Membrane introduction mass spectrometry of nonpolar hydrocarbons using nitric oxide chemical ionization

Selectivity enhancement of membrane introduction mass spectrometry of nonpolar alkanes, alkenes, and aromatic hydrocarbons in air samples by application of nitric oxide chemical ionization (NOCI/MIMS) is demonstrated. Membrane methods are useful for separating compounds (usually nonpolar organics) from air and water samples without costly and time-consuming sample preparation, and coupled with mass spectrometry, they provide good sensitivity. But they often suffer from lack of specificity in mixture analysis, particularly for saturated organics. Nitric oxide chemical ionization is able to produce strong unique ion signals for many hydrocarbon test compounds that can be used to identify and quantify the parent neutrals. Our observed detection limits for a number of test compounds were relatively high; however, the method could potentially be useful for environmental analytical applications (e.g., plume tracking) if the monitored compound was at elevated levels or if NOCI/MIMS is coupled with a trapping method.