Analysis of Three Dimethyl Sulfides in Freshwater Lakes Using Headspace Solid-Phase Microextraction-Gas Chromatography with Flame Photometric Detection  
[PERSON]  
1 Ningbo College of Health Sciences, Ningbo 315100, China; [EMAIL_ADDRESS] (Q.B. ); [EMAIL_ADDRESS] (J.L. ); [PERSON]ADDRESS] (L.J.) [PERSON]  
2 Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; [EMAIL_ADDRESS]  
[PERSON]  
1 Ningbo College of Health Sciences, Ningbo 315100, China; [EMAIL_ADDRESS] (J.L. ); [PERSON]ADDRESS] (L.J.) [PERSON]  
1 Ningbo College of Health Sciences, Ningbo 315100, China; [EMAIL_ADDRESS] (Q.B. ); [EMAIL_ADDRESS] (J.L. ); [PERSON]ADDRESS] (L.J.) [PERSON]  
2 Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; [EMAIL_ADDRESS]  
Correspondence: [EMAIL_ADDRESS]; Tel. : +86-25-8688224 222  
of DMSs in the water body is often high and can even cause it to be foul-smelling [7]. Follow-up monitoring studies have shown that DMSs, produced by the death and degradation of cyanobacteria accumulating in the shallow eutrophic Lake Taihu, was an odorous substance that triggered a water supply crisis in the city of Wuxi, Jiangsu Province of China, in 2007 [8], resulting in more than two million residents of the city being left without clean drinking water for up to a week. High concentrations of DMSs were detected in many freshwater lakes globally. In the United States, the maximum concentration of DMS in the Salton Sea lake was 11 umol/L throughout the year [9], while the concentrations of DMS and DMDS in Linsley Pond lake were as high as 5.3 \(\upmu\)g/L and 0.98 \(\upmu\)g/L, respectively [10]. Recent studies have shown that the DMS concentration in the water column of Yangcheng Lake, a shallow eutrophic lake, is significantly higher than that in deep-water lakes [11]. Therefore, DMSs have become a prevalent olfactory substance in freshwater bodies, including eutrophic lakes, reservoirs, and rivers [12; 13; 14]. The detection methods for odorants such as DMSs mainly include sensory and instrumental analyses. Sensory analysis methods include olfactory level description, and olfactory threshold and hierarchy analysis methods. Because the steps of sensory analysis are cumbersome, and the errors are large. Instrumental analysis is more often used for detecting complex olfactory substances. During the detection, preconcentration and instrument selectivity are key steps in the identification of DMSs, whose volatility and high reactivity pose a great challenge for accurate quantitative analysis. Current analytical methods for the determination of DMSs are based on gas chromatography (GC) with different detectors. Detectors such as flame photometric detectors (FPD), mass spectrometry detectors (MSD), sulfur chemiluminescence detectors (SCD), and pulsed flame photometric detectors (PFPD) are often used [15; 16; 17; 18; 19]. However, both PFPD and SCD are specific detectors that require sophisticated measurement techniques and are not commonly configured in laboratories, whereas MSD detectors are more expensive. Previous studies have shown that for the determination of DMSs in different environmental media, despite the use of expensive MSD detectors, the detection limit is of the same order of magnitude as other detectors and does not reflect a better quantitative advantage [20]. Compared to other detectors, FPD detector has better selectivity for the small molecules of sulfides and phosphides. Moreover, FPD detectors are routinely used in testing laboratories and are economical. In previous studies on sulfide detection using SPME and GC-FPD, only DMS was measured, and multiple dimethyl sulfides were not investigated [18]. The methods in other related studies were found to have an extremely low detection of DMTS in our research practice, so further improvement of the detection method is needed [19]. Therefore, the use of FPD detectors for the determination of DMSs is more generalizable.