湿氧化法测定岩溶区水体中溶解有机碳同位素的影响因素研究  

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

作　　者：杨会[1,2] 吴夏 俞建国[1,2] 唐伟 蓝高勇[1,2] YANG Hui;WU Xia;YU Jianguo;TANG Wei;LAN Gaoyong(Institute of Karst Geology,Chinese Academy of Geological Sciences,Key Laboratory of Karst Dynamics,Ministry of National Resources&Guangxi Autonomous,Region/International Research Center on Karst under the Auspices of UNESCO,Guilin 541004,China;Pingguo Guangxi,Karst Ecosystem,National Observation and Research Station,Pingguo,Guangxi 531406,China)

机构地区：[1]中国地质科学院岩溶地质研究所,自然资源部/广西岩溶动力学重点实验室/联合国教科文组织国际岩溶研究中心,广西桂林541004 [2]广西平果喀斯特生态系统国家野外科学观测研究站,广西平果531406

出　　处：《岩矿测试》2024年第6期914-927,共14页Rock and Mineral Analysis

基　　金：国家自然科学基金项目(41501222);广西自然科学基金项目(2018GXNSFBA138042,2018GXNSFAA281320);中国地质科学院岩溶地质研究所基本科研业务费项目(2023015,2023018);浙江省地质碳汇调查、监测与应用试点项目(浙地质函[2024]35号)。

摘　　要：溶解有机碳(DOC)是研究岩溶作用强度、岩溶碳源、汇特征与岩溶碳循环过程的重要指标。利用岩溶区DOC碳同位素值(δ^(13)CDOC),可以精确计算岩溶流域的碳源和汇通量,这一参数对于全球气候变化研-究至关重要。鉴于岩溶区水体中HCO_(3)^(−)含量较高,DOC含量较低且组分复杂,目前湿氧化法应用于测定岩溶区域水体中δ^(13)CDOC值的检测方法尚未完善。本文采用GasBenchⅡ与同位素比质谱分析(IRMS)联用技术,探讨了湿氧化法测试岩溶水体中δ^(13)CDOC值的影响因素。针对不同市售纯水、顶空瓶与大气的平衡方式、DOC-含量、水中碳酸氢根(HCO3)去除,研究了这些因素对44CO_(2)峰面积和δ^(13)CDOC测量的影响。实验结果表明:不同空白纯水产生的44CO_(2)峰面积存在显著差异,最大44CO_(2)峰面积是最小44CO_(2)峰面积的3.8倍。采用气密针与大气平衡的方式能增强样品信号强度,同时确保样品测试结果的内精度最优。水样用磷酸酸化至pH<3-时,可以消除岩溶水体中HCO_(3)^(−)的影响。使用氮吹仪在250mL/min流速下吹扫5~10min,可以去除酸化后可能存在的游离CO_(2)。在使用无菌双蒸水作为空白,气密针与大气平衡,磷酸酸化至pH<3,250mL/min流速吹扫5min的实验条件下,对于DOC含量大于2mg/L的岩溶区水样,经过空白校正,可以确保测试结果与标定参考值的偏差优于0.40‰。湿氧化法测定岩溶区水样中δ^(13)CDOC的结果与总有机碳分析-仪-稳定同位素质谱仪联机方法进行对比,测定结果差值小于0.30‰。利用湿氧化法测试岩溶区高HCO3含量的δ^(13)CDOC样品能够满足测试要求。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 ofδ^(13)CDOC 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(HCO_(3)^(−))in water onδ^(13)CDOC values.The experimental results show significant differences in the 44CO_(2) 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 HCO_(3)^(−)in karst waters.A nitrogen-blowing apparatus at a 250mL/min flow rate for 5−10min removes the free CO_(2) 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 ofδ^(13)CDOC 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‰.

关 键 词：溶解有机碳 碳酸氢根 湿氧化法 同位素质谱法 空白样品 

分 类 号：O657.63[理学—分析化学]