High-Precision Triple Oxygen Isotope Analysis of Carbon Dioxide by Tunable Infrared Laser Absorption Spectroscopy

Abstract

Precision measurements of the stable isotope ratios of oxygen (18O/16O and 17O/16O) in CO2 are critical to atmospheric monitoring and terrestrial climate research. High-precision 17O measurements by isotope ratio mass spectrometry (IRMS) are challenging because they require complicated sample preparation procedures, long measurement times, and relatively large samples sizes. Recently, tunable infrared laser direct absorption spectroscopy (TILDAS) has shown significant potential as an alternative technique for triple oxygen isotope analysis of CO2, although the ultimate level of reproducibility is unknown, partly because it is unclear how to relate TILDAS measurements to an internationally accepted isotope abundance scale (e.g., VSMOW2-SLAP2). Here, we present a method for high-precision triple oxygen isotope analysis of CO2 by TILDAS, requiring ∼8–9 μmol of CO2 (or 0.9 mg carbonate) in 50 min, plus ∼1.5 h for sample preparation and dilution of CO2 in N2 to a nominal 400 μmol mol–1. Overall reproducibility of Δ′17O (CO2) was 0.004‰ (4 per meg) for IAEA603 (SE, n = 6) and 10 per meg for NBS18 (SE, n = 4). Values corrected to the VSMOW2-SLAP2 scale are in good agreement with established techniques of high-precision IRMS, with the exception of Δ′17O measured by platinum-catalyzed exchange of CO2 with O2. Compared to high-precision IRMS, TILDAS offers the advantage of times less sample, and greater throughput, without loss of reproducibility. The flexibility of the technique should allow for many important applications to global biogeochemical monitoring and investigation of 17O anomalies in a range of geological materials.

A New Method for Silicon Triple Isotope Analysis With Application to Siliceous Sponge Spicules

“…In order to better use this proxy, more data with higher precision in Δ‘ 29 Si than presented here are required. Infrared absorption spectroscopic determination of Si isotopes on laser fluorination liberated SiF 4 may be an alternative to mass spectrometry and may provide data with improved precision (e.g., see Hare et al., 2022 or Perdue et al., 2022, for the case of triple O isotopes of CO 2 ).…”

A Dual Inlet System for Laser Spectroscopy of Triple Oxygen Isotopes in Carbonate‐Derived and Air CO2

“…Although the coolant temperature was in phase with the ambient room temperature, the cell temperature showed about 20 min lag because of the buffering effect of the hardware around the cell's temperature sensor (Figure 3b). Previous studies have also noted the detrimental effects of unstable cell and electronics hardware temperatures on the repeatability of the Δ′ 17 O measurements by laser spectroscopy (Bowling et al, 2003;Hare et al, 2022;Stoltmann et al, 2017).…”

“…(2022) and Hare et al. (2022), who used similar TILDAS systems. Our studies demonstrate that laser spectroscopy yields similar or better repeatability than more time‐intensive and expensive methods (Adnew et al., 2019; Fosu et al., 2020; Passey et al., 2014; Wostbrock, Cano, & Sharp, 2020).…”

“…Hare et al. (2022) and Perdue et al. (2022) further improved the inlet system and published 5–19 ppm external precision (±1 σ ) for Δ′ 17 O measurements of carbonates, thereby showing that laser spectroscopy can attain the precision required for biogeochemical applications.…”

Measurement of CO2 Isotopologue Ratios Using a Hollow Waveguide-Based Mid-Infrared Dispersion Spectrometer

“…However, commercial instruments typically do not support simultaneous multicomponent analysis, and a rather large sample volume (over 100 mL) is required. Compared to IRMS and NDIRS, LAS technology − has received increasing attention owing to its advantages such as high selectivity, fast response, small instrument size, simple operation, real-time online analysis, and the ability to determine multiple analytes simultaneously. In recent years, various techniques based on LAS for measuring carbon isotope ratios have been investigated, including off-axis integral cavity spectroscopy (OA-ICOS), cavity ring-down spectroscopy (CRDS), and wavelength modulation spectroscopy (WMS) .…”