High-Precision Simultaneous ¹⁸O/¹⁶O, ¹³C/¹²C, and ¹⁷O/¹⁶O Analyses for Microgram Quantities of CaCO₃ by Tunable Infrared Laser Absorption Spectroscopy

Abstract

Stable isotope ratios (18O/16O, 13C/12C, and 17O/16O) in carbonates have contributed greatly to the understanding of Earth and planetary systems, climates, and history. The current method for measuring isotopologues of CO2 derived from CaCO3 is primarily gas-source isotope ratio mass spectroscopy (IRMS). However, IRMS has drawbacks, such as mass overlap by multiple CO2 isotopologues and contaminants, the requirement of careful sample purification, and the use of major instrumentation needing permanent installation and a high power electrical supply. Here, we report simultaneous 18O/16O, 13C/12C, and 17O/16O analyses for microgram quantities of CaCO3 using a tunable mid-infrared laser absorption spectroscopy (TILDAS) system, which has no mass overlap problem and yields high sensitivity/precision measurements on small samples, as small as 0.02 μmol of CO2 (equivalent to 2 μg of CaCO3) with standard errors of less than 0.08 ‰ for 18O/16O and 13C/12C (±0.136 ‰ and ±0.387 ‰ repeatability; n = 10). In larger samples of CO2, 0.68 μmol (or 68 μg of CaCO3), standard error is less than 0.04 ‰ for 18O/16O and 13C/12C (< ±0.1 ‰ repeatability; n = 10) and 0.03 ‰ for 17O/16O (±0.069 ‰ repeatability; n = 10). We also show, for the first time, the relationship between 17O/16O ratios measured using the TILDAS system and published δ17O values of international standard materials (NBS-18 and −19) measured by IRMS. The benchtop TILDAS system, with cryogen-free sample preparation vacuum lines for microgram quantities of carbonates, is therefore a significant advance in carbonate stable isotope ratio geochemistry and is a new alternative to conventional IRMS.

Laser Absorption Spectroscopy of Rare and Doubly Substituted Carbon Dioxide Isotopologues

“…12 C 16 O 17 O isotopologue and, therefore, δ 17 O, this was demonstrated earlier by Stoltmann et al41 and Sakai et al42 . Mass spectrometric analysis of CO 2 isotopologues with substituted 17 O are only possible if the isobaric interference with more abundant 13 C substituted isotopologue of CO 2 can be resolved or if a different technique is used (e.g., reduction and fluorination 43 ).…”

Evaluation of a field-deployable Nafion™-based air-drying system for collecting whole air samples and its application to stable isotope measurements of CO&lt;sub&gt;2&lt;/sub&gt;

“…At the CIO we employed a dual-laser tunable infrared laser direct absorption spectrometer (TILDAS, Aerodyne Research, Inc.) (McManus et al, 2015;Sakai et al, 2017), which we refer to as the TILDAS-SICAS (SICAS for stable isotopes of CO 2 measurements in atmospheric samples), for the measurements of 16 O 13 C 16 O, 16 O 12 C 17 O and 16 O 12 C 18 O in whole air samples. More details about the TILDAS-SICAS setup and performance will be described elsewhere in a forthcoming paper.…”

“…The drying capacity and endurance of the Nafion™ tubes in combination with the molecular sieve drier cartridge were examined under laboratory test conditions with sample air containing ∼ 4 % H 2 O at 33 • C, resembling extreme tropical conditions. Isotopic measurements of sample air fed through the NAD were performed using the dual-laser tunable infrared laser direct absorption spectrometer (TILDAS, Aerodyne Research, Inc.) at Groningen, specially designed for the measurements of all the three singly substituted CO 2 isotopologues, 16 O 13 C 16 O, 16 O 12 C 17 O and 16 O 12 C 18 O, in whole air samples (McManus et al, 2015;Sakai et al, 2017). Finally, we present the results of a series of performance tests of the NAD in combination with a PCP and PFP sampling system simulating field conditions.…”

Taking the Temperature of Hydrothermal Ore Deposits Using Clumped Isotope Thermometry

“…Using the LIDI method, aliquots of ~100 μg of carbonate are measured in 45 minute cycles (Müller et al, 2017). Issues associated with partial reset of clumped isotope temperatures, due to equilibration with water during sample preparation, can be overcome by implementing advanced cryogen-free techniques for purification of CO2 (e.g., Sakai et al, 2017). Recently developed infrared absorption spectrometers also provide an alternative platform for clumped isotope analyses (Nelson, 2016;Sakai et al, 2017).…”

“…Issues associated with partial reset of clumped isotope temperatures, due to equilibration with water during sample preparation, can be overcome by implementing advanced cryogen-free techniques for purification of CO2 (e.g., Sakai et al, 2017). Recently developed infrared absorption spectrometers also provide an alternative platform for clumped isotope analyses (Nelson, 2016;Sakai et al, 2017). In addition to lower hardware cost, laser instruments may eliminate issues associated with contamination imparted by sulfur, hydrocarbon, and chlorocarbon compounds, which frequently occur in hydrothermal carbonates, and interfere with measurement of 47 CO2.…”