive alternative to blood sampling for clinical and forensic applications. This study presents an oxygen-enhanced gas curtain plasma (GCP) ion source coupled with high-field asymmetric ion mobility spectrometry (FAIMS) for detecting breath alcohol. Exhaled breath condensates were collected from six fasting volunteers before and six hours after alcohol intake, then analyzed by direct GCP-FAIMS and micro-distillation, with mass spectrometry for verification. After alcohol ingestion, the intensity of the ethanol radical cation [C2H5OH]+ (m/z 46) significantly increased from 3 cps to 34 cps, accompanied by enhanced signals of related ions including [NH4+·H2O]+ (m/z 36) and [C4H8O]+ (m/z 72). Micro-distillation further improved spectral clarity and revealed well-resolved ethanol monomer and dimer ions, with compensation voltages matching ethanol standards, confirming impurity removal. The coupled system exhibited good detection sensitivity with a limit of detection (LOD) of 0.318 ppm (m/v) for the protonated ethanol dimer, a limit of quantification (LOQ) of 1.059 ppm (m/v), and a correlation coefficient (R2) of 0.9843. The method also showed good reproducibility with a relative standard deviation of 13.2% for the ethanol monomer signal and 6.5% for the [NH4+·H2O]+ signal. These results demonstrate the proof-of-concept feasibility of the oxygen-enhanced GCP-FAIMS system for ethanol detection in exhaled breath condensate, supporting further development for noninvasive breath alcohol screening.