Quantitation of dissolved gas content in emulsions and in blood using mass spectrometric detection

Abstract

Quantitation of dissolved gases in blood or in other biological media is essential for understanding the dynamics of metabolic processes. Current detection techniques, while enabling rapid and convenient assessment of dissolved gases, provide only direct information on the partial pressure of gases dissolved in the aqueous fraction of the fluid. The more relevant quantity known as gas content, which refers to the total amount of the gas in all fractions of the sample, can be inferred from those partial pressures, but only indirectly through mathematical modeling. Here we describe a simple mass spectrometric technique for rapid and direct quantitation of gas content for a wide range of gases. The technique is based on a mass spectrometer detector that continuously monitors gases that are rapidly extracted from samples injected into a purge vessel. The accuracy and sample processing speed of the system is demonstrated with experiments that reproduce within minutes literature values for the solubility of various gases in water. The capability of the technique is further demonstrated through accurate determination of O(2) content in a lipid emulsion and in whole blood, using as little as 20 μL of sample. The approach to gas content quantitation described here should greatly expand the range of animals and conditions that may be used in studies of metabolic gas exchange, and facilitate the development of artificial oxygen carriers and resuscitation fluids.

Figure 1

General approach to the measurement of gas content from complex fluids. A) A complex fluid may consist of an aqueous liquid containing different types of particles such as miscelles or cells, all with varying gas affinities. When in equilibrium, gas molecules enter and leave each type of particle at an identical rate. B) When a sample of the fluid is injected into an aqueous solution purged with an inert gas, the bubbling action captures and removes the dissolved gas from the water partition. Unable to uptake new gas molecules, the particles begin to discharge their gas content. C) Eventually all gas content from the particles and the water partition is completely dissipated into the headspace.

Figure 2

Schematic of the apparatus developed for rapid extraction of dissolved gases and for their quantitation using mass spectrometry.

Figure 3

Representative mass chromatogram for m/z = 32 and 44, corresponding to the molecular masses of oxygen and carbon dioxide, respectively. The signals were obtained from 100 μL of water exposed to atmospheric gas at STP.

Figure 4

Representative chromatograms that quantify oxygen (m/z=32) content from (A) a 20% olive oil emulsion and (B) from mouse blood. For consistency, all samples including water were incubated for an hour with 100% oxygen prior to injection.