Use of gas chromatography–mass spectrometry–olfactometry and a conventional flask test to identify off-flavor compounds generated from phenylalanine during chlorination of drinking water

Abstract

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 N-labeled phenylalanine suggested that PAC reductively decomposed trichloramine into N 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).

Modeling chloramine stability and disinfection byproduct formation in groundwater high in bromide

“…Because a substantial portion of bromamines decay and release ammonia within a few hours, the NHCl₂, NCl₃, and free chlorine that persisted initially were likely able to tie‐up a portion of the free ammonia released (Figure S4). While ratios >5:1 form NHCl₂ and NCl₃ that can cause taste and odor problems, the maximum NHCl₂ and NCl₃ simulated concentrations for all conditions were 0.16 mg‐Cl₂/L and 0.012‐Cl₂/L, respectively, which would not be expected to cause aesthetic issues (Figure S4) (Matsushita et al, 2017; Suffet et al, 2004). However, at a lower pH, these odorant levels would be higher and could be problematic.…”

The Status Quo of Causal Substance Exploration for Fishy Odor in Raw Water for Taps

“…That is to say, GC-O enables us to conduct sensory and instrumental analysis simultaneously. For instance, Matsushita et al utilized GC-O-MS and identified N-chlorophenylacetaldimine and 2-chloro-2-phenylacetaldehyde as the odorants responsible for the off-flavor that had been generated by chlorination [92]. Employing MVA or GC-O, or using them in combination is a competent approach to determine a candidate chromatographic peak of fishy odorants.…”

Amino Acids as Potential Precursors to Odorous Compounds in Tap Water during Spring Runoff Events

“…For example, previous studies of laboratory chlorination of mg/L of Phe have identified N-chlorophenylacetaldimine with an odor threshold of 3−4 μg/L, and it has been linked with odor events in drinking water. 36,42 However, AAs make up a small portion of the total organic matter present in water, and thus a change in AA concentration may not result in changes to common water quality parameters which are used by operators to guide water treatment performance. No study has systematically investigated the occurrence of AAs in source water and odor profiles in home taps, because odor events are unpredictable.…”

“…Previous studies have demonstrated that laboratory chlorination and chloramination of AAs can produce aldehydes, N -chloroaldimines, and nitriles, which are odor-causing compounds that are often characterized as chlorinous odors. − ,,,− Compounds formed from AAs, particularly phenylalanine (Phe), leucine (Leu), isoleucine (Ile), and valine (Val), have been suggested as sources of odor concerns because their odor thresholds are as low as 150 ng/L. ,,, Several studies reported that AAs in environmental water occurred at ranges of 500 to 30,000 ng/L. ,,, Environmental levels of AAs in source water could potentially produce odorous DBPs at levels above the odor threshold during chlorination. For example, previous studies of laboratory chlorination of mg/L of Phe have identified N -chlorophenylacetaldimine with an odor threshold of 3–4 μg/L, and it has been linked with odor events in drinking water. , However, AAs make up a small portion of the total organic matter present in water, and thus a change in AA concentration may not result in changes to common water quality parameters which are used by operators to guide water treatment performance. No study has systematically investigated the occurrence of AAs in source water and odor profiles in home taps, because odor events are unpredictable.…”