The discovery of a new ionization technology can greatly promote the application of mass spectrometry in certain field. Recent researches found a new phenomenon: Ionization efficiencies of oxygenated hydrocarbons can be enhanced two or three magnitudes via CH2Cl2 doping in VUV photoionization. This phenomenon is essentially an excited-state CH2Cl2 induced chemi-ionization reaction, which was developed into a unique ionization technique. Currently, the chemi-ionization technique coupled with time-of-flight mass spectrometry has been applied in the real-time detection for lung cancer biomarkers, policy-sensitive amines, and taste and odor (T&O) compounds. The experimental studies on lung cancer biomarkers showed that the signal intensities of n-propanol, n-pentanal, acetone, and butyl acetate increased significantly after injecting CH2Cl2. Meanwhile the VOCs concentrations and the corresponding signal intensities exhibited good linearity. For organic amines, the signal intensities of aniline, benzylamine, phenethylamine, amphetamine, and their structural isomers were amplified by 60-130 times after doping 9×103 ppmv CH2Cl2. Under the 10 s detection time, the LODs of aniline and benzylamine were 36 and 22 pptv, respectively. Via headspace sampling, the calibrated LODs of T&O compounds (2-methylbutyraldehyde, methyl tert-butyl ether, methyl methacrylate, 2-isobutyl-3-methyoxypyrazine, and 2-isopropyl-3-methoxypyrazine) in water were calculated to be 3.5-50.2 ng L-1, and the estimated LODs of 2-methylisoborneol and geosmin were 0.25 and 0.77 ng L-1, respectively. The instrumental LODs of earthy-musty odors are comparable to those obtained using liquid-liquid micro-extraction coupled or headspace solid-phase extraction coupled with GC, and are superior to human odor thresholds. These experimental results reveal that, the chemi-ionization TOF-MS is a promising on-line detection technique with great potential for disease screening, social security, and environmental monitoring.

Application of novel excited-state CH2Cl2-induced chemi-ionization coupled with time-of-flight mass spectrometry for the real-time detection of volatile organics

2019 Spring National Meeting

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