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稳定碳同位素比值（^13C／^12C）是指示碳生物地球化学行为的有效指标。本研究研制并优化了CO2及其稳定同位素测定的吹扫预处理系统，将该系统与EA-IRMS联用实现了溶解CO2、其它形式DIC及二者碳同位素比值的在线同时测定，测得河口水样中易逃逸CO2及其它形式DIC的相对标准偏差分别为3．7％和3．0％；二者的δ^13C值的标准偏差分别为0．30％。和0．15‰。运用此法对九龙江9个站位表层水中不同形态DIC的碳同位素进行测定，得出易逃逸CO2的δ^13C平均值为-12．90‰，其他形式DIC的δ^13C平均值为-5．63‰。该法为水体中无机碳及其稳定碳同位素的测定研究提供了新途径。“,”Abstract:Stable carbon isotope ratios (^13C/^12C) are a useful tooi to trace the carbon biogeochemistry process. In this paper, a new on line pretreatment system coupling elemental analyzer connected with isotope ratio mass spectrometry (EA-IRMS) system was developed and the optimum running conditions for the pretreatment system were investigated. Using this system, dis- solved free CO2 (DFC), remainder DIC (non-DFC), δ^13CDFC and δ^13Cnon-DFC were determined simultaneously, with a standard de- viation of ±0.3‰ for δ^13CDFC and ±0.15‰ for δ^13non-DFC, and with a relative standard deviation of ±3.7‰ for DFC and ±3.0% for non-DFC. δ^13CDFC and δ^13Cnon-DFC of 9 samples collected from Jiulong River Estuary, China, were also measured, with a mean value of -12.90‰ for δ^13CDFC, and of-5.63‰ for δ^13 Cnon-DFC. This method would provide a new approach to study DIC and carbon isotopes in water.