Stir Bar Sorptive Extraction: A New Way to Extract Off-Flavor Compounds in the Aquatic Environment Application

The objective of this study was to analyze organic off-flavors in water by gas chromatography/mass spectrometry (GC/MS) using Stir Bar Sorptive Extraction (SBSE). Six compounds were quantitatively determined using Selected Ion Monitoring (SIM): 2-methylisoborneol (MIB), geosmin, 2,4,6-trichloroanisole, 2,3,6-trichloroanisole, 2,3,4-trichloroanisole and 2,4,6-tribromoanisole. The Limit of Quantification (LOQ) was found to be from 0.1 ng/L to 0.2 ng/L for haloanisoles, 0.5 ng/L for geosmin and 1 ng/L for MIB. Relative standard deviation at the quantification limit ranges from 7% to 14.6%. Recovery was evaluated by spiking real water samples. It ranged from 80% to 120% depending on the compound. GC/MS detection in the Stir Bar Sorptive Extraction: A New Way to Extract Off-Flavor Compounds in the Aquatic Environment Application scanning mode combined with olfactometry were used for qualitative analysis in order to characterize new odorous compounds. Using this technique, it was possible to extract and analyze more than 20 samples a day. Introduction Complaints received by water companies are most often due to bad taste and odors in drinking water. Furthermore, the presence of these unpleasant tasting but otherwise harmless compounds can be taken as unsafe water by the consumer. In most cases, complaints concern chlorine and earthy/musty smelling compounds. A better understanding of the chemical causes of taste and odors in drinking water supplies would help in the control of taste and odor problems. For 30 years, it was commonly accepted that earthy/musty aromas in drinking water were associated with the presence of geosmin, MIB and/or haloanisoles [1, 2, 3]. MIB and geosmin have strong odors, which are detectable at extremely low thresholds. MIB has a woody or camphor odor, detectable at a threshold ranging from 5 to 10 ng/L, while geosmin has a characteristic earthy odor detectable in water at a threshold ranging from 1 to 10 ng/L [4, 5]. The presence of these compounds in water was previously associated with the presence of actinomycetes or their metabolic products [6, 7, 8] in raw water, as well as cyanobacteria and fungi [9, 10, 11]. Haloanisoles have a Food and Flavors musty odor at a low threshold. For instance, the threshold odor of 2,4,6-trichloroanisole ranges from 0.05 to 4 ng/L. Their formation is probably caused by microbiological methylation of halophenols during water treatment or during transport through the distribution system [12, 13, 14]. Halophenols are formed during chlorine disinfection of drinking water and some of them have been identified as natural halogenation products [15]. For a long time, the identification of these compounds in water has been a real analytical problem because they are odorous at very low concentrations. The main analytical method used to identify odorous compounds in water is Closed Loop Stripping Analysis (CLSA). With this method [16, 17], organic substances are released from the water sample in a hermetically sealed, closed circuit system, which uses air or inert gas at 40 °C to strip away the volatiles. These liberated substances are transferred to a very small amount of charcoal localized in the closed circuit. Finally, the organic substances are eluted from the charcoal with solvent and are analyzed by GC. “Purge and Trap” analysis is based on the same principles as CLSA, but it exhibits lower sensitivity and, therefore, is very useful for concentration levels above 100 ng/L. Nevertheless, these “stripping” techniques were not 2 Table 1. Analyzed Odorous Compounds Name Abbreviation Taste Odor threshold, ng/L CAS number 2-methylisoborneol MIB Earthy 5–10 N/A 2,4,6-trichloroanisole 2,4,6-TCA Musty 0.1–2 6130-75-2 2,3,6-trichloroanisole 2,3,6-TCA Musty 0.1–2 50375-10-5 Geosmin Geosmin Camphor 1–1