Determination of organochlorine pesticides by gas chromatography with solid-phase microextraction

Summary A study of different extraction techniques for the determination of a selected group of organochlorine compounds in surface waters is presented. Comparison of liquid-liquid extraction (LLE) with solid-phase extraction (SPE) and solid-phase microextraction (SPME) with fibers of different polarity shows that SPME with a recently commercialised fiber of polydimethylsiloxane divinylbenzene allows these compounds to be determined in surface waters with good extraction efficiencies. Extraction time, effect of temperature, ionic strength and pH were optimised, allowing quantification in agricultural effluents in the range 1.0–60 ng·L⁻¹.     

Determination of organochlorine pesticides in ground water samples using solid-phase microextraction by gas chromatography-electron capture detection

A direct immersion solid-phase microextraction coupled with gas chromatography-electron capture detection (SPME-GC-ECD) method was optimized and validated for the quantitative determination of 18 organochlorine pesticides in ground water. Ionic strength, stirring speed, adsorption and desorption time and pH were some of the parameters investigated in order to select the optimum conditions for SPME with a 50/30 DVB/CAR/PDMS fiber coating. The SPME-GC/ECD method showed good linear response below 10 ng L⁻¹ with R² values in the range of 0.9950–0.9997. The repeatability of the measurements were lower than 10%. Values of relative recoveries located within the acceptable range (80–120%). Limits of quantification (LOQ) from 4.5 × 10⁻³ to 1.5 ng L⁻¹ were obtained. On average 8 organochlorines were found per sample, even so all the 18 organochlorines were quantified among them. Substances such as endrin ketone, γ-BHC and β-BHC were the pesticides determined in larger concentration (0.06–305 ng L⁻¹), while methoxychlor and aldrin in smaller amounts (0.151–1.55 ng L⁻¹). Measured levels of organochlorine pesticides were above the limits established by Brazilian regulations.     

Applicability of headspace solid-phase microextraction to the determination of multi-class pesticides in waters

The applicability of headspace solid-phase microextraction (HS-SPME) to pesticide determination in water samples was demonstrated by evaluating the effects of temperature on the extraction of the pesticides. The evaluations were performed using an automated system with a heating module. The 174 pesticides that are detectable with gas chromatograph were selected objectively and impartially based on their physical properties: vapor pressure and partition coefficient between octanol and water. Of the 174 pesticides, 158 (90% of tested) were extracted with a polyacrylate-coated fiber between 30 and 100 degrees C and were determined with gas chromatograph-mass spectrometry. The extraction-temperature profiles of the 158 extracted pesticides were obtained to evaluate the effects of temperature on the extraction of pesticides. The pesticides were classified into four groups according to the shape of their extraction-temperature profiles. The line of demarcation between extractable pesticides and non-extractable pesticides could be drawn in the physical property diagram (a double logarithmic plot of their vapor pressure and partition coefficient between octanol and water). The plot also revealed relationships between classified extraction features and their physical properties. The new method for multi residue screening in which the analytes were categorized into sub-groups based on extraction temperature was developed. In order to evaluate the quantitivity of the developed method, the 45 pesticides were chosen among the pesticides that are typically monitored in waters. Linear response data for 40 of the 45 was obtained in the concentration range below 5 microg/l with correlation coefficients ranging between 0.979 and 0.999. The other five pesticides had poor responses. Relative standard deviations at the concentration of the lowest standard solution for each calibration curve of the pesticides ranged from 3.6 to 18%. The value of 0.01 microg/l in the limits of detection for 17 pesticides was achieved only under the approximate conditions for screening, not under the individually optimized conditions for each pesticide. Recoveries of tested pesticides in actual matrices were essentially in agreement with those obtained by solid-phase extraction.     

A novel graphene nanosheets coated stainless steel fiber for microwave assisted headspace solid phase microextraction of organochlorine pesticides in aqueous samples followed by gas chromatography with electron capture detection

In this study, a novel graphene nanosheets (GNSs) coated solid phase microextraction (SPME) fiber was prepared by immobilizing microwave synthesized GNSs on a stainless steel wire. Microwave synthesized GNSs were verified by X-ray diffraction, field emission-scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM). GNS-SPME fiber was characterized using FE-SEM and the results showed the GNS coating was homogeneous, porous, and highly adherent to the surface of the stainless steel fiber. The performance and feasibility of the GNS-SPME fiber was evaluated under one-step microwave assisted (MA) headspace (HS) SPME followed by gas chromatography with electron capture detection for five organochlorine pesticides (OCPs) in aqueous samples. Parameters influencing the extraction efficiency of MA-HS-GNS-SPME such as microwave irradiation power and time, pH, ionic strength, and desorption conditions were thoroughly examined. Under the optimized conditions, detection limits for the OCPs varied between 0.16 and 0.93 ng L(-1) and linear ranges varied between 1 and 1500 n gL(-1), with correlation coefficients ranging from 0.9984 to 0.9998, and RSDs in the range of 3.6-15.8% (n=5). In comparison with the commercial 100 μm polydimethylsiloxane fiber, the GNS coated fiber showed better extraction efficiency, higher mechanical and thermal stability (up to 290°C), longer life span (over 250 times), and lower production cost. The method was successfully applied to the analysis of real water samples with recoveries ranged between 80.1 and 101.1% for river water samples. The results demonstrated that the developed MA-HS-GNS-SPME method was a simple, rapid, efficient pretreatment and environmentally friendly procedure for the analysis of OCPs in aqueous samples.     

Determination of pyrethroid,organophosphate and organochlorine pesticides in water by headspace solid-phase microextraction

Simultaneous determination of pyrethroid, organophosphate (OP) and organochlorine (OC) pesticides in water was achieved with headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-electron-capture detection (GC-ECD). The parameters affecting HS-SPME of pesticides from water were optimized, including extraction temperature, sample and headspace volumes, and sodium chloride amounts. The effects of desorption temperature, desorption time, and position of the fibre in the GC inlet were also investigated. Extraction temperature was the most important factor affecting the recoveries of analytes, and the optimized temperature was 96°C. The addition of salt did not increase extraction efficiencies of the pesticides from the water. The optimized desorption conditions in the GC were as follows: desorption time of 10?min; desorption temperature of 260°C; and a 2?cm position of the fibre in the inlet. The method detection limits were in the low-ng/L level with a linearity range of 50–1000?ng/L for the OCs, 50–5000?ng/L for the OP, and 50–20?000?ng/L for the pyrethroids. These data demonstrated that HS-SPME is a sensitive method for the determination of pyrethroid, OC, and OP pesticides in water.     

Analysis of aqueous pyrethroid residuals by one-step microwave-assisted headspace solid-phase microextraction and gas chromatography with electron capture detection

A one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) has been applied to be a pretreatment step in the analysis of aqueous pyrethroid residuals by gas chromatography (GC) with electron capture detection (ECD). Microwave heating was applied to accelerate the vaporization of pyrethroids (bioallenthrin, bifenthrin, fenpropathrin, cyhalothrin, permethrin, cyfluthrin, cypermethrin, fluvalinate, fenvalerate and deltamethrin) into the headspace, and then being absorbed directly on a SPME fiber under the controlled conditions. Optimal conditions for the SPME sampling, such as the selection of sampling fiber, sample pH, sampling temperature and time, microwave irradiation power, desorption temperature and time were investigated and then applied to real sample analysis. Experimental results indicated that the extraction of pyrethroids from a 20-mL aquatic sample (pH 4.0) was achieved with the best efficiency through the use of a 100-μm PDMS fiber, microwave irradiation of 157 W and sampling at 30 °C for 10 min. Under optimum conditions, the detections were linear in the range of 0.05-0.5 μg/L with the square of correlation coefficients (R²) of >0.9913 for pyrethroids except bifenthrin being 0.9812. Method detection limits (MDL) were found to be varied from 0.2 to 2.6 ng/L for different pyrethroids based on S/N (signal to noise) = 3. The coefficients of variation (CVs) for repeatability were 7-21%. A field underground water sample was analyzed with recovery between 88.5% to 115.5%. This method was proven to be a very simple, rapid, and solvent-free process to achieve the sample pretreatment before the analysis of trace pyrethroids in aqueous samples by gas chromatography.     

Determination of fuel dialkyl ethers and BTEX in water using headspace solid-phase microextraction and gas chromatography-flame ionization detection

A simple procedure for the determination of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), ethyl butyl ether (EBE), tert-amyl methyl ether (TAME), benzene, toluene, ethylbenzene, and xylenes (BTEX) in water using headspace (HS) solid-phase microextraction (HS-SPME) was developed. The analysis was carried out by gas chromatography (GC) equipped with flame ionization detector (FID) and 100% dimethylpolysiloxane fused capillary column. A 2 Plackett-Burman design for screening and a central composite design (CCD) for optimizing the significant variables were applied. Fiber type, extraction temperature, sodium chloride concentration, and headspace volume were the significant variables. A 65 microm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 10 degrees C, 300 g/l, and 20 ml of headspace (in 40 ml vial) were respectively chosen for the best extraction response. An extraction time of 10 min was enough to extract the ethers and BTEX. The relative standard deviation (R.S.D.) for the procedure varied from 2.6 (benzene) to 8.5% (ethylbenzene). The method detection limits (MDLs) found were from 0.02 (toluene, ethylbenzene, and xylenes) to 1.1 microg/l (MTBE). The optimized method was applied to the analysis of the rivers, marinas and fishing harbors surface waters from Gipuzkoa (North Spain). Three sampling were done in 1 year from June 2002 to June 2003. Toluene was the most detected analyte (in 90% of the samples analyzed), with an average concentration of 0.56 microg/l. MTBE was the only dialkyl ether detected (in 15% of the samples) showing two high levels over 400 microg/l that were related to accidental fuel spill.     

Determination of organochlorine pesticides and their metabolites in radish after headspace solid-phase microextraction using calix[4]arene fiber

A novel laboratory-made sol-gel calix[4]arene/hydroxy-terminated silicone oil coated fiber has been applied for headspace solid-phase microextraction (HS-SPME) combined with gas chromatography (GC) with electron capture detection (ECD) to determine 12 organochlorine pesticides (OCPs) and their metabolites in radish sample. The analytes in the study consisted of α-, β-, γ- and δ-hexachlorocyclohexane (BHC), 1,1,1-trichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethane (o,p′-DDT), 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p′-DDT), 2,4-dichlorobenzophenone (o,p′-DBP), 4,4-dichlorobenzophenone (p,p′-DBP), 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (p,p′-DDE), bis(4-chlorophenyl)methane (p,p′-DDM), 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (p,p′-DDD) and endrin. The following parameters were adjusted to optimize HS-SPME in order to obtain the maximum sensitivity: extraction temperature, extraction time, the addition of salt, desorption temperature and time. Especially, the effect of the complex radish matrix on quantitative extraction of pesticides was discussed in detail. Detection limits of the developed method for radish matrices were below 174 ng/kg for all pesticides. Relative standard deviations for quintuplicate analyses of radish samples fortified each analytes were not higher than 13.1%. The results demonstrate the suitability of the HS-SPME/GC-ECD approach for the analysis of multi-residue OCPs and metabolites in radish.     

Analysis of polychlorinated biphenyls in aqueous samples by microwave-assisted headspace solid-phase microextraction

The hyphenated technique namely microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) was developed and studied for the simultaneous extraction/enrichment of polychlorinated biphenyls (PCBs) in aqueous samples prior to the quantification by gas chromatography (GC). The PCBs in aqueous media are extracted onto a solid-phase micro fibre via the headspace with the aid of microwave irradiation. The optimum conditions for obtaining extraction efficiency, such as the extraction time, addition of salts, addition of methanol, ratio of sample to headspace volume, and the desorption parameters were investigated. Experimental results indicated that the proposed MA-HS-SPME method attained the best extraction efficiency under the optimized conditions, i.e., irradiation of extraction solution (20 ml aqueous sample in 40 ml headspace vial with no additions of salt and methanol) under 30 W microwave power for 15 cycles (1 min power on and 3 min power off of each cycle). Desorption at 270 degrees C for 3 min provided the best detection results. The detection limit obtained were between 0.27 and 1.34 ng/l. The correlation coefficient for the linear dynamic range from 1 to 80 ng/l exceeded 0.99 for 18 PCBs.     

Development and application of polymer-coated hollow fiber membrane microextraction to the determination of organochlorine pesticides in water

A novel extraction procedure coupled with gas chromatography-mass spectrometric detection for quantification of organochlorine pesticides (OCPs) in water is described. Amphiphilic polyhydroxylated polyparaphenylene (PH-PPP) was synthesized and coated on the surfaces of a porous polypropylene hollow fiber membrane (HFM). Due to the high porosity of the HFM, maximum active surface area to achieve high extraction efficiency is expected. The polymer-coated HFM was used for the extraction of 15 OCPs from water. The extraction efficiency was compared with emerging and established methods such as liquid-phase microextraction (LPME), solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE) techniques. We term the current procedure as polymer-coated hollow fiber microextraction (PC-HFME). PC-HFME showed good selectivity and sensitivity. Detection limits for OCPs were in the range of 0.001-0.008 microg l(-1). The sensitivity and selectivity of the coated HFM could be adjusted by changing the characteristics of the coated PH-PPP film.     

On-line determination of organochlorine pesticides in water by solid-phase microextraction and gas chromatography with electron capture detection

This paper describes the extraction of 20 organochlorine pesticides (OCPs) from water samples using solid-phase microextraction (SPME). Three fused-silica fibers coated or bonded with polydimethylsiloxane (PDMS) of different film thicknesses (20-, 30-, and 100-μm) were evaluated. The extraction time, the effects of stirring and addition of NaCl to the aqueous sample, the linear range and the precision of this technique, and the effect of carryover were examined for 20 analytes and are presented here. A comparison with results using conventional liquid-liquid extraction demonstrate that the SPME technique is well suited as a fast screening technique for OCPs in water samples.     

Determination of organochlorine pesticides in water using dynamic hook-type liquid-phase microextraction

We developed a simple and efficient headspace liquid-phase microextraction (LPME) technique named dynamic hook-type liquid-phase microextraction (DHT-LPME) and used it in combination with gas chromatography-mass spectrometry (GC-MS) and an electron capture detector (ECD). Aqueous specimens of organochlorine pesticides (OCPs) were used as model compounds to demonstrate the effectiveness of the technique. In the present study, the calibration curves were linear over at least 2 orders of magnitude with R² values of 0.997. The method detection limits (MDLs) varied from 2 to 44.0 ng L⁻¹. The precision of DHT-LPME ranged from 6.5 to 14.4%. The relative recoveries of OCPs in rainwater were more than 84.2%. Enrichment factors (EF) in the range 275-1127 were obtained using DHT-LPME.     

Preparation of C18 composite solid-phase microextraction fiber and its application to the determination of organochlorine pesticides in water samples

In this work, a C18 composite solid-phase microextraction (SPME) fiber was prepared with a new method and applied to the analysis of organochlorine pesticides (OCPs) in water sample. A stainless steel wire (o.d. 127 μm) was used as the substrate, and a mixture of the C18 particle (3.5 μm) and the 184 silicone was used as the coating material. During the process of fiber preparation, a section of capillary column was used to fix the mixture onto the stainless steel wire and to ensure the constant of coating thickness. The prepared fiber showed excellent thermal stability and solvent resistance. By coupling with gas chromatography–mass spectrometry (GC–MS), the fiber exhibited wide linearity (2–500 ng L⁻¹) and good sensitivity for the determination of six OCPs in water samples, the OCPs tested included hexachlorobezene, trans-chlordane, cis-chlordane, o,p-DDT, p,p-DDT and mirex. Not only the extraction performance of the newly prepared fiber was more than seven times higher than those of commercial fibers, the limits of detections (LODs) (0.059–0.151 ng L⁻¹) for OCPs achieved under optimized conditions were also lower than those of reported SPME methods. The fiber was successfully applied to the determination of OCPs in real water samples by using developed SPME–GC–MS method.     

Comparison of pressurized liquid extraction and microwave assisted extraction for the determination of organochlorine pesticides in vegetables

A method to determine organochlorine pesticides in horticultural samples (lettuce, tomato, spinach, potato, turnip leaf and green bean) using pressurized liquid extraction (PLE) is described and compared with microwave assisted extraction (MAE). Significant parameters affecting PLE procedure such as temperature, static extraction time and extraction solvent were optimised and discussed. Clean-up of extracts was performed by solid phase extraction (SPE) using a carbon cartridge as adsorbent. Pesticides were determined by gas chromatography and electron capture detection (GC-ECD). Analytical recoveries obtained were ca. 100% and the relative standard deviations were lower than 15% for most of the studied pesticides with the proposed methods in each analysed matrix.     

Optimisation of solid-phase microextraction coupled to HPLC-UV for the determination of organochlorine pesticides and their metabolites in environmental liquid samples

A solid-phase microextraction (SPME) procedure using two commercial fibers coupled with high-performance liquid chromatography (HPLC) is presented for the extraction and determination of organochlorine pesticides in water samples. We have evaluated the extraction efficiency of this kind of compound using two different fibers: 60-μm polydimethylsiloxane–divinylbenzene (PDMS-DVB) and Carbowax/TPR-100 (CW/TPR). Parameters involved in the extraction and desorption procedures (e.g. extraction time, ionic strength, extraction temperature, desorption and soaking time) were studied and optimized to achieve the maximum efficiency. Results indicate that both PDMS-DVB and CW/TPR fibers are suitable for the extraction of this type of compound, and a simple calibration curve method based on simple aqueous standards can be used. All the correlation coefficients were better than 0.9950, and the RSDs ranged from 7% to 13% for 60-μm PDMS-DVB fiber and from 3% to 10% for CW/TPR fiber. Optimized procedures were applied to the determination of a mixture of six organochlorine pesticides in environmental liquid samples (sea, sewage and ground waters), employing HPLC with UV-diode array detector.     

Determination of aromatic hydrocarbons in asphalt release agents using headspace solid-phase microextraction and gas chromatography-mass spectrometry

The possibility of quantitative analysis of aromatic hydrocarbons in oil-based asphalt release agents was investigated using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS). The target analytes studied were benzene, toluene, ethylbenzene, p-, m-, and o-xylene (BTEX) and 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene. Experimental parameters influencing HS-SPME efficiency were studied (equilibration time between sample and headspace and between headspace and SPME fiber, sample amount and sample matrice effects). A HS-SPME method using hexadecane as a surrogate matrice was developed. The detection limit was estimated as 0.03-0.08 ppm (w/w) for the target analytes investigated. Good linearity was observed (R2 > 0.999) for all calibration curves at high, medium and low concentration level. The repeatability of the method (RSD, relative standard deviation) was found to be less than 10% (generally less than 5%) in triplicate samples and approximately 2% at eight consecutive tests on one and the same sample. The accuracy of the method given by recovery of spiked samples was between 85 and 106% (generally between 95 and 105%). The HS-SPME method developed was applied to four commercially available asphalt release agents. External calibration and standard addition approaches were investigated regarding accuracy. The results showed that standard addition generates higher accuracy than external calibration. The contents of target aromatic hydrocarbons in the asphalt release agents studied varied greatly from approximately 0.1-700 ppm. The method described looks promising, and could be a valuable tool for determination of aromatic hydrocarbons in different types of organic matrices.     

A new porous-layer activated-charcoal-coated fused silica fiber: Application for determination of BTEX compounds in water samples using headspace solid-phase microextraction and capillary gas chromatography

Summary Extra-fine powdered activated charcoal has been used as stationary phase (coating layer) in solid-phase microextraction (SPME). The efficiency and reliability of the prepared device have been investigated for the extraction of some volatile organic compounds such as benzene, toluene, ethylbenzene and xylene isomers (BTEX) from the headspace of water samples. Monitoring of the extracted compounds and further quantitative analysis of the real samples have been performed by capillary GC-FID. Effects of several factors such as temperature, addition of salt, and stirring speed on extraction efficiency and exposure time have been studied. Under optimum conditions, extraction recoveries for these compounds from 50 mL water were >95%. The calibration graphs were linear in the range 5 to 10⁴ pg mL⁻¹ and the detection limit for each BTEX compound was 1.5–2 pg mL⁻¹. The results obtained by use of this porous layer activated charcoal (PLAC)-coated fiber have also been compared with results reported in the literature by use of a polydimethylsiloxane (PDMS)-coated fiber. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Determination of organochlorine pesticides in water samples by dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry

A rapid and simple dispersive liquid-liquid microextraction (DLLME) has been developed to preconcentrate eighteen organochlorine pesticides (OCPs) from water samples prior to analysis by gas chromatography-mass spectrometry (GC-MS). The studied variables were extraction solvent type and volume, disperser solvent type and volume, aqueous sample volume and temperature. The optimum experimental conditions of the proposed DLLME method were: a mixture of 10 μL tetrachloroethylene (extraction solvent) and 1 mL acetone (disperser solvent) exposed for 30 s to 10 mL of the aqueous sample at room temperature (20 °C). Centrifugation of cloudy solution was carried out at 2300 rpm for 3 min to allow phases separation. Finally, 2 μL of extractant was recovered and injected into the GC-MS instrument. Under the optimum conditions, the enrichment factors ranged between 46 and 316. The calculated calibration curves gave a high-level linearity for all target analytes with correlation coefficients ranging between 0.9967 and 0.9999. The repeatability of the proposed method, expressed as relative standard deviation, varied between 5% and 15% (n = 8), and the detection limits were in the range of 1-25 ng L⁻¹. The LOD values obtained are able to detect these OCPs in aqueous matrices as required by EPA methods 525.2 and 625. Analysis of spiked real water samples revealed that the matrix had no effect on extraction for river, surface and tap waters; however, urban wastewater sample shown a little effect for five out of eighteen analytes.     

On-line determination of organophosphorus pesticides in water by solid-phase microextraction and gas chromatography with thermionic-selective detection

This paper describes the extraction of 49 organophosphorus pesti-cides (OPPs) from water samples using solid-phase microextraction (SPME). Three fibers, including a 15-μm XAD-coated fiber, a 85-μm polyacrylate-coated fiber, and a 30-μm polydimethylsilox-ane-coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate-coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD- and polyacrylate-coated fibers. With some exceptions, the XAD- and polyacrylate-coated fibers performed better than the PDMS-coated fiber. The superiority of the XAD-nd polyacrylate-coated fiber. The superiority of the XAD- and polyacrylate-coated fibers over the PDMS-coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber.     

Determination of aliphatic amines in water by gas chromatography using headspace solvent microextraction

The possibility of applying headspace microextraction into a single drop for the determination of amines in aqueous solutions is demonstrated. A 1 μl drop of benzyl alcohol containing 2-butanone as an internal standard was suspended from the tip of a micro syringe needle over the headspace of stirred sample solutions for extraction. The drop was then injected directly into a GC. The total chromatographic determination was less than 10 min. Optimization of experimental conditions (sampling time, sampling temperature, stirring rate, ionic strength of the solution, concentration of reagents, time of extraction and organic drop volume) with respect to the extraction efficiency were investigated and the linear range and the precision were also examined. Calibration curves yielded good linearity and concentrations down to 2.5 ng ml⁻¹ were detectable with R.S.D. values ranging from 6.0 to 12.0%. Finally, the method was successfully applied to the extraction and determination of amines in tap and river water samples. This system represents an inexpensive, fast, simple and precise sample cleanup and preconcentration method for the determination of volatile organic compounds at trace levels.