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On‐line measurement of the absolute humidity of air, breath and liquid headspace samples by selected ion flow tube mass spectrometry
Author(s) -
S̆panĕl Patrik,
Smith David
Publication year - 2001
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.265
Subject(s) - chemistry , mass spectrometry , analytical chemistry (journal) , tube (container) , chromatography , ion , line (geometry) , humidity , meteorology , organic chemistry , geometry , mathematics , mechanical engineering , physics , engineering
We describe how selected ion flow tube mass spectrometry (SIFT‐MS) can be used to determine the absolute humidity of air, breath and liquid headspace samples. This involves the determination of the relative count rates of the H 3 O + ions and those H 3 O + .(H 2 O) 1,2,3 hydrate ions that inevitably form in the helium carrier gas when humid samples are being analysed by SIFT‐MS using H 3 O + precursor ions. This requires an understanding of the kinetics of hydrated hydronium ion formation, the involvement of mass discrimination in the analytical quadrupole mass spectrometer and the decreased diffusive loss of the heavier hydrates along the flow tube. Thus, we show that the humidity of breath and liquid headspace samples, typically at the few percent level, can be directly obtained on‐line to the SIFT‐MS instrument along with the concentrations of trace gases, which are present at much lower levels. We emphasise the value of parallel humidity measurements in ensuring good real‐time sampling of breath and liquid headspace and the value of such measurements to trace gas analysis using SIFT‐MS. Copyright © 2001 John Wiley & Sons, Ltd.