DP-PT-GC-CVAFS法分析水中烷基汞的影响因素和方法适用性

摘要

Alkylmercury,including methylmercury (MeHg) and ethylmercury (EtHg),are important chemicals issued in the discharge standard for industrial and domestic wastewater and the quality standard for surface water in China.However,the analysis of alkylmercury in water at trace level is challenging.The direct propylation-purge and trap-gas chromatography-cold vapor atomic fluorescence spectrometry (DP-PT-GC-CVAFS) has been largely applied to determine MeHg in various water samples,whereas matrix interference cannot be avoid during the analysis,resulting in difficulties in further development and application of this method.This study evaluated several factors influencing the analysis of alkylmercury by DP-PT-GC-CVAFS,e.g.,dissolved organic matter (DOM),sulphideion,and chloridion in water.The results showed that all three factors have interference on the propylation reaction of alkylmercury,especially for MeHg.Moreover,MeHg and EtHg can be found when the level of Hg2+ in water is over 25 ng·L-1 (sample volume:40 mL);approximately 0.06％～0.09％ and 0.1％ Hg2+ will be transformed into MeHg and EtHg during the direct propylation,respectively.Overall,the direct propylation can be used to analyze alkylmercury for waters with low interference,e.g.,tap water,reservoir water,river water,and underground water,but not for tainted waters and/or waters with high concentrations of Hg2+.Therefore,to reduce the interference and precisely detect alkylmercury,distillation is a necessary step before the propylation (removal rate as high as 98％).%烷基汞(甲基汞和乙基汞)是中国污水排放标准、工业废水排放标准和地表水环境质量标准的重要指标,水中的烷基汞处于痕量水平,其分析检测是目前的难点之一.直接丙基化衍生化-吹扫捕集-气相色谱-冷原子荧光光谱法(DP-PT-GC-CVAFS)能快速、高效分析部分环境水样中的甲基汞,是较为理想的分析方法,但该方法在丙基化过程中易受到水中部分基质的干扰,不利于该方法的推广和应用.文章分析了影响水样丙基化反应的干扰因素,表明有机质、C1-和硫化物均会对甲基汞和乙基汞的丙基化衍生化产生干扰,且对甲基汞的影响更大.此外,Hg2+含量较高的水样在丙基化衍生化过程中会生成甲基汞和乙基汞,影响分析结果的准确定量.当水样中Hg2+超过25 ng·L-1时(进样量40 mL),直接衍生化会导致0.06％～0.09％的Hg2+转化为甲基汞,且甲基汞的生成率随Hg2+含量增大呈减小趋势;同时衍生化过程中约有0.1％的Hg2+转化为乙基汞,这将严重干扰水样中低含量乙基汞的准确定量.直接丙基化衍生化方法对于基质干扰较少的地表水(自来水、水库水、江水、地下水等)均能取得良好的分析效果,但并不适用于基质干扰严重和Hg2+含量较高的其他自然水体,衍生化前进行蒸馏处理可以高效和稳定去除水中Hg2+上(去除率98％)并消除其他基质的干扰,对多种水体具有普遍适用性.