三卤甲烷和卤乙酸测定中样品保存时间与其在萃取液中稳定性研究

Determination of trihalomethanes and haloacetic acids in the sample holding time,and their stability in the extract

目的研究水样中三卤甲烷(THMs:氯仿、二溴一氯甲烷、二氯一溴甲烷和溴仿)和卤乙酸(HAAs:一溴乙酸、二溴乙酸、一氯乙酸、二氯乙酸、三氯乙酸和一溴一氯乙酸)浓度随保存时间的变化及其在萃取液中的稳定性。方法采集2份管网末梢水,分别加入10μg/L三卤甲烷混标和10μg/L卤乙酸混标,于采样后的当天及3、7、14天以美国EPA551.1和552.3法测定THMs和HAAs浓度,比较其随样品保存时间的变化;加入混标的萃取液在保存的当天及7、14、21、30天时分别测定THMs和HAAs浓度,比较萃取液中目标物浓度随时间的变化。结果样品保存时间是影响目标物浓度的重要因素,目标物浓度随保存时间延长明显降低;萃取液中的目标物浓度除二氯乙酸下降外,在测试期内均较为稳定。结论样品保存时间对THMs和HAAs测定影响较大。因此,建议样品在采集当天进行测定或完成前处理;除二氯乙酸外,保存于萃取液中的目标物浓度在萃取物中可稳定30天以上。

Objective The purpose of this study is to investigate the changes of concentration of trihalomethanes （ THMs： chloroform,bromodichloromethane,chlorodibromomethane,bromoform） and haloacetic acids （ HAAs： monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, dibromoacetic acid, trichloroacetic acid, bromochloroacetic acid） in water samples with holding time and their stability in extract. Method Two water samples from pipe network were collected and added 10μg /L of THMs mixed standards and 10μg /L of HAAs mixed standards respectively. The concentrations of THMs and HAAs were measured by U. S. EPA methods 551. 1 and 552. 3 on the day after sampling,3 days,7 days and 14 days,and compared the changes with holding time. The extract with THMs or HAAs mixed standards in the preserving of the day,7days,14days,21days and 30 days were measured by the concentration of THMs and HAAs,compared the changes of targets concentration with holding time. Results Impact of sample holding time is an important factor in the concentration of the targets which significantly decreased with the extension of the time. The concentration of targets in extract except drichloroactic acid,keep stable in the periods of measurement. Conclusion Sample holding times have a greater impact on the determination of THMs and HAAs,therefore,we suggest that samples be measured or finished pretreatment on the day when sample was collected. In addition to drichloroacetic acid,the concentration of other targets in the extract can be stable for more than 30 days.