HS-SPME for the determination of volatile and semivolatile p, Artykuły naukowe, SPME i HS-SPME
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//-->Talanta 48 (1999) 451– 459Headspace solid phase microextraction (HSSPME) for thedetermination of volatile and semivolatile pollutants in soilsMaria Llomparta,*, Ken Lib, Merv FingasbDepartamento de Quimica Analitica Nutricion y Bromatologia, Facultad de Quimica, Uni6ersidad de Santiago de Compostela,E-15706Santiago de Compostela, SpainbEmergencies Science Di6ision, En6ironment Canada, En6ironmental Technology Centre,3439Ri6er Road, Ottawa, ON, CanadaReceived 3 April 1998; received in revised form 10 July 1998; accepted 3 August 1998aAbstractWe have investigated the use of headspace solid phase microextraction (HSSPME) as a sample concentration andpreparation technique for the analysis of volatile and semivolatile pollutants in soil samples. Soil samples weresuspended in solvent and the SPME fibre suspended in the headspace above the slurry. Finally, the fibre was desorbedin the Gas Chromatograph (GC) injection port and the analysis of the samples was carried out. Since the transfer ofcontaminants from the soil to the SPME fibre involves four separate phases (soil-solvent-headspace and fibre coating),parameters affecting the distribution of the analytes were investigated. Using a well-aged artificially spiked gardensoil, different solvents (both organic and aqueous) were used to enhance the release of the contaminants from thesolid matrix to the headspace. It was found that simple addition of water is adequate for the purpose of analysingthe target volatile organic chemicals (VOCs) in soil. The addition of 1 ml of water to 1 g of soil yielded maximumresponse. Without water addition, the target VOCs were almost not released from the matrix and a poor response wasobserved. The effect of headspace volume on response as well as the addition of salt were also investigated.Comparison studies between conventional static headspace (HS) at high temperature (95°C) and the new technologyHSSPME at room temperature ( 20°C) were performed. The results obtained with both techniques were in goodagreement. HSSPME precision and linearity were found to be better than automated headspace method andHSSPME also produced a significant enhancement in response. The detection and quantification limits for the targetVOCs in soils were in the sub-ng g−1level. Finally, we tried to extend the applicability of the method to the analysisof semivolatiles. For these studies, two natural soils contaminated with diesel fuel and wood preservative, as well asa standard urban dust contaminated with polyaromatic hydrocarbons (PAHs) were tested. Discrimination in theresponse for the heaviest compounds studied was clearly observed, due to the poor partition in the headspace and tothe slow kinetics of all the processes involved in HSSPME. © 1999 Elsevier Science B.V. All rights reserved.Keywords:Solid phase microextraction; Headspace; VOC; Soil analysis* Corresponding author. Tel./fax:+34981 547141; e-mail: qblvrlgb@usc.es0039-9140/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved.PIIS0039-9140(98)00263-X452M. Llompart et al./Talanta48 (1999) 451–4591. IntroductionA recent advance in sample preparation fortrace analysis is solid phase microextraction(SPME) technology. In this solvent-free extractiontechnique, developed in 1989 by Pawliszyn [1–5],the analytes are adsorbed directly from anaqueous [3] or gaseous phase [6] onto a fused-sil-ica fibre coated with a polymeric phase. Hencesampling, extraction and concentration are ac-complished in a single step. The entire assembly ismounted in a modified syringe needle which, afterexposure to the sampling media (water or air), isinserted into the heated injection port of a GC.The analytes are desorbed in the GC injector andanalysis of the samples is carried out. Separationand detection then proceed in the usual manner.The SPME fibre can also be suspended in theheadspace above the aqueous or solid sample(headspacesolidphasemicroextraction(HSSPME)), which eliminates interference prob-lems because the fibre is not in contact with thesample [7,8]. SPME has become very popular inthe last 2 or 3 years, especially in environmentalanalysis [9– 14].Environmental contamination with volatile or-ganic chemicals (VOCs) associated with fuel/petroleum usage is widespread in the world. Spillsduring transport and leaking storage tanks are themain sources of contamination to soils, groundwater and air. Other sources of petroleum productcontamination are heating oil tanks, refineries,aboveground tanks, terminals, pipelines, or acci-dental spills from other sources. These com-pounds have gained prominence in environmentalpollution control over the past decade as a resultof increased environmental and health concernsand the introduction of new regulations. The mostcommonly used protocols for the analysis ofVOCs in water are static headspace (HS) orpurge-and-trap techniques (PAT). These tech-niques have also been applied to the analysis ofsoils and sediments [15].In this paper we present the development of aHSSPME method to extract volatile organic com-pounds (VOCs) from soil matrices. Model VOCsinclude toluene,ortho-, meta-andpara-xylene,chlorobenzene, 1,2-, 1,3- and 1,4-dichlorobenzene.Soil samples were suspended in solvent and theSPME fibre suspended in the headspace above theslurry. Finally the fibre was desorbed in the GCinjection port and the analysis of the samples wascarried out. Different parameters affecting thedistribution of the analytes between the differentphases were investigated. The HSSPME methodat room temperature ( 20°C) was comparedwith conventional automated HS sampling at hightemperature (95°C). Due to the lack of adequatereference soil material of VOC, a typical urbansoil was spiked with a mixture of target com-pounds and aged for several months to simulatereal soil samples. Conventional HS results werecompared to the HSSPME results and found tobe in good agreement. The proposed method of-fered significant advantage in terms of linearity,precision and detection limits. Although thismethod shown to be well suited for VOC analysis,compounds of low volatility partition poorly intoHS and are generally not amenable to headspacetype of analysis. The limitation of the HSSPMEmethod developed in this work for the analysis ofsemivolatiles was studied through three naturallycontaminated samples: one with hydrocarbonsand another two with PAHs.2. Experimental2.1.InstrumentationStatic headspace analysis was performed usinga Hewlett Packard HP19395A headspace samplerand a HP5890 Series II gas chromatographequipped with a 5970 mass selective detector(MSD). Experimental parameters of the HS sam-pler were as follows: equilibration time, 30 min(nominal); bath temperature, 95°C; sample loop, 3ml; valve/loop temperature, 110°C; valve opera-tion sequence of pressurisation, 10 s; venting andfilling of loop, 5 s; and injection 15 s. The carriergas was helium at 80 ml min−1; and the auxiliarypressure of 1.5 bar. Normal HS was run using aconstant heating time accessory on the headspacesampler, consisted of a sample magazine and thecontrolling pneumatics which dropped one vial ata time into the heated carousel as the previousM. Llompart et al./Talanta48 (1999) 451–459453Fig. 1. Effect on the response after the addition of different polar solvents to the soil.sample was being analysed, such that each samplevial was equilibrated for the time equivalent toone GC run (heating up and cooling down; nomi-nally 30 min).A manual SPME holder was used with a 100-mmpolydimethylsiloxane fibre assembly (Supelco,Mississauga, ON). The analysis was performed onthe above system with the headspace transfer linedetached from the injection port. GC conditionswere the same in normal HS and in HSSPMEanalysis, and were as follows: inlet temperature,225°C; inlet mode, split operation with split ratio1:10 (splitless operation in SPME); split vent flow,60 ml min−1; oven temperature, 40°C hold 5 min,rate 7.5°C min−1to final temperature 200°C;column, 30-m SPB-1, 0.53 mm i.d., 1.5-mm film,column flow, 7.5 ml min−1nominal; linear veloc-ity, 40 cm s−1at 100°C. An open-split interfacewas used to limit the flow to the MSD to 0.7 mlmin−1. The MSD was operated in SIM mode.For PAHs analysis another GC/MSD systemsimilar to the one above was employed with a30-m DB-5 GC column (0.25 mm i.d., 0.25mmfilm). GC temperature program was: oven temper-ature, 80°C hold 1 min, rate 15°C min−1to finaltemperature 300°C. The injector temperature was260°C and the capillary interface temperature was300°C. The MSD was operated in selected ionmonitoring mode with two or three monitoredions per compound. Both systems were controlledby a HPChem station (DOS series).For total hydrocarbon analysis, a 5890 GCequipped with flame ionisation detector (FID)was used. A 30-m DB-5 GC column (0.25 mm454M. Llompart et al./Talanta48 (1999) 451–459Fig. 2. Effect on the response after the addition of different amounts of water to the soil.i.d., 0.25mmfilm) was used. Oven temperaturewas 50°C for 1 min and heated to 310°C at therate of 15°C min−1. Injector and detector temper-ature were 280 and 310°C, respectively. The GCcolumn flow was nominally 1 ml min−1.2.2.Reagents and chemicalsA ten-components VOC standard of 2000mgml−1of each of the target analytes was obtainedfrom HP (part no. 8500-6080). The target analyteswere benzene, toluene, chlorobenzene, ethylben-zene,p-, m-, o-xylene,1,2-, 1,3- and 1,4-dichlorobenzene. The standard was diluted tentimes in methanol to give a spiking solution of200mgml−1.All the solvents (analytical grade) were pur-chased from Caledon (Belleville, ON, Canada).For the study of volatiles, experiments wereperformed in a sandy-loam sub-surface soil col-lected from a garden in an urban area in Ottawa.This soil consists of 48.4% sand, 32.3% silt and13.3% clay with 2.0% organic carbon. After re-moving twigs and extraneous material it was driedin an oven at 90°C for 4 h and then homogenisedby crushing in a mortar and screened to a particlesize of 200mm.This soil did not contain any ofthe VOCs studied in this work. About 100 g wasweighed out in a jar, to which the VOC standardmixture dissolved in 100 ml of methanol wasadded to give a soil concentration of 2mgg−1ofeach of the VOC target compounds. The slurrywas allowed to stand, loosely covered to protect itfrom dust, and stirred occasionally until themethanol completely evaporated (approximately 2days). The soil was then capped and kept in adesiccator. The final VOC content of this soil wasnot known due to evaporation loss during prepa-ration and storage (approximately 18 months).Benzene has not been included in this study be-M. Llompart et al./Talanta48 (1999) 451–459455Fig. 3. Effect on the response with the headspace volume.cause due to its high volatility, it was not detectedin the aged soil. Soils spiked in this manner, andaged for a long period of time, resembled a realsample more than the common technique of spik-Table 1HSSPME detection and quantification limits for the targetVOCsDetection limit(ng g−1)TolueneChlorobenzeneEthylbenzenep+m-Xyleneo-Xylene1,3-Dichloroben-zene1,4-Dichloroben-zene1,2-Dichloroben-zene0.230.150.080.050.070.140.130.15Quantificationlimit (ng g−1)0.780.490.270.160.230.470.420.49ing one spot in the soil matrix just before analysis,because the target analytes were in more intimatecontact with the soil particles, and thus maximis-ing analyte/matrix interaction.For calibration studies a standard addition pro-tocol was used. Different levels of VOCs wereadded to the spiked soil. A 1-g soil aliquot wasadded into a 20-ml vial and spiked with a 100-mlof MeOH containing the VOCs. After capping,the vials were tumbled for 0.5 h and allowed toequilibrate at room temperature for 24 h beforesampling and analysis.For the analysis of semivolatiles three real sam-ples were used: (i) a soil contaminated with dieselfuel from a gas process plant, in which weanalysed the total hydrocarbon content; (ii) awood preservative contaminated soil (SRS103-100) purchased from Fisher Scientific (Fair Lawn,NJ) for the analysis of PAHs; and (iii) an urbandust (SRM 1649) purchased from NIST(Gaithersburg, MD) for the analysis of PAHs. [ Pobierz całość w formacie PDF ]
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//-->Talanta 48 (1999) 451– 459Headspace solid phase microextraction (HSSPME) for thedetermination of volatile and semivolatile pollutants in soilsMaria Llomparta,*, Ken Lib, Merv FingasbDepartamento de Quimica Analitica Nutricion y Bromatologia, Facultad de Quimica, Uni6ersidad de Santiago de Compostela,E-15706Santiago de Compostela, SpainbEmergencies Science Di6ision, En6ironment Canada, En6ironmental Technology Centre,3439Ri6er Road, Ottawa, ON, CanadaReceived 3 April 1998; received in revised form 10 July 1998; accepted 3 August 1998aAbstractWe have investigated the use of headspace solid phase microextraction (HSSPME) as a sample concentration andpreparation technique for the analysis of volatile and semivolatile pollutants in soil samples. Soil samples weresuspended in solvent and the SPME fibre suspended in the headspace above the slurry. Finally, the fibre was desorbedin the Gas Chromatograph (GC) injection port and the analysis of the samples was carried out. Since the transfer ofcontaminants from the soil to the SPME fibre involves four separate phases (soil-solvent-headspace and fibre coating),parameters affecting the distribution of the analytes were investigated. Using a well-aged artificially spiked gardensoil, different solvents (both organic and aqueous) were used to enhance the release of the contaminants from thesolid matrix to the headspace. It was found that simple addition of water is adequate for the purpose of analysingthe target volatile organic chemicals (VOCs) in soil. The addition of 1 ml of water to 1 g of soil yielded maximumresponse. Without water addition, the target VOCs were almost not released from the matrix and a poor response wasobserved. The effect of headspace volume on response as well as the addition of salt were also investigated.Comparison studies between conventional static headspace (HS) at high temperature (95°C) and the new technologyHSSPME at room temperature ( 20°C) were performed. The results obtained with both techniques were in goodagreement. HSSPME precision and linearity were found to be better than automated headspace method andHSSPME also produced a significant enhancement in response. The detection and quantification limits for the targetVOCs in soils were in the sub-ng g−1level. Finally, we tried to extend the applicability of the method to the analysisof semivolatiles. For these studies, two natural soils contaminated with diesel fuel and wood preservative, as well asa standard urban dust contaminated with polyaromatic hydrocarbons (PAHs) were tested. Discrimination in theresponse for the heaviest compounds studied was clearly observed, due to the poor partition in the headspace and tothe slow kinetics of all the processes involved in HSSPME. © 1999 Elsevier Science B.V. All rights reserved.Keywords:Solid phase microextraction; Headspace; VOC; Soil analysis* Corresponding author. Tel./fax:+34981 547141; e-mail: qblvrlgb@usc.es0039-9140/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved.PIIS0039-9140(98)00263-X452M. Llompart et al./Talanta48 (1999) 451–4591. IntroductionA recent advance in sample preparation fortrace analysis is solid phase microextraction(SPME) technology. In this solvent-free extractiontechnique, developed in 1989 by Pawliszyn [1–5],the analytes are adsorbed directly from anaqueous [3] or gaseous phase [6] onto a fused-sil-ica fibre coated with a polymeric phase. Hencesampling, extraction and concentration are ac-complished in a single step. The entire assembly ismounted in a modified syringe needle which, afterexposure to the sampling media (water or air), isinserted into the heated injection port of a GC.The analytes are desorbed in the GC injector andanalysis of the samples is carried out. Separationand detection then proceed in the usual manner.The SPME fibre can also be suspended in theheadspace above the aqueous or solid sample(headspacesolidphasemicroextraction(HSSPME)), which eliminates interference prob-lems because the fibre is not in contact with thesample [7,8]. SPME has become very popular inthe last 2 or 3 years, especially in environmentalanalysis [9– 14].Environmental contamination with volatile or-ganic chemicals (VOCs) associated with fuel/petroleum usage is widespread in the world. Spillsduring transport and leaking storage tanks are themain sources of contamination to soils, groundwater and air. Other sources of petroleum productcontamination are heating oil tanks, refineries,aboveground tanks, terminals, pipelines, or acci-dental spills from other sources. These com-pounds have gained prominence in environmentalpollution control over the past decade as a resultof increased environmental and health concernsand the introduction of new regulations. The mostcommonly used protocols for the analysis ofVOCs in water are static headspace (HS) orpurge-and-trap techniques (PAT). These tech-niques have also been applied to the analysis ofsoils and sediments [15].In this paper we present the development of aHSSPME method to extract volatile organic com-pounds (VOCs) from soil matrices. Model VOCsinclude toluene,ortho-, meta-andpara-xylene,chlorobenzene, 1,2-, 1,3- and 1,4-dichlorobenzene.Soil samples were suspended in solvent and theSPME fibre suspended in the headspace above theslurry. Finally the fibre was desorbed in the GCinjection port and the analysis of the samples wascarried out. Different parameters affecting thedistribution of the analytes between the differentphases were investigated. The HSSPME methodat room temperature ( 20°C) was comparedwith conventional automated HS sampling at hightemperature (95°C). Due to the lack of adequatereference soil material of VOC, a typical urbansoil was spiked with a mixture of target com-pounds and aged for several months to simulatereal soil samples. Conventional HS results werecompared to the HSSPME results and found tobe in good agreement. The proposed method of-fered significant advantage in terms of linearity,precision and detection limits. Although thismethod shown to be well suited for VOC analysis,compounds of low volatility partition poorly intoHS and are generally not amenable to headspacetype of analysis. The limitation of the HSSPMEmethod developed in this work for the analysis ofsemivolatiles was studied through three naturallycontaminated samples: one with hydrocarbonsand another two with PAHs.2. Experimental2.1.InstrumentationStatic headspace analysis was performed usinga Hewlett Packard HP19395A headspace samplerand a HP5890 Series II gas chromatographequipped with a 5970 mass selective detector(MSD). Experimental parameters of the HS sam-pler were as follows: equilibration time, 30 min(nominal); bath temperature, 95°C; sample loop, 3ml; valve/loop temperature, 110°C; valve opera-tion sequence of pressurisation, 10 s; venting andfilling of loop, 5 s; and injection 15 s. The carriergas was helium at 80 ml min−1; and the auxiliarypressure of 1.5 bar. Normal HS was run using aconstant heating time accessory on the headspacesampler, consisted of a sample magazine and thecontrolling pneumatics which dropped one vial ata time into the heated carousel as the previousM. Llompart et al./Talanta48 (1999) 451–459453Fig. 1. Effect on the response after the addition of different polar solvents to the soil.sample was being analysed, such that each samplevial was equilibrated for the time equivalent toone GC run (heating up and cooling down; nomi-nally 30 min).A manual SPME holder was used with a 100-mmpolydimethylsiloxane fibre assembly (Supelco,Mississauga, ON). The analysis was performed onthe above system with the headspace transfer linedetached from the injection port. GC conditionswere the same in normal HS and in HSSPMEanalysis, and were as follows: inlet temperature,225°C; inlet mode, split operation with split ratio1:10 (splitless operation in SPME); split vent flow,60 ml min−1; oven temperature, 40°C hold 5 min,rate 7.5°C min−1to final temperature 200°C;column, 30-m SPB-1, 0.53 mm i.d., 1.5-mm film,column flow, 7.5 ml min−1nominal; linear veloc-ity, 40 cm s−1at 100°C. An open-split interfacewas used to limit the flow to the MSD to 0.7 mlmin−1. The MSD was operated in SIM mode.For PAHs analysis another GC/MSD systemsimilar to the one above was employed with a30-m DB-5 GC column (0.25 mm i.d., 0.25mmfilm). GC temperature program was: oven temper-ature, 80°C hold 1 min, rate 15°C min−1to finaltemperature 300°C. The injector temperature was260°C and the capillary interface temperature was300°C. The MSD was operated in selected ionmonitoring mode with two or three monitoredions per compound. Both systems were controlledby a HPChem station (DOS series).For total hydrocarbon analysis, a 5890 GCequipped with flame ionisation detector (FID)was used. A 30-m DB-5 GC column (0.25 mm454M. Llompart et al./Talanta48 (1999) 451–459Fig. 2. Effect on the response after the addition of different amounts of water to the soil.i.d., 0.25mmfilm) was used. Oven temperaturewas 50°C for 1 min and heated to 310°C at therate of 15°C min−1. Injector and detector temper-ature were 280 and 310°C, respectively. The GCcolumn flow was nominally 1 ml min−1.2.2.Reagents and chemicalsA ten-components VOC standard of 2000mgml−1of each of the target analytes was obtainedfrom HP (part no. 8500-6080). The target analyteswere benzene, toluene, chlorobenzene, ethylben-zene,p-, m-, o-xylene,1,2-, 1,3- and 1,4-dichlorobenzene. The standard was diluted tentimes in methanol to give a spiking solution of200mgml−1.All the solvents (analytical grade) were pur-chased from Caledon (Belleville, ON, Canada).For the study of volatiles, experiments wereperformed in a sandy-loam sub-surface soil col-lected from a garden in an urban area in Ottawa.This soil consists of 48.4% sand, 32.3% silt and13.3% clay with 2.0% organic carbon. After re-moving twigs and extraneous material it was driedin an oven at 90°C for 4 h and then homogenisedby crushing in a mortar and screened to a particlesize of 200mm.This soil did not contain any ofthe VOCs studied in this work. About 100 g wasweighed out in a jar, to which the VOC standardmixture dissolved in 100 ml of methanol wasadded to give a soil concentration of 2mgg−1ofeach of the VOC target compounds. The slurrywas allowed to stand, loosely covered to protect itfrom dust, and stirred occasionally until themethanol completely evaporated (approximately 2days). The soil was then capped and kept in adesiccator. The final VOC content of this soil wasnot known due to evaporation loss during prepa-ration and storage (approximately 18 months).Benzene has not been included in this study be-M. Llompart et al./Talanta48 (1999) 451–459455Fig. 3. Effect on the response with the headspace volume.cause due to its high volatility, it was not detectedin the aged soil. Soils spiked in this manner, andaged for a long period of time, resembled a realsample more than the common technique of spik-Table 1HSSPME detection and quantification limits for the targetVOCsDetection limit(ng g−1)TolueneChlorobenzeneEthylbenzenep+m-Xyleneo-Xylene1,3-Dichloroben-zene1,4-Dichloroben-zene1,2-Dichloroben-zene0.230.150.080.050.070.140.130.15Quantificationlimit (ng g−1)0.780.490.270.160.230.470.420.49ing one spot in the soil matrix just before analysis,because the target analytes were in more intimatecontact with the soil particles, and thus maximis-ing analyte/matrix interaction.For calibration studies a standard addition pro-tocol was used. Different levels of VOCs wereadded to the spiked soil. A 1-g soil aliquot wasadded into a 20-ml vial and spiked with a 100-mlof MeOH containing the VOCs. After capping,the vials were tumbled for 0.5 h and allowed toequilibrate at room temperature for 24 h beforesampling and analysis.For the analysis of semivolatiles three real sam-ples were used: (i) a soil contaminated with dieselfuel from a gas process plant, in which weanalysed the total hydrocarbon content; (ii) awood preservative contaminated soil (SRS103-100) purchased from Fisher Scientific (Fair Lawn,NJ) for the analysis of PAHs; and (iii) an urbandust (SRM 1649) purchased from NIST(Gaithersburg, MD) for the analysis of PAHs. [ Pobierz całość w formacie PDF ]