Sequential analysis of dimethyl sulfur compounds in seawater

Available online at www.sciencedirect.comCHINESEScienceDirectC HEMICALL .ETTERSELSEVIERChinese Chemical Letters 18 (2007) 99-102www.elsevier.com/locate/ccletSequential analysis of dimethyl sulfur compounds in seawaterMeng Li, Dong Xing Yuan *, Quan Long Li, Xiao Ying JinState Key Lab of Marine Environmental Science, Xiamen University,Environmental Science Research Centre of Xiamen University, Xiamen 361005, ChinaReceived 15 February 2006Abstractpropionate (DMSP) and dimethylsulfoxide (DMSO), in seawater samples has been developed. Detection limit of 2.5 pmol of DMS in25 mL sample, corresponding to 0.10 nmol/L, was achieved. Recoveries for dimethyl sulfur compounds were in the range of 68.6-78.3%. The relative standard deviations (R.S.D.s) for DMS, DMSP and DMSO determination were 3.0, 5.4 and 7.4%, respectively.C 2006 Dong Xing Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.Keywords: Dimethylsulfide (DMS); Dimethylsulfoniopropionate (DMSP); Dimethylsulfoxide (DMSO); Purge and trap; Microwave iradiation;Sequential analysisLiquid extraction [1], cryogen-trap [2], isotopic dilution [3,4] and solid phase microextraction [5] had been used todetermine dimethylsulfide (DMS) in seawater. However, those methods are laborious, high detection limit or costly. Inorder to measure dimethylsulfoniopropionate (DMSP), the most popular but time consuming method is throughconverting DMSP into DMS by cold alkali treatment [6]. It had been found that microwave irradiation could acceleratethe process of DMSP hydrolysis, and thus provide a good approach to determine DMSP [7]. For measurement ofdimethylsulfoxide (DMSO) in seawater, it is needed to reduce DMSO into DMS. Titanium trichloride [8], stannouschloride [9] and enzyme [10] had been used as reducing reagents, however, these methods required complexexperimental procedures and remained analytical interferences. With HCl [1] or iron chloride [12], sodiumborohydride reduction of DMSO could proceed smoothly and efficiently. Sim6 et al. [13,14] reported a sequentialprocedure to measure DMS/DMSP/DMSO in seawater, but the method needed several hours for sample pretreatmentbefore the determination.The objective of this study was to establish a rapid and reliable method for the sequential determination of dimethylsulfur compounds in seawater.1. ExperimentalAn ENCON purge-and-trap system (EST Co., OH, USA) was coupled to a CP3800 gas chromatograph (Varian Co.,CA, USA) equipped with pulsed fame photometric detector (PFPD) in sulfur mode. The temperatures of the injectionCorresponding author.E-mail address: yuandx @ xmu.edu.cn (D.X. Yuan).中国煤化工1001-8417/$ - see front matter◎2006 Dong Xing Yuan. Published by EIsevier B.V. onCHCNMHGAll rights reserved.doi: 10.1016/.cclet.2006.1 1.005100M. Li et al./Chinese Chemical Letters 18 (2007) 99 -10225mL seawater samples↓DMS, DMSP and DMSO55 mL /min N2 purged 18min,trapped by VOCARB 3000 (10cmx 4 mm,Carbopack B/Carboxen M 1000& 1001) at 30°C.→determined DMSDMSP and DMSOAdded 0.1g NaOH, microwave iradiated6min under 200W, cooled and neutralized,converted DMSP to DMS.determined DMSAdded 2 mL 2% NaBH4,DMSOconverted DMSO to DMS.一→determined DMSFig. 1. Scheme of sequential determination of DMS, DMSP and DMSO in seawaters.2118、I5Purge flow rate区1一r - 40mL/min-✧- 45mL/min士50mL/min- 55mL/min10152025303:;4(4:;50Purge time (min)Fig. 2. Effects of purge time and purge flow rate on DMS (25 mL, 3.5 nmol/L) signal.port and the detector were set at 100 and 220 °C, respectively. The flow rate of the carrier gas N2 was 5 mL/min.Splitless injection model was selected and a DB-624 column (70 m X 0.53 mm, de= 3 μm, J&W Scientific, CA,USA) was adopted. The column temperature was kept at 100 °C. The microwave system was National NN-8552WFoven. All the reagents were above analytical grade.Sample was filtered through a GF/F membrane. DMS, dissolved DMSP (DMSPd) and dissolved DMSO (DMSOa)in the filtered seawater were analysed following the procedure ilustrated in Fig. 1.0「25 [无王玉汪王文18十20 F爹18 t12首126↓(a(tc)244(80中国煤化工1 24→30Microwave time (min)Oven heating Time (:MYHCNMHGrime(hou)Fig. 3. Comparison of three methods for DMSP hydrolysis. (a) Microwave iradiation, (b) oven heating and (C) cold alkali treatment.M. Li et al./Chinese Chemical Letters 18 (2007) 99 -102101//HCl added◆1:1HCl 40μL .- <- 1:1HCl 30uL- 0- 1:1HCl 35uL0.02.040.06 .NaBH 4(g)Fig. 4. Effect of amount of NaBH4 and HCl used on the signal of DMSO (20 mL, 2.5 nmol/L) reduction.Table 1Linear range, detection limit, regression equation, correlation cofficient, recovery and R.S.D. of the proposed methodDMSDMSP .DMSOLinear range (nmol/L, n=5)0.25- -20Regression equation"yIn= 2.054x+ 13.574y2= 1.3552x - 28.816yl"2= 1.981x + 53.332Correlation cofficient R20.99400.9991Detection limit (nmol/L)0.10.10Recovery (%)68.6-78.368.6-78.3 .R.S.D. (%, n=6)3.0.4“y and x represent the peak area and the concentration of the compound, respectively.Table 2The concentration of DMS/DMSP/DMSO of a surface seawater sample of Xiamen Bay (n= 3)DMS (nmol/L)DMSPa (nmol/L)DMSO, (nmol/L)4.15土0.121.79土0.090.34土0.022. Results and discussionFig.2 shows that after purging 18 min at a flow rate of 55 mL/min, the peak area of DMS reached the maximumvalue, and no detectable DMS was found in the successively purged samples. Fig. 3 demonstrates the comparison ofDMSP hydrolysis efficiencies in the same sample by microwave iradiation, oven heating treatment and cold alkalitreatment. The result showed that DMS peak area could reach the maximum after 6 min microwave irradiation, whileother two methods needed 100 min and 13 h, respectively. Hydrolysis with microwave irradiation was time savingcompared to the other two methods. Fig. 4 indicates that addition of 40 μL of 1:1 HCI and 0.04 g of NaBH4 was theoptimal choice for the reduction of DMSO. Table 1 summarizes the linear range, relative standard deviation (R.S.D.),detection limit and recovery of the proposed sequential determination method. Table 2 lists the concentration ofdimethyl sulfur compounds in a surface seawater sample collected from Xiamen Bay.3. Conclusion中国煤化工A rapid sequential analytical method for the determination of DMS,MYHCN M H Gr was dveloped.This method could be applied to the analysis of seawater samples.102M. Li et al./Chinese Chemical Letters 18 (2007) 99 -102AcknowledgementsThis work was supported by the grant (No. 200077022) from NNSF of China.References[1] B.C. Nguyen, A. Gaudry, B. Bonsang, G. Lambert, Nature 275 (1978) 637.[2] M.O. Andreae, W.R. Bamard, Anal. Chem. 55 (1983) 608.[3] R.G. Ridgeway, A.R. Bandy, D.C. Thornton, Mar. Chem.33 (1991) 321.[4] G.C. Smith, T Clark, K. Linda, et al. Anal. Chem. 71 (1999) 5563.[5] T Niki, T Fujinaga, MF. Watanabe, et al. J. Oceanogr. 60 (2004) 913.[6] R. Sim6, J.0. Grimalt, J. Albaiges, J. Chromatogr. A 655 (1993) 301.[7] M. Chen, H.Y. Li, D.X. Yuan, et al. Environ. Chem. 21 (2002) 183 (in Chinese).[8] R.P. Kiene, G. Gerard, Mar. Chem. 47 (1994) 1.[9] JA. Gibson, R.C. Garrick, H.R. Burton, et al. Mar. Biol. 104 (1990) 339.[10] A.D. Hatton, G. Malin, A.G. Mcewan, et al. Anal. Chem.66 (1994) 4093.[11] M.O. Andreae, W.R. Barnard, Anal. Chem. 55 (1983) 608.[12] Kenshiro Ui, Mitsuru Abo, Akria Okubo, et al. Anal. Sci. 20 (2004) 223.. [13] R. Sim6, J.O. Grimalt, J. Albaiges, Anal. Chem. 66 (1996) 1493.[14] R. Simo, G. Malin, P.S. Liss, Anal. Chem. 70 (1998) 4864.中国煤化工MYHCNMH G .