Use of humidified air in optimizing APCI-MS response in breath analysis.
An atmospheric-pressure chemical ionization-mass spectrometer (APCI-MS) system was modified to introduce gaseous samples as well as to humidify sheath and auxiliary gases. Solutions of single odorants in pentane were evaporated inside a vessel in a dry environment (relative humidity 0-10%) and in a human-breath-like environment (relative humidity 88-98%) and subsequently analyzed in the positive ion mode. The results indicated that using dry nitrogen as sheath and auxiliary gases led to strong fragmentation of the molecules combined with a low sensitivity of detection. Humidification of both gases not only increased sensitivity but also resulted in the protonated molecular ion as the base peak in 5 of the 6 compounds studied (ethyl butyrate, 3-methyl-3-phenyl glycidic acid ethyl ester, gamma-decalactone, (E)-2-hexenal, and cinnamic aldehyde). Only hexanal, which formed a cluster (m/z 183), did not have the protonated molecular ion as base peak. It was found that the humidity of the sample itself did not have any influence on sensitivity or fragmentation.
Zehentbauer
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Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Avenue, St. Paul, Minnesota 55108, USA.
Krick
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Reineccius
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GA
D000388:Air; D001944:Breath Tests / Q000295:instrumentation / Q000379:methods; D006801:Humans; D006813:Humidity; D013058:Mass Spectrometry / Q000379:methods; D009812:Odorants / Q000032:analysis*; D012119:Respiration