美国环保局方法551使用pH值调整的氯化铵来保存氯化饮用水样本中的一系列挥发性消毒副产物（DBPs）。然而，在分析水合氯醛和氯化氰时，建议使用抗坏血酸作为防腐剂。加拿大卫生部最近的研究使用了一种改编自美国环境保护局方法551的方法来分析目标DBP。该方法基于甲基叔丁基醚（MTBE）萃取含有氯化铵防腐剂的水样，并在现场调整至pH 4.5。为了测定氯化氰，根据Sclimenti等人的说法，通过用抗坏血酸溶液代替氯化铵对该方法进行了改进。在对17个使用氯化、氯胺化和臭氧氧化的水处理设施进行调查时，对这两种方法进行了比较，以确定方法551的目标DBPs。 本文介绍了溴化DBP和其他次要DBP的比较数据。有人认为，在某些水中，抗坏血酸可能不是某些溴化和溴氯DBP的合适防腐剂，尤其是溴化乙腈。因此，进行了额外的研究，以评估溴化DBP物种在抗坏血酸存在下的稳定性。本文还对这些数据进行了介绍和讨论。

USEPA Method 551 uses ammonium chloride with pH adjustment for the preservation of a range of volatile disinfection byproducts (DBPs) in chlorinated drinking water samples. However, the use of ascorbic acid as a preservative has been recommended for the analysis of chloral hydrate and cyanogen chloride. A method, adapted from USEPA Method 551, was used in recent Health Canada studies for the analysis of target DBPs. The method was based on methyl t-butylether (MTBE) extraction of water samples containing ammonium chloride preservative and adjusted to pH 4.5 in the field. To determine cyanogen chloride, the method was modified by substituting the ammonium chloride with ascorbic acid solution according to Sclimenti et al. These two methodologies were compared for Method 551 target DBPs in a survey of 17 water treatment facilities using chlorination, chloramination and ozonation. This paper presents comparative data for brominated DBPs and other minor DBPs. It has been suggested that, in some waters, ascorbic acid may not be a suitable preservative for some brominated and bromo-chloro-DBPs, particularly the brominated acetonitriles. Therefore, additional studies were undertaken to evaluate the stability of brominated DBP species in the presence of ascorbic acid. These data are also presented and discussed.