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

Abstract Analyzing the triple oxygen isotope (Δ′ 17 O) composition of carbonates and air CO 2 can provide valuable information about Earth system processes. However, accurately measuring the abundance of the rare 17 O‐bearing CO 2 isotopologue using isotope ratio mass spectrometry presents significant challenges. Consequently, alternative approaches, such as laser spectroscopy, have been developed. Here, we describe an adaptable dual inlet system for a tunable infrared laser direct absorption spectrometer (TILDAS) that maintains stable instrumental conditions for subsequent sample and reference measurements. We report ∆′ 17 O measurements on three types of samples: reference CO 2 , CO 2 derived from the acid digestion of carbonates, and air CO 2 . The external repeatability (±1 σ ) for reference‐sample‐reference bracketing measurements is generally better than ±10 ppm, close to the average internal error of ±6 ppm. Our results demonstrate that laser spectroscopy is a capable technique for measuring triple oxygen isotopes with the precision required to resolve variations in the ∆′ 17 O values of air CO 2 and to use the ∆′ 17 O of carbonates for paleothermometry.