We can prepare gas for isotopic measurements from the following source materials:

Source Material	Source Isotopes Measured
Dissolved Gasses O and N			O	N
Dissolved Inorganic Carbon	C	C
Particulate Organic Carbon and Nitrogen	C	C		N
Atmospheric CO, H, CO and CH	C	C	O		DH
Water			O		DH
Nitrate				N

Instrumental Capabilities:

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.

gas isotope reproducibility(per mil)

Molecule	Isotope	per mil	Isotope	per mil
CO	C	± 0.015	O	± 0.020
N	N	± 0.015
O	O	± 0.020	O	± 0.10
H	H	± 0.15

In addition, by mass jumping between peaks, we can measure gas ratios and isotope ratios in mixtures of gases to a high precision:

gas ratio reproducibility(per mil)

O/Ar ± 0.3
O/N ± 0.5
N/Ar ± 0.5

isotope ratio in mixture reproducibility(per mil)

N ± 0.08
O ± 0.20
O ± 0.08

Gas Ratio Measurement:

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.