Clumped Isotope Analysis of Calcite and Dolomite Mixtures Using Selective Acid Extraction

Acid extraction methods have been used in the last half century to selectively extract the CO 2 produced from different carbonate minerals in mixed samples. However, these methods are often time-consuming and labor intensive. Their application to clumped isotope (Δ 47 ) analysis has not been demonstrated. We propose here an acid extraction method with phosphoric acid for bulk stable and clumped isotope analysis that treats mixtures of calcite and dolomite the same regardless of the proportional composition. CO 2 evolved from calcite is extracted by allowing a reaction with phosphoric acid to proceed for 10 min at 50 °C. We then extract CO 2 evolved from dolomite by rapid ramping the acid temperature from 50 to 90 °C and allowing the reaction to complete. The experimental results show that our method yields accurate calcite and dolomite Δ 47 values from mixed samples under different proportional compositions. Our method also displays equal or higher accuracy for calcite δ 13 C and dolomite δ 13 C and δ 18 O values from mixtures when compared to previous studies. Our approach exhibits higher sample throughput than previous methods, is adequate for clumped isotopic analysis and simplifies the reaction progression from over 24 h to less than 2 h, while maintaining relatively high isotopic obtaining accuracy. It yet poorly resolves calcite δ 18 O values, as found with previous methods.