Occurrence of triclosan (TCS) in water environment caused a serious concern due to TCS toxic properties as well as yield of toxic byproducts during natural attenuation. Here we developed an online approach for chlorine compound specific isotope analysis (CSIA) of TCS based on gas chromatography quadrupole mass spectrometry (GC-qMS). Specifically, the instrumental parameters including dwell time, ionization energy and split ratio values were tested and optimized. Moreover, the calculation scheme considering all the TCS molecular ions presented better precision compared with the method using the most abundant neighboring ion pairs. The optimized method was validated by applying it to differentiate various TCS manufacturers, and was used to resolve chlorine isotope fractionation occurring during TCS photodegradation induced by simulated solar radiation. Chlorine isotopic enrichment factor (${\epsilon }_{Cl}$) of −2.61 ± 0.37‰ and −0.72 ± 1.95‰ were obtained at pH values of 8.3 and 4.5, respectively. This indicates that preferential cleavage of C-Cl bonds occurred at a higher pH value. Thus, this study provides a robust and sensitive approach for chlorine CSIA of TCS, and could be readily applied to monitor chlorine isotope effects during TCS environmental transformations.

三氯生（TCS）在水环境中的存在引起了人们的严重关注，这是由于TCS的毒性以及自然衰减过程中有毒副产物的产生。在这里，我们开发了一种基于气相色谱四极杆质谱（GC-qMS）的TCS氯化合物特异性同位素分析（CSIA）在线方法。具体而言，对仪器参数（包括停留时间，电离能和分流比值）进行了测试和优化。此外，与使用最丰富的相邻离子对的方法相比，考虑所有TCS分子离子的计算方案具有更高的精度。通过将优化方法应用于不同的TCS制造商，对其进行了验证，并用于解决模拟太阳辐射引起的TCS光降解过程中发生的氯同位素分馏。氯同位素富集因子（${\epsilon }_{C升}$在pH值8.3和4.5时分别获得-2.61±0.37‰和-0.72±1.95‰）。这表明在较高的pH值下发生了C-Cl键的优先切割。因此，本研究为TCS的氯气CSIA提供了一种鲁棒且灵敏的方法，可以很容易地应用于监测TCS环境转变过程中的氯同位素效应。