We are using the equilibration method H2/CO2 - water with GasBech (CF-IRMS) for d18O and d2H in water. USGS LIMS is used for drift correction, normalization and data management.
We observed that the sample condenses in the septum, which can increase the carry of water to the GasBench. The temperature of GasBench is 28 oC and the room temperature 24 oC. We are working with the minimum of 18 hours equilibration.The background m/z=18 is increasing to high values, until 15000 mV after the run. Usually we are carrying the baking of the GC Column (120 oC) ,as suggested by paper of Rangarajan and Ghosh (2011), after the batch of samples. We are monitoring the background of m/z=18 before and after the run for d18O.
We appreciate all comments about this issue.
Rangarajan R. and Ghosh, P.; Role of water contamination within the GC column of a GasBench II peripheral on the reproducibility of 18O/16O ratios in water samples. Isotopes in Environmental and Health Studies, v. 47, n. 4, 498-511, 2011.