Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry for the screening of potent swampy/septic odor-causing compounds in two drinking water sources in China

Abstract

Odor problems in drinking water, particularly swampy/septic odors, are normally triggered by a set of organic compounds with odor threshold concentrations (OTC) ranging from ng L À1 to mg L À1. With such a low level of OTC, it has long been a challenge to effectively determine the odor-causing compounds in highly complex samples. The Huangpu and Huai rivers, as source waters in south China, have exhibited continuous swampy/septic odor over the entire year, yet the corresponding odor-causing compounds remain unclear. In order to screen the odor-causing compounds in these two rivers, a method to simultaneously determine fifty-four frequently encountered compounds with categories of thioethers, aldehydes, pyrazines, benzenes and phenols, has been developed using comprehensive twodimensional gas chromatography with time-of-flight mass spectrometry (GC Â GC-TOFMS) based on liquid-liquid extraction. The results indicated that this method could allow the analysis of different categories of compounds without derivatization at considerably higher sensitivities. Four thioether compounds, including dimethyl disulfide, diethyl disulfide, propyl sulfide, and amyl sulfide, and one ether compound (bis(2-chloroisopropyl) ether) were at least detected in one of the source waters with a concentration higher than their OTC value, suggesting that these compounds might be the main compounds causing the swampy/septic odor. At the same time, other compounds, including pyrazine, pyridine, 2-methyl-phenol, 2-nitro-phenol, and 2,6-dimethyl-phenol, were detected with a concentration lower than their respective OTC value. The contribution of these compounds to the swampy/septic odor requires further evaluation.

Simultaneous removal of multiple odorants from source water suffering from septic and musty odors: Verification in a full-scale water treatment plant with ozonation

“…The first dimension (the column in the main GC oven) was configured as a commonly used a low polarity column, while the second dimension adopted a polar column for better separation of extracts. The specific operating conditions can be found in our previous study (Guo et al, 2015).…”

“…These water samples were transported to the laboratory immediately in an insulated box with added ice bags to maintain the temperature below 4 C. Sensory characteristics of the water samples were evaluated using FPA (APHA, 2005) immediately once received, and pre-concentration using liquid-liquid extraction (LLE) for odorant determination through GC Â GC-TOFMS analysis was completed within two days (Guo et al, 2015). Every batch of water sample was analyzed in duplicate, and the odorants' concentrations were the average values of the parallel analyses.…”

“…Fifty-four odorant standards of eleven groups, namely, aldehydes, benzenes, ethers, esters, indoles, ketones, pyrazines, pyridines, phenols, thioethers, thiols, etc., (Guo et al, 2015) were purchased at the highest level of purity from Sigma-Aldrich (USA). Stock solutions of 1000 mg/L for standards were prepared by diluting different standard solutions with HPLC grade methanol.…”

“…It is possible that different types of odorants may coexist in some source waters. For example, twenty odorants of eight categories with 2e3 orders of magnitude difference in odor threshold concentrations (OTCs) have been detected with a wide range of differences in concentration levels in Huangpu (HP) River source water in a water quality survey (Guo et al, 2015). Therefore, most odor events in drinking waters have been caused by multiple odorants (Khiari et al, 1995;Suffet et al, 1999).…”

Source-water odor during winter in the Yellow River area of China: Occurrence and diagnosis

“…In this study, 16 typical odorants were selected for quantification. The methodology used was developed in our previous study (Guo et al, 2015), the accuracy and precision of which was satisfactory.…”