Our Finnigan MAT 251 mass spectrometer is set up to measure the following light gas isotope ratios in pure gases using simultaneous collection of ionized species. In collaboration with Mike Bender at URI, we have developed a non-fractionating technique for extracting gases from seawater in order to precisely determine the ratios of O to N and Ar. This allows us to differentiate between biological and physical effects on the saturation level of oxygen.
Water is collected at sea into evacuated, pre-poisoned flasks.
The gas is equilibrated into the evacuated headspace in a temperature bath, the water is quickly removed and the extracted gas is returned to the laboratory. Back at SIL, the gas is transferred through liquid nitrogen traps to remove water and CO , then to a sample bottle at liquid helium temperature to quantitatively trap the gases.