Influencing Factors of Dissolved Organic Carbon Isotope Determination in Water Samples of a Karst Area by Wet Oxidation Method

Due to the high content of HCO3 − , low content of DOC and complex composition in the karst water, the current wet oxidation method for the determination of δ13CDOC needs to be improved. The study examined the impact of different pure waters, headspace bottle atmospheric equilibrium methods, DOC content, and the removal of bicarbonate (HCO3 − ) in water on δ13CDOC values. The experimental results show significant differences in the 44CO2 peak areas produced by different blank pure waters, with the most prominent peak area being 3.8 times the smallest. Using a gas-tight syringe for atmospheric equilibrium enhances the sample signal strength and ensures the optimal internal precision of the sample test results. Acidifying the water samples to pH<3 with phosphoric acid eliminates the influence of HCO3 − in karst waters. A nitrogen-blowing apparatus at a 250mL/min flow rate for 5−10min removes the free CO2 present after acidification. Under the above experimental conditions, the deviation between the test results and the calibrated reference values for karst water samples with DOC content greater than 2mg/L is better than 0.40‰ after blank correction. The difference in the measured results of δ13CDOC in karst water samples measured by the wet oxidation method compared to the total organic carbon analyzer-stable isotope mass spectrometer online method was less than 0.30‰. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202405130108.