Analytical Method for Carbon and Oxygen Isotope of Small Carbonate Samples with the GasBench Ⅱ-IRMS Device

An analytical method for measuring carbon and oxygen isotopic compositions of trace amount carbonate (＞15 μg) was established by Delta V Advantage isotope Ratio MS coupled with GasBench Ⅱ. Different trace amount (5-50 μg) carbonate standard samples (IAEA-CO-1) were measured by GasBench Ⅱ with 12 mL and 3.7 mL vials. When the weight of samples was less than 40 μg and it was acidified in 12 mL vials, most standard deviations of the δ¹³C and δ¹⁸O were more than 0.1‰, which couldn’t satisfied high-precision measurements. When the weight of samples was greater than 15 μg and it was acidified in 3.7 mL vials, standard deviations for the δ¹³C and δ¹⁸O were 0.01‰-0.07‰ and 0.01‰-0.08‰ respectively, which satisfied high-precision measurements. Therefore, small 3.7 mL vials were used to increase the concentration of carbon dioxide in headspace, carbonate samples even less as 15 μg can be analyzed routinely by a GasBench Ⅱ continuous-flow IRMS. Meanwhile, the linear relationship between sample’s weight and peak’s area was strong (R²＞0.993 2) and it can be used to determine the carbon content of carbonate samples.