Off-flavor in drinking water can be caused by transformation products (TPs) generated from organic compounds, such as amino acids, present during chlorination. However, the contributions of many of these TPs to overall off-flavor have not been quantified, mainly because the lack of appropriate chemical standards prevents sensory evaluation by means of a conventional flask test. In the present study, we used gas chromatography–mass spectrometry–olfactometry (GC-MS-O) to identify compounds responsible for the off-flavor generated by chlorination of an aqueous solution of the amino acid phenylalanine, and we propose a sensory evaluation procedure for quantification of the contributions of the identified TPs to the overall off-flavor, regardless of the availability of chemical standards of the TPs. GC-MS-O revealed that two TPs, N-chlorophenylacetaldimine and 2-chloro-2-phenylacetaldehyde, for which chemical standards are not commercially available, were the main components responsible for the off-flavor of the chlorinated solution. By using a sensory evaluation procedure involving a combination of GC-MS-O and a conventional flask test, we quantified the contributions of TPs to the overall off-flavor of the chlorinated solution. Approximately 60% of the off-flavor was attributable to free chlorine (13%), 2-chloro-2-phenylacetaldehyde (13%), trichloramine (12%) phenylacetaldehyde (11%) phenylacetonitrile (8%), and N-chlorophenylacetaldimine (2%). Treatment with powdered activated carbon (PAC) removed the off-flavor. Experiments with chlorination of ¹⁵N-labeled phenylalanine suggested that PAC reductively decomposed trichloramine into N₂ gas and adsorbed all of the other identified TPs. Superfine PAC (median diameter, 0.7 μm) removed the off-flavor more rapidly than normal-size PAC (median diameter, 8.0 μm).

中文翻译：

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使用气相色谱-质谱-嗅觉法和常规烧瓶试验来鉴定饮用水加氯过程中苯丙氨酸产生的异味化合物

饮用水中的异味可能是由氯化过程中存在的有机化合物（例如氨基酸）产生的转化产物（TP）引起的。但是，许多这些TP对总体味道的贡献尚未得到量化，这主要是因为缺乏适当的化学标准物，无法通过常规的烧瓶测试来进行感官评估。在本研究中，我们使用了气相色谱-质谱-嗅觉法（GC-MS-O）来鉴定导致氨基酸苯丙氨酸水溶液氯化而产生的异味的化合物，并提出了一种感官评估程序不管已确定的TP的化学标准如何，都可以用于量化已确定的TP对总体异味的贡献。GC-MS-O发现有两个TP，化学标准品不可商购的N-氯苯基乙醛亚胺和2-氯-2-苯基乙醛是造成氯化溶液异味的主要成分。通过使用结合了GC-MS-O和常规烧瓶测试的感官评估程序，我们量化了TP对氯化溶液总体异味的贡献。约60％的异味归因于游离氯（13％），2-氯-2-苯基乙醛（13％），三氯胺（12％）苯乙醛（11％）苯乙腈（8％）和N-氯苯基乙二胺（2％）。用粉末状活性炭（PAC）处理可去除异味。氯化实验¹⁵N标记的苯丙氨酸表明PAC将三氯胺还原分解为N ₂气体，并吸附了所有其他已确定的TP。超细PAC（中值直径0.7μm）去除异味的速度比正常尺寸PAC（中值直径8.0μm）更快。