| Malodorous substances are the most common pollutants in water pollution,which can cause an undesirable smell at very low concentration.Nitrogen and sulfur compounds are the most common malodorous substances.As an effective analytical method for separation and determination of volatile compounds,gas chromatography(GC)has the advantages of high sensitivity,high selectivity,and fast analysis speed,etc.However,traditional GC detectors have the relatively large size,high gas and power consumption,making them only suitable for laboratory analysis.Dielectric barrier discharge(DBD)microplasma-optical emission spectrometry(OES)has the advantages of simple structure,stable discharge and strong excitation ability,as an alternative for GC detector gradually.Compared with traditional GC detectors,DBD-OES detector has the characteristics of high portability,high sensitivity and low energy consumption,which can achieve multi-element analysis and become a portable GC detector.Because the concentration of nitrogen and sulfur substances in water is lower than the detection limit obtained by GC-DBD-OES system with direct injection,enrichment treatment is required prior to detection.In this study,DBD-OES was used as GC detector to establish the GC-DBD-OES system.When combined with ultrasonic nebulization-activated carbon enrichment pretreatment method,GC-DBD-OES system was applied to achieve the determination of nitrogen and sulfur compounds in environmental water.(1)According to the principle and discharge structure of DBD,DBD-OES was designed and served as GC detector.With dimethyl sulfide,ethyl mercaptan,dimethyl disulfide,methyl thioglycolate and trimethylamine as analytes,the structure of DBD was optimized.The effects of the input voltage and carrier gas flow rate on the OES intensity were investigated,and GC conditions were optimized to achieve the separation and detection of mixture under temperature programming.Under the optimized experimental conditions,with 384.94 nm as analytical line,the limits of detection(LOD)of the GC-DBD-OES system for methyl sulfide,ethyl mercaptan,dimethyl disulfide,methyl thioglycolate and trimethylamine are 0.033,0.085,0.017,0.0026 and 0.31μg,respectively,and the precision(RSD)values are 6.2%,9.1%,7.5%,4.3%and 3.9%,respectively.The GC-DBD-OES system has been successfully used for the direct separation and detection of nitrogen and sulfur compounds.(2)Based on the developed GC-DBD-OES system combined with a new type of solution ultrasonic nebulization-activated carbon enrichment pretreatment device,trace nitrogen and sulfur compounds including dimethyl sulfide,ethyl mercaptan,methyl thioglycolate,trimethylamine and ammonia in water were enriched and detected.In the experiment the thermal desorption conditions were optimized,and the effects of the thermal desorption temperature and thermal desorption time on the OES intensity were investigated.Under the optimal experimental conditions,the limits of detection(LOD)of methyl sulfide,ethyl mercaptan,methyl thioglycolate,trimethylamine,ammonia in water are 0.48,1.4,0.47,2.4 and 1.9 μg L-1,respectively,and the precision(RSD)values are 2.7%,8.7%,2.6%,5.8%and 6.9%,respectively.The present system is used to carry out the spiked recovery experiment on environmental water samples,and the recovery is within 80%-92%,indicating that the analytical system possesses a favorable accuracy.In summary,the nitrogen and sulfur compounds were enriched by ultrasonic nebulization-activated carbon enrichment method,and detected by DBD-OES coupled to GC.It is believed that the application scope of GC-DBD-OES will be further expanded to achieve the specific detection of other elements and molecules in the near future.At the same time,it is possible to develop a portable GC detector for field analysis... |
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