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⁻¹ to μg L⁻¹. 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 two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × 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.