EPA Method 524.2 is an approved method for analyzing Total Trihalomethanes (TTHMs) (40 CFR 141.131(b)(1)). Must water samples being analyzed for TTHMs using EPA Method 524.2 be acidified with hydrochloric acid at the time of collection?
Samples being analyzed for TTHMs where sodium thiosulfate is used as the dechlorinating agent do not need to be acidified with hydrochloric acid at the time of collection. However, if ascorbic acid is used as the dechlorinating agent, then the samples must be acidified at the time of collection. The water system should check with the laboratory to see which dechlorinating agent the lab is using when the sample bottles are prepared. When EPA Method 524.2 is used for VOC samples, then it is necessary to acidify the samples at the time of collection.
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