Improved Apparatus for Phosphoric Acid Digestion of Carbonates to Determine the Carbon, Oxygen and Clumped Isotope Compositions

Abstract

The carbon, oxygen and clumped isotope compositions of carbonates are typically analyzed by carbonate-phosphoric acid digestion. Although this approach has been widely used since the 1950s, this procedure has problems in the operability. To address these issues, an improved apparatus with properly sized accessories, including an I-shaped vessel, a sample boat, a magnet, and a magnetic stir bar, has been developed for sample digestion. Similar to a long neck flask, this apparatus has a straight and axisymmetric structure, providing advantages in terms of cost and operability, and thus can be easily implemented in both open and sealed vessel digestion. To evaluate the reliability of the stable and clumped isotope compositions using this new vessel, international and interlaboratory carbonate standards were analyzed with this new apparatus and two commonly used Y-shaped and T-shaped vessels. The results using the new apparatus were consistent with those obtained by the others and in previous studies, suggesting suitability for the traditioinal phosphoric acid digestion of carbonates.