A Comparison of Moisture Removing Strategies for Breath Samples Spiked with Trace Concentrations of Hydrogen Sulphide

Hydrogen sulphide (H2S) was traditionally recognized as a pungent toxic gas, but this view has now been revised to include its role as an endogenously produced signaling molecule in mammalian cells, affecting various physiological and pathophysiological processes. Endogenously produced H2S in tissues and blood is reported to be lower than 15 nmol/L [1], which requires sample pre-concentration step and sensitive detection technologies. Gas chromatography (GC) equipped with a variety of detectors is regarded of the choice for quantitative detection of H2S. However, the high background moisture in mammalian breath greatly challenges the selectivity and sensitivity of this technique and dictates the need for interfacing moisture trapping techniques prior to preconcentration and detection steps. In preparation for exhaled breath-H2S analysis by the combined use of moisture trapping, cryogenic pre-concentration, thermal desorption and GC technique, we quantitatively evaluated the moisture removing and H2S permeating efficiency of CaCl2, silica gel, molecular Sieve 4A, a membrane type dryer, and sample cooling (in the range of 45oC to -20oC) using Selected Ion Flow Tube – Mass Spectrometry (SIFT-MS) as a simultaneous means of detecting H2O and H2S in human breath samples spiked with H2S and humidified with distilled water. While CaCl2, membrane type dryer, and sample freezing remove moisture to as low as 0.4% without affecting H2S, silica gel and molecular Sieve 4A removed both moisture and H2S in the studied samples. Cartridges containing 0.4 g – 1.6 g CaCl2 as desiccant appear to be a viable alternative to more expensive membrane dryers.