Reference Materials: We are tied to the VSMOW international scale via internal laboratory reference waters measured against VSMOW and SLAP for our water isotope measurements.
Sample Submission: If you would like to submit water samples for δD analysis, we prefer a minimum of 5 mL of frozen sample in a labeled water tight plastic container that is large enough and strong enough to withstand water expansion upon freezing. Simple legible sample IDs are appreciated. We need to know if it is fresh or salt water. Please include in your shipment container the following form (pdf or doc) and email Andy.
Exhaustive description of analysis: The chromium reduction of water to H2 gas is facilitated with a 2 µL injection of water into an evacuated 850 °C chromium containing quartz reactor all contained in an Finnigan HDevice. After reaction / equilibration (60 seconds), H2 is expanded into a variable volume bellow. Mass / charge 2 and 3 of this sample H2 gas are measured alternately with a reference H2 gas, roughly calibrated to the VSMOW scale, in a Finnigan Delta Plus dual-inlet isotope ratio mass spectrometer. Samples are interspersed with internal laboratory reference waters calibrated against VSMOW (δD = 0 ‰) and SLAP (δD = -428 ‰), using GISP (δD = -190 ‰) as a quality control reference. Individual samples and standards are injected 3 times each to account for known memory effects. The 10 µL syringe is rinsed with each sample / standard prior to formal injection and rinsed with deionized water after each injection.
Calculations: The IsoDat software provided δD values relative to the reference gas (along with all other selected data) are imported into a matlab script for data reduction. The memory effect is typically 95% (i.e. 95% of the current measurement is from the present injection) and is therefore dealt with by excluding the first injection of a vial. The subsequent two injections are averaged to obtain vial level data. A linear regression is completed using the raw vial δD values for two of our internal reference waters and the accepted values. All data are corrected to VSMOW using this linear equation. Precision and accuracy are estimated for each run using a third internal reference water that is treated as an unknown. Reference waters are chosen to flank the sample range in δD values. All reference water δD values can be seen here.