Improving memory effect correction to achieve high precision analysis of δ 17 O, δ 18 O δ 2 H, 17 O‐excess and d‐excess in water using cavity ring‐down laser spectroscopy

Christine Vallet-Coulomb (1) , Martine Couapel (1) , Corinne Sonzogni (1)

1 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

Rationale The precision obtained in routine isotope analysis of water (δ17O, δ18O, δ2H, 17O‐excess and d‐excess values) by Cavity Ring‐Down Spectroscopy is usually below the instrument specifications provided by the manufacturer. This study aimed at reducing this discrepancy, with particular attention paid to mitigating the memory effect (ME). Methods We used a Picarro L2140i analyzer coupled with a high‐precision A0211 vaporizer and an A0325 autosampler. The magnitude and duration of the ME were estimated using 24 series of 50 successive injections of samples with contrasting compositions. Four memory correction methods were compared, and the instrument performance was evaluated over a 17‐month period of routine analysis, using two different run architectures. Results The ME remains detectable after the 30th injection, implying that common corrections procedures only based on the last preceding sample need to be revised. We developed a new ME correction based on the composition of several successive samples, and designed a run architecture to minimize the magnitude of the ME. The standard deviation obtained from routine measurement of a QA water over a 7 months‐period was 0.015‰ for δ17O, 0.023‰ for δ18O, 0.078‰ for δ2H, 0.006‰ for 17O‐excess and 0.173‰ for d‐excess. In addition, we provided the first δ17O and 17O‐excess values for the GRESP certified reference material. Conclusions This study demonstrates the long‐term persistence of the ME, which is often overlooked in routine analysis of natural samples. As already evidenced when measuring labelled water, it calls for consideration of the compositions of several previous samples to obtain an appropriate correction, a prerequisite to achieve high precision data.

Domaines: Sciences de la Terre

Christine Vallet-Coulomb, Martine Couapel, Corinne Sonzogni. Improving memory effect correction to achieve high precision analysis of δ 17 O, δ 18 O δ 2 H, 17 O‐excess and d‐excess in water using cavity ring‐down laser spectroscopy. Rapid Communications in Mass Spectrometry, 2021, ⟨10.1002/rcm.9108⟩. ⟨hal-03209687⟩