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SPE�GC�MS Analysis of Chloroform in Drinking Water

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SPE�GC�MS Analysis of Chloroform in Drinking Water
  SPE–GC–MS Analysis of Chloroformin Drinking Water M. L. Di Gioia 1 , A. Leggio 1 , A. Le Pera 1 , A. Liguori 1, & , A. Napoli 2 , C. Siciliano 1 1 Dipartimento di Scienze Farmaceutiche, Universita` degli Studi della Calabria, Via P. Bucci, Cubo 15/C,I-87036 Arcavacata di Rende (CS), Italy; E-Mail: A.Liguori@unical.it  2 Dipartimento di Chimica, Universita` degli Studi della Calabria, Via P. Bucci, Cubo 15/C, I-87036 Arcavacata di Rende (CS),Italy  Received: 4 March 2004 / Revised: 25 May 2004 / Accepted: 7 June 2004Online publication: 5 August 2004  Abstract In this paper we report a method based on solid-phase extraction (SPE) and subsequent analysis by gas chromatography combined with mass spectrometry for determination of chloroform in potable water. The affinity of chloroform for the resin enables almost completerecovery of the analyte. The analytical method proposed enables evaluation of chloroformlevels down to 0.295  l g L  ) 1 . The procedure is characterized by lack of interferences, in fact theGC–MS analysis reveals the presence of only one peak, that of chloroform. Use of CDCl 3  aslabelled internal standard also makes the procedure suitable for use as a reference analyticalmethod for quantification of chloroform in drinking water. Keywords Gas chromatography-mass spectrometry Solid-phase extractionChloroform and trihalomethanesPotable water  Introduction Use of chlorine to disinfect surface wa-ter [1] produces volatile halogenated or-ganic by-products [2]. Among these, themost important are trihalomethanes(THM), haloacetic acids (HAA), andhaloacetonitriles (HAN), all compoundssuspected of having toxic, mutagenic,carcinogenic, and/or teratogenic effects.Studies in vitro have demonstrated thatchlorinated drinking water has genotoxicand mutagenic properties [3–10] althoughno definitive information about thegenotoxic activity of chlorinated drinkingwater in in-vivo tests can be found inliterature.Over the last three decades the harm-ful effects of chlorine disinfection havebeen a major topic in the field of drink-ing-water quality control. Althoughmuch effort has been devoted to the de-sign of valuable analytical procedures,development of simpler and more usefulmethods characterized by high sensitivity,the possibility of automation, and lack of interferences are the current challenge.Determination of trihalomethanes indrinking water has already been achievedby use of several procedures, includingliquid–liquid extraction [4, 11], directaqueous injection [12, 13] (DAI), head-space techniques [11, 14–18], and purge-and-trap [19–24] combined with solid-phase microextraction [25–29] (HS– SPME). In the literature it is reportedthat macroporous resins can be used toeliminate dissolved organic matter indrinking water [30]. These resins alsohave excellent retention capacity towardTHM in chlorinated drinking water.Because of this peculiar behaviour of the resins we sought to achieve qualita-tive and quantitative determination of chloroform by adsorption of the analyteon the resins using solid-phase extraction(SPE) [31–33]. The aim of the studywas application of SPE–GC–MS as astraightforward method for analysis of chloroform in drinking water. The use-fulness of the proposed procedure wasevaluated in the context of a programinvestigating THM concentrations indrinking water in Crotone (Italy). Experimental Reagents Standards and blanks were preparedfrom freshly double-distilled water(HPLC grade, Sigma–Aldrich, Milano,Italy). Extra-pure grade  n -pentane wasprepared by a standard procedure. Envi18 columns were purchased from Supelco(Milano, Italy). The resin was pretreatedbefore use as recommended by the sup-DOI: 10.1365/s10337-004-0387-5 2004 ,  60  , 319–322 0009-5893/04/09    2004 Friedr. Vieweg & Sohn/GWV Fachverlage GmbHOriginal Chromatographia  2004 , 60, September (No. 5/6)  319  pliers. THM standards (CHCl 3 , CHBr 3 ,CDCl 3 , CHCl 2 Br, CHClBr 2 ) were pur-chased from Sigma–Aldrich.  Water Source Water samples were collected from dif-ferent areas of the municipal distributionsystem of nineteen municipalities in thedistrict of Crotone (Calabria, Italy).Water samples were collected in glassbottles without headspace. Samples weretransported to the laboratory on ice andstored at 4   C before analysis. Samplescan be kept under these conditions forseven days. Standard Solutions Two standard solutions of 148  l g mL ) 1 commercially available chloroform(solution A) and CDCl 3  (solution B) wereprepared in methanol. A third standardsolution of 1184  l g mL ) 1 chloroform(solution C) was prepared in pentane.Five concentration levels of chloroformwere prepared using solution C (Stock 1:59, 5.9, 0.059, 4.13  ·  10 ) 3 , and2.64  ·  10 ) 3 l g mL ) 1 ). Five standards of water fortified with chloroform (Stock 2:59.2, 37.0, 29.6, 14.8, and 7.4  l g L ) 1 )were prepared from solution A. Solid-Phase ExtractionProcedure Among the different SPE adsorbents, C 18 was chosen because it is more suitable forretention of THM. To optimize elutionfrom the Envi 18 cartridge diethyl etherand pentane were tested as solvents.Volumes between 1 and 10 mL were usedfor each solvent; 5 mL was sufficient forcomplete elution of the analytes. Becausepentane afforded cleaner extracts it wasselected for all SPE experiments. Beforeuse, all Envi 18 cartridges (12 mL, 2 g)were washed with 2 mL acetonitrile and2 mL distilled water. Water samples (1 L)were then passed through the cartridges,at a flow-rate of 15 mL min ) 1 , by use of aconstant flow of dry nitrogen. (The vol-ume of water selected for analysis was acompromise between obtaining lowdetection limits and achieving a reason-able analysis time.) Retained organiccompounds were eluted from thecartridge by use of 5 mL pentane at aflow-rate of 2 mL min ) 1 . The obtainedextracts were dried over sodium sulphate. Gas Chromatographic Systemand Conditions GC–MS analyses were performed with anHP5972A mass spectrometer linked to aHP5890A series II gas chromatograph(Agilent Technologies, Palo Alto, CA,USA) equipped with a 30 m  ·  0.25 mmi.d. HP-5MS (5% phenyl poly-dimethylsiloxane) capillary column. He-lium, at a flow rate of 1 mL min ) 1 wasused as carrier gas. Sample injection of 1  l L samples was performed in splitlessmode. The column oven temperature wasmaintained at 40   C for 4 min then pro-grammed at 16   C min ) 1 to 280   C whichwas held for 5 min. The injection portand detector temperatures were 250 and280   C, respectively. The mass spec-trometer was operated at 1000 resolutionin electron-impact positive ionizationmode (EI+), electron energy 70 eV;scanning was from 35 to 450  l ma at ascan speed of 1 s decade ) 1 and with 0.2 sinter-scan time. The source temperaturewas 200   C. Quantitative GC–MS anal-ysis was performed by detecting the tar-get compounds by single-ion monitoring(SIM). Identification of the organiccompounds was performed by comparingEI spectra and chromatographic reten-tion times with those of commerciallyavailable authentic reference compounds.For procedural quality assurance blanksand reference samples were processed inthe same manner as water samples.  Validation Calibration for water samples wasachieved by analysis of five concentrationlevels (Stock 2), in the presence of aconstant amount (30  l g L ) 1 ) of CDCl 3 .CHCl 3 /CDCl 3  peak area ratios wereproportional to concentration for allsamples with good correlation coefficients(0.993–0.999). The detection limit was5  l g L ) 1 , as determined by use of a typ-ical calibration graph obtained fromStock 2 solutions (  y ¼ 0.9405 x  + 0.0272, R 2 ¼ 0.9991). The efficiency of recoveryof chloroform and the precision of theanalytical method were tested by fivefoldanalysis of the same sample of waterblank fortified with CHCl 3  (30  l g L ) 1 ) inthe presence of the same amount of CDCl 3  added as standard before the SPEextraction. The recovery of chloroformby SPE was estimated to be 96.5%(Table 1).The linearity and repeatability of theSPE–GC–MS method were investigatedby fivefold analysis of each level of for-tified water standard blanks (Stock 2,Fig. 1). Because, according to WHO, themaximum permissible level of chloroformin drinking water is 30  l g L ) 1 , and thismethod was linear within 0.295  l g L ) 1 and 2.5 mg L ) 1 , the optimum amount of water sample for analysis was 1000 mL. Table 1.  Recovery of CHCl 3  from fortifiedwater blanks (30  l g L ) 1 CHCl 3 ) by use of SPEResponse ratioGC–MS systemAmount*1 0.9368 29.112 0.9346 29.043 0.9336 29.014 0.9353 29.065 0.9343 29.03*Estimated concentration of CHCl 3  ( l g L ) 1 ;  y  = 0.9405 x  + 0.0272,  R 2 = 0.9991). 00.511.522.50123 Series 1Series 2Series 3Series 4Series 5 y = 0.9497x- 0.0958R 2  =0,9833y = 0.8917x- 0.0899R 2 = 0,9833y = 0.9003x- 0.0908R 2  =0.9833y = 0.9895x- 0.0998R 2  =0.9833y = 0.9344x- 0.0888R 2  =0.9826 Fig. 1.  Linearity and repeatability of SPE–GC–MS analysis 320  Chromatographia  2004 , 60, September (No. 5/6) Original  Results and Discussion The excellent retention of organic com-pounds by some resins [30] was thestarting point for preliminary evaluationof the recovery of chloroform by SPE.Initial experiments were performedusing water blanks fortified with stan-dard solutions of chloroform. A con-stant volume (5 mL) of pentane wasused to elute this volatile compoundtrapped on an Envi 18 column. (Thecolumns were chemically and mechani-cally stable at pH typical of the watersamples.) Percolation of water samplesthrough the columns at applied pressuresof ca 1 bar N 2  and a flow rate of 15 mL min ) 1 , resulted in very goodextraction efficiency (the estimatedrecovery was 96.5%) for the volatileorganic compound, without contamina-tion. The sensitivity of the quadrupole asmass filter was tested in full scan andsingle-ion monitoring (SIM) modes. Infull-scan mode five solutions of chloro-form in pentane (Stock 1) were analyzedand the lowest concentration of chloro-form that could be evaluated was0.059  l g mL ) 1 pentane. The limit of detection was calculated as the minimumconcentration providing a chromato-graphic signal three times higher thanbackground noise. This value ensuresthat the lowest detectable limit is0.295  l g L ) 1 water. SIM analysis of ex-tracts performed by detecting the twomost abundant ions of the correspond-ing ion cluster ( m / z  83 and 84) revealeda linear trend of total ion current (TIC)for the selected ions. The linearity ob-served for GC–MS analysis of chloro-form in the starting water solutions wasin the range 0.295  l g L ) 1 to 2.5 mg L ) 1 .All tests performed on standard solu-tions of CHCl 3  and CDCl 3 , the last usedas internal standard, showed recovery of SPE extraction was high and reproduc-ibility was excellent. Fortified blank wa-ter (30  l g L ) 1 CHCl 3 ) was analyzed fivetimes and the concentration level(Medium Value, MV) determined was29.05 ± 0.038  l g L ) 1 .In a typical analytical procedure a 1-Lwater sample spiked with 100  l L CDCl 3 /CH 3 OH (solution B) was percolatedthrough the Envi 18 column at the opti-mum flow rate (15 mL min ) 1 ). Elutionwith pentane afforded an enriched chlo-roform-containing fraction that wassubjected to GC–MS analysis. To ensurethe absence of trichloroacetic acid in thewater samples the SPE organic extractswere also treated with an ethereal solu-tion of diazomethane [34] before GC–MSanalysis. This test was necessary becausethe quantitative SPE–GC–MS responsetoward chloroform could be compro-mised by decarboxylation of any trichlo-roacetic acid, leading to formation of isobaric ions ( m / z  83, 85) under theexperimental conditions used for MS.GC–MS analysis performed onorganic extracts obtained in this wayrevealed the presence of only one peak Table 2.  Results from analysis of water samples collected from different locations in the municipaldistribution system of the district of CrotoneCrotonedistrict( l g L ) 1 )Sample CHCl 3 ( l g L ) 1 )CrotonedistrictSample CHCl 3 Area 1 1 39.17 Area 8 1 16.192 11.66 2 2.503 13.92 Area 9 1 7.494 7.02 2 28.435 45.44 3 27.236 16.06 Area 10 1 19.057 4.19 Area 11 1 14.878 11.10 Area 12 1 3.879 18.70 Area 13 1 <0.2910 <0.29 Area 14 1 40.1511 6.33 2 4.71Area 2 1 45.67 Area 15 1 6.49Area 3 1 16.96 Area 16 1 14.03Area 4 1 <0.29 Area 17 1 17.59Area 5 1 6.60 2 9.00Area 6 1 12.00 Area 18 1 12.222 25.44 Area 19 1 <0.29Area 7 1 13.40 1.50 1.60 1.70 1.80 1.90 2.00 2.10 2.20 2.30 2.40 2.50 2.60 2.70 1.53 1.50 1.60 1.70 1.80 1.90 2.00 2.10 2.20 2.30 2.40 2.50 2.60 2.70002004006008001000120014001600020040060080010001200140016002004006008001000120014001600 Time(min)Time(min) AbundanceAbundanceAbundance  1.53 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 m/zScan 24 (1.527 min)8483 (a)(b)(c) Fig. 2.  Typical results from SPE–GC–MS analysis of a water sample: (a) ion chromatogram of   m / z 83; (b) ion chromatogram of   m / z  84; (c) mass spectrum obtained from the water sample at retentiontime 1.53 min under SIM conditions Original Chromatographia  2004 , 60, September (No. 5/6)  321  corresponding to the chloroform. Toconfirm the absence of other THM andtrichloroacetic acid, chromatograms ob-tained from the organic extracts werecompared with that obtained from anal-ysis of a standard solution containingtrichloroacetic acid methyl ester andthe THM. Peaks from the THMCHCl 2 Br ( t R ¼ 2.43 min), CHClBr 2 ( t R ¼ 4.13 min), CHBr 3  ( t R ¼ 6.11 min),and CCl 3 COOCH 3  ( t R ¼ 6.75 min) werenot present in the chromatogram of thewater sample examined. This methodthus enables exclusive extraction of chloroform from drinking water, ensur-ing lack of contaminants and interfer-ences.Results obtained from analysis of different water samples are reported inTable 2. Analysis of the municipaldrinking water from the district of Cro-tone revealed fluctuating concentrationsof chloroform. Water samples were col-lected from different areas of the muni-cipal distribution system. Samplinglocations were selected to represent theoverall quality of the distribution system.Duplicate samples were collected frommunicipalities characterized by predomi-nant use of surface water in their distri-bution system.Chloroform levels throughout theone-year study ranged from 3.87 to46  l g L ) 1 . A typical SPE–GC–MS re-sponse obtained from a water sample isreported in Fig. 2.The presence of chloroform in thedrinking water analyzed is a consequenceof the general use of surface water by themunicipalities in the distribution system.The maximum permissible level of 30  l g L ) 1 chloroform recommended bythe World Health Organization was ex-ceeded in a few instances only. Conclusions The Envi 18 columns used for SPE enablereproducible extraction with an excellentrecovery of chloroform from drinkingwater.This method, characterized by goodsensitivity, is easy to perform and couldbecome established as a new analyticalprocedure. Recovery of chloroform(96.5%) is greater than that normallyobtained by other methods, for exampleliquid–liquid extraction, for whichrecovery is 70–80% [4]. The precision of this new analytical method enables eval-uation of chloroform levels down to0.295  l g L ) 1 , and use of CDCl 3  as a la-belled internal standard makes the pro-cedure discussed here suitable for use as areference analytical method for quantifi-cation of chloroform in drinking water.This analytical procedure has signifi-cant advantages over conventionalmethods used for determination of chlo-roform in matrixes other than water [35,36]. In fact, adsorption of chloroform bythe resin is specific and, consequently, nointerferences are observed. The affinity of chloroform for the resin enables nearlycomplete recovery of the dissolved THM.In the light of these considerations thetime required to process a single watersample becomes acceptable. 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