Water Isotope Analysis Techniques
Oxygen and deuterium of water analysis techniques
This headspace technique is used primarily for waters with greater than 4PSU (salinity), and for waters and other liquids that contain hydrocarbons or alcohol.
Either plastic or glass bottles can be used for sampling water for O & D, as long as the bottles are air-tight and have a minimum of headspace. Water for this type of analysis can be kept at room temperature for years. We require a minimum of 2mL of water.
When filling out the submission form, you MUST indicate the salinity and the pH of the samples. This information is critical for us to be able to choose the correct method of preparation for analysis; for example, saline waters must be left to equilibrate much longer after being flushed and filled with the gas mixture than fresh water samples.
Deuterium-hydrogen isotopes in water are determined on a Finnigan MAT Delta plus XP + Gasbench. Platinum catalyst pellets are added to Exetainer vials containing 0.2 mL (fresh) or 0.6mL (saline) of water. The vials are flushed and filled with a gas mixture of 2% hydrogen in helium off-line using a set-up designed by Paul (see photo). The H2 gas is analysed automatically in continuous flow. The results are normalized to VSMOW. The routine precision (2 sigma) of the analysis is +/-2.0 permil.
The oxygen isotopic composition of water is determined in a similar manner by CO2-water equilibration using 0.2 mL (fresh) or 0.6mL (saline) of water without the catalyst pellets, and a gas mixture of 2% CO2 in helium. The CO2 is analysed on the same Finnigan MAT Delta plus XP + Gasbench. The routine precision (2 sigma) of the analyses is +/-0.15 permil.
Both isotopes can be determined from a single aliquot of water. In this case, it is preferrable to run the oxygen first, then run the hydrogen with the platinum catalyst pellets.
LGR - TWVIA
Fresh waters with less than 4PSU can be analysed using the Los Gatos Research (LGR) Triple Water Vapour Isotope Analyzer. This unit can determine the H/D, 18O and 17O data from a single injection of 0.75uL of water; multiple injections are averaged for better precision.
Ideally we would like 1.0mL of 0.4um filtered water in a 2mL glass GC vial (either crimp or screw cap). The website price includes filtering and pipetting into the correct vials if the researcher prefers to send a small bottle of water as described in the Gasbench section.