Solubility of helium, argon, and sulfur hexafluoride in human blood measured by mass spectrometry.

A method has been developed to measure the solubility coefficients of gases in liquids by respiratory mass spectrometry. A sample (2.5 ml) pf the test liquid, equilibrated with a test gas mixture, is injected into a sealed flask (approximately 140 ml) for extraction by equilibration. The reequilibrated gas phase in the flask is analyzed by a mass spectrometer. Separately, an equal volume (2.5 ml) of the equilibrating test gas mixture is injected into a larger sealed flask (approximately ll liter) where it is mixed and then analyzed by the mass spectrometer. Solubility in the liquid is calculated from the ratio of mass spectrometer readings in both flasks and the ratio of flask volumes. The ratio of volumes of the small and the large flasks is made similar to the gas/liquid partition coefficient whereby the mass spectrometer readings in both become similar. With this approach, errors due to amplifier and mass spectrometer nonlinearity are greatly attenuated. The method was used to measure the solubility of helium, argon, and sulfur hexafluoride in distilled water, human plasma, and human blood.