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Measurements with sensor techniques in field analytical chemistry can be considerably affected by varying ambient conditions such as humidity. We systematically investigated the way in which ion mobility measurements are influenced by moisture. Both the peak positions of product ions within the spectrum and their relative abundance can vary depending on humidity. The transportation of humidity via the carrier gas into the ion mobility spectrometer causes changes in ionization pathways. Additional reactant ion species are formed and a lower relative abundance of product ions from halogenated compounds was generally observed. The peak position within the ion mobility spectrum is comparatively unaffected for the same ions. In contrast, considerable differences in drift times detected were found with increasing humidity of drift gas, while the influence on calibration was not as significant for chlorinated and brominated substances as observed for humid carrier gases.

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The ionization pathways were determined for sets of isomeric non-polar hydrocarbons (structural isomers, cis/trans isomers) using ion mobility spectrometry and mass spectrometry with different techniques of atmospheric pressure chemical ionization to assess the influence of structural features on ion formation. Depending on the structural features, different ions were observed using mass spectrometry. Unsaturated hydrocarbons formed mostlywere found for saturated cis/trans isomers using photoionization and 63 Ni ionization. These ionization methods and corona discharge ionization were used for ion mobility measurements of these compounds. Different ions were detected for compounds with different structural features. 63 Ni ionization and photoionization provide comparable ions for every set of isomers. The product ions formed can be clearly attributed to the structures identified. However, differences in relative abundance of product ions were found. Although corona discharge ionization permits the most sensitive detection of non-polar hydrocarbons, the spectra detected are complex and differ from those obtained with 63 Ni ionization and photoionization. (J Am Soc

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