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

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. Two water samples from pipe network were collected and added 10 microg/L of THMs mixed standards and 10 microg/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, 7 days, 14 days, 21 days and 30 days were measured by the concentration of THMs and HAAs, compared the changes of targets concentration with holding time. 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. 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.