气相色谱-负化学源质谱法测定船舶压载水中4种三卤甲烷北大核心CSCD

我国每年的船舶压载水排放量巨大,压载水中含有浮游生物、病原体及其幼虫或孢子等,若处理不当,会对排放水域的生态环境造成严重影响。排放压载水前常使用电解法对其进行处理,电解产生的次氯酸钠溶液,能有效杀灭残余的微生物。但电解后会产生副产物三卤甲烷(THMs),其对人体有一定的健康风险,建立船舶压载水中三卤甲烷的测定方法具有重要意义。该研究建立了采用气相色谱-负化学源质谱(GC-NCI-MS)测定船舶压载水中4种三卤甲烷(包括三氯甲烷、二氯一溴甲烷、一氯二溴甲烷、三溴甲烷)的分析方法。船舶压载水样品经过顶空进样技术处理后,通过DB-5MS UI毛细管色谱柱(30 m×0.25 mm×1.0μm)分离,气相色谱-负化学源质谱仪测定,在选择离子扫描(SIM)模式下分析,采用外标法进行定量。4种三卤甲烷在0.2~50μg/L范围内线性关系良好,相关系数(r)≥0.995,定量限(S/N=10)为0.1~0.2μg/L,在0.2、0.5、2.0μg/L 3个加标水平下,4种THMs的平均回收率为90.3%~106.8%,相对标准偏差(RSD)为1.4%~6.2%。该方法准确、稳定、可靠,可用于测定船舶压载水中4种THMs的含量。使用建立的测定方法对36个船舶压载水进行测定,三溴甲烷、二溴一氯甲烷、一溴二氯甲烷与三氯甲烷的检出率分别为83.3%、69.4%、22.2%和19.4%,检出值分别为34.25~221.5μg/L、3.52~41.87μg/L、1.52~8.56μg/L和0.02~5.46μg/L。

Determination of four trihalomethanes in ship ballast water by gas chromatography-negative chemical ionization-mass spectrometry

Ship ballast water can control the roll, trim, and draft of the ship, and thus ensuring the balance and stability of the ship in the course of sailing, and playing a vital role in the safe navigation of ships. The annual discharge of ship ballast water is very large in China. About three to five billion cubic meters of ship ballast water is discharged into offshore or inland waters every year. This water contains plankton, pathogens, and their larvae or spores. If not be handled appropriately, this will have a serious impact on the ecological environment of the discharge waters. Ballast water is usually treated by electrolysis before being discharged. Sodium hypochlorite can be generated, which can kill microorganisms; however, the by-products trihalomethanes (THMs) are cytotoxic and biotoxic. Studies have shown that THMs may cause fetal growth retardation, spontaneous abortion, or death. The concentration of THMs in drinking water is closely related to the risk of bladder cancer death. Hence, it is important to establish a method for the determination of THMs in ship ballast water. The four kinds of THMs are chloroform, dichlorobromomethane, chlorodibromomethane, and tribromomethane. At present, ship ballast water is mostly analyzed by gas chromatography (GC) using an electron capture detector (ECD) or by gas chromatography-mass spectrometry (GC-MS). Given the low boiling point of THMs, headspace injection and purge-and-trap can be used. Gas chromatography-negative chemical ionization-mass spectrometry (GC-NCI-MS), was adopted. NCI is a soft ionization technique that shows special response to compounds bearing electronegative elements or groups. THMs contain electronegative chlorine atoms and bromine atoms. Therefore, NCI is a good choice for their analysis. The samples were processed by the headspace injection technique. The NaCl content in 10 mL sample was optimized in headspace injection. The results showed that 3.0 g NaCl was the most suitable dosage. The analytes were separated on a DB-5MS UI capillary-column (30 m×0.25 mm×1.0 μm). The target compounds were quantified by using the external standard method in selected ion monitoring (SIM) mode. The four THMs were not only well separated but also showed a high response at 0.2 μg/L. The four THMs showed good linear relationships in the range of 0.2-50 μg/L, with correlation coefficients≥0.995. The limits of quantification (LOQs, S/N=10) were 0.1-0.2 μg/L, and the average recoveries of the four THMs were 90.3%-106.8% at the three spike levels of 0.2, 0.5, and 2.0 μg/L. The relative standard deviations were 1.4%-6.2%. The LOQs of the THMs in the GB/T 5750.8-2006 Standard Test Method of Drinking Water Organic Matter Index are 0.3-6.0 μg/L. It can be seen that the LOQs of the THMs are greatly reduced in this study. The proposed method is accurate, stable, and reliable, and it can be used for monitoring the four THMs in ship ballast water. The method was applied for the detection of 36 ship ballast water samples. In all cases, the detection rates of tribromomethane, chlorodibromomethane, dichlorobromomethane, and chloroform were 83.3%, 69.4%, 22.2%, and 19.4%, respectively. The detection values of tribromomethane, chlorodibromomethane, dichlorobromomethane, and chloroform were 34.25-221.5 μg/L, 3.52-41.87 μg/L, 1.52-8.56 μg/L, and 0.02-5.46 μg/L, respectively. Based on the analysis of several ship ballast water samples (electrolytic water), it was concluded that the greater the number of bromine atoms in the THMs, the higher are the detection rate and detection value in ship ballast water. Compared to chloroform, tribromomethane is more harmful to living beings. China has acceded to the International Convention on Ship Ballast Water and Sediment Control and Management. There is an urgent need to establish analysis methods with high sensitivity, good stability, and high accuracy in addition to determining standards and regulations for ship ballast water.