On the reproducibility and repeatability of laser absorption spectroscopy measurements for δ2H and δ18O isotopic analysis

The aim of this study was to analyse the repro- ducibility of off-axis integrated cavity output spectroscopy (OA-ICOS)-derived 2 H and 18 O measurements on a set of 35 water samples by comparing the performance of four laser spectroscopes with the performance of a conventional mass spectrometer under typical laboratory conditions. All samples were analysed using three different schemes of stan- dard/sample combinations and related data processing to as- sess the improvement of results compared with mass spec- trometry. The repeatability of the four OA-ICOS instruments was further investigated by multiple analyses of a sample subset to evaluate the stability of 2 H and 18 O measure- ments. Results demonstrated an overall agreement between OA- ICOS-based and mass spectrometry-based measurements for the entire dataset. However, a certain degree of variability existed in precision and accuracy between the four instru- ments. There was no evident bias or systematic deviations from the mass spectrometer values, but random errors, which were apparently not related to external factors, significantly affected the final results. Our investigation revealed that ana- lytical precision ranged ±from ±0.56‰ to ±1.80‰ for 2 H and from ±0.10‰ to ±0.27‰ for 18 O measurements, with a marked variability among the four instruments. The over- all capability of laser instruments to reproduce stable results with repeated measurements of the same sample was accept- able, and there were general differences within the range of the analytical precision for each spectroscope. Hence, av- eraging the measurements of three identical samples led to a higher degree of accuracy and eliminated the potential for random deviations.