Je. Baumgardner et Gr. Neufeld, COUNTERCURRENT EXTRACTION OF SPARINGLY SOLUBLE GASES FOR MEMBRANE INTRODUCTION MASS-SPECTROMETRY, Annals of biomedical engineering, 25(5), 1997, pp. 858-869
Membrane introduction mass spectrometry has been applied to inert gas
measurements in blood and tissue, but gases with low blood solubility
are associated with reduced sensitivity. Countercurrent extraction of
inert gases from a blood sample into a water carrier phase has the pot
ential to extract most of the gas sample while avoiding dependence of
signal on blood solubility. We present the design of a membrane counte
rcurrent exchange (CCE) device coupled with a conventional direct inse
rtion membrane probe to measure partial pressure of low solubility ine
rt gases in aqueous samples. A mathematical model of steady-state memb
rane CCE predicts that countercurrent extraction with appropriate sele
ction of carrier and sample flow rates can provide a mass spectrometer
signal nearly independent of variations in solubility over a specifie
d range, while retaining a linear response to changes in gas partial p
ressure over several orders of magnitude. Experimental data are presen
ted for sulfur hexafluoride and krypton in water samples. Optimal perf
ormance is dependent on adequate equilibration between the sample and
carrier streams, and the large resistance to diffusion in the aqueous
phase for insoluble gases presents a substantial challenge to the appl
ication of this principle.