Triple-isotope calibration of in-house water standards supplemented by determination of 17O content of USGS49-50 reference materials using cavity ring-down laser spectrometry
The procedure of calibrating in-house water standards suitable for routine analyses of triple-isotope composition of water samples using Picarro L2140-i CRDS analyser is presented and discussed. Such standards are indispensable for achieving and maintaining high quality of isotope analyses of water in terms of their precision and accuracy. A set of seven different water standards consisting of three in-house standards and four secondary standards commercially available was calibrated against VSMOW2/SLAP2 primary reference materials. The calibrated standards cover a wide range of isotopic composition, with δ values ranging from close to zero to the values comparable with SLAP2. The apparent consistency of the calibrated values of δ2H, δ18O and d-excess with corresponding certified values for commercially available USGS47-50 standards and the consistency of the calibrated values of δ17O and Δ17O with its literature values for USGS47-48 standards confirm the high quality of the performed calibration. Moreover, the calibration exercise allowed to obtain δ17O and Δ17O values for USGS49 and USGS50 standards, not reported so far.