Determination of benzene, toluene, ethylbenzene and xylenes in soils by multiple headspace solid-phase microextraction

Multiple headspace-solid phase microextraction (MHS-SPME) is a recently developed technique for the quantification of analytes in solid samples that avoids the matrix effect. This method implies several consecutive extractions from the same sample. In this way, the total area corresponding to complete extraction can be directly calculated as the sum of the areas of each individual extraction when the extraction is exhaustive, or through a mathematical equation when it is not exhaustive. In this paper, the quantitative determination of benzene, toluene, ethylbenzene and xylene isomers (BTEX) in a certified soil (RTC-CRM304, LGC Promochem) and in a contaminated soil by multiple HS-SPME coupled to a gas chromatography-flame ionisation detector (GC-FID) is presented. BTEX extraction was carried out using soil suspensions in water at 30 degrees C with a 75 microm carboxen-polydimethylsiloxane (CAR-PDMS) fibre and calibration was carried out using aqueous BTEX solutions at 30 degrees C for 30 min with the same fibre. BTEX concentration was calculated by interpolating the total peak area found for the soils in the calibration graphs obtained from aqueous solutions. The toluene, ethylbenzene, o-xylene and m,p-xylene concentrations obtained were statistically equal to the certified values.     

A new disposable ionic liquid based coating for headspace solid-phase microextraction of methyl tert-butyl ether in a gasoline sample followed by gas chromatography-flame ionization detection

A new ionic liquid (IL) based solid-phase microextraction (SPME) fiber was investigated and used for headspace (HS) extraction of methyl tert-butyl ether (MTBE) in a gasoline sample. Using the new IL coated HS-SPME fiber with the combination of gas chromatography-flame ionization detection (GC-FID); sub-to-low μg L⁻¹ concentrations of MTBE were detected. Four different ILs including 1-butyl-3-methylimidazolium tetraflouroborate ([C₄C₁IM] [BF₄]), 1-octyl-3-methylimidazolium tetraflouroborate ([C₈C₁IM] [BF₄]), 1-octyl-3-methylimidazolium hexaflourophosphate ([C₈C₁IM] [PF₆]) and 1-ethyl-3-methylimidazolium ethylsulphate ([C₂C₁IM] [ETSO₄]) were synthesized and examined for extraction, preconcentration and determination of MTBE. It was observed that [C₈C₁IM] [BF₄] showed the highest extraction efficiency and possessed the best extractability for MTBE. The fiber coating takes up the compounds from the sample by absorption in the case of liquid coatings. The calibration graph was linear in a concentration range of 1-120 μg L⁻¹ (R² > 0.994) with the detection limit of 0.09 μg L⁻¹ level. The new IL-coated fiber was applied successfully for the determination of MTBE in a gasoline sample with good recoveries between 90 and 95%.     

Electrodeposition of a copolymer nanocomposite for the headspace solid-phase microextraction of benzene,toluene, ethylbenzene and xylenes

In this study, polyaniline-co-poly(o-toluidine)/graphene oxide nanosheets composite was electrodeposited on the surface of a stainless steel wire as a new coating for headspace solid-phase microextraction of benzene, toluene, ethylbenzene and xylenes (BTEX) with gas chromatography–mass spectrometry. The characteristics of the new coating were evaluated by the scanning electron microscopy and Fourier transform infrared spectroscopy. To study the coating performance, the influence of various parameters such as deposition potential and time, concentration of the monomers and GONSs, desorption temperature and time, extraction temperature and time and ionic strength on BTEX extraction efficiency was investigated. At the optimum conditions, the linear ranges and detection limits (S/N?=?3) were found 0.01–50 and 0.001–0.05 ng mL^?1, respectively. The intra-day and inter-day relative standard deviations (RSDs) at 0.5 ng mL^?1 concentration level (n?=?5) using a single-fiber were from 5.4 to 8.3 and 7.5 to 10.3%, respectively. The fiber-to-fiber RSDs % (n?=?3) was between 8.4 and 12.5%. Finally, the development method was applied to the analysis of various real samples.     

Determination of fluoride in toothpaste using headspace solid-phase microextraction and gas chromatography-flame ionization detection

A new method for determination of fluoride in toothpaste employing the headspace solid-phase microextraction (HS-SPME) followed by gas chromatography/flame ionization detection (GC/FID) has been proposed. It is a development of the method for determination of fluoride using trimethylchlorosilane (TMCS) as the derivatization reagent to form trimethylfluorosilane (TMFS), with the liquid/liquid extraction (LLE) step replaced by HS-SPME. To introduce the latter, it was necessary to determine the conditions of the reaction and to optimize the two stages of the SPME procedure: extraction and desorption. The parameters of the SPME analysis using carboxen/polydimethylsiloxane (CAR/PDMS) fiber were defined and compared with the corresponding ones for the LLE method, used as a reference. Also, these two methods were compared with respect to their linearity, precision, and accuracy. Results from toothpaste analyses using these two methods were highly correlated, indicating the potential to use the SPME extraction as an inexpensive and solventfree alternative to the LLE method.     

Field analysis of benzene, toluene, ethylbenzene and xylene in water by portable gas chromatography-microflame ionization detector combined with headspace solid-phase microextraction

In this work, portable gas chromatography-microflame ionization detection (portable GC-μFID) coupled to headspace solid-phase microextraction (HS-SPME) was developed for the field analysis of benzene, toluene, ethylbenzene and xylene (BTEX) in water samples. The HS-SPME parameters such as fiber coating, extraction times, stirring rate, the ratio of headspace volume to sample volume, and sodium chloride concentration were studied. A 65 μm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 900 rpm, 3.0 ml of headspace (1.0 ml water sample in 4.0 ml vial), and 35% sodium chloride concentration (w/v) were respectively chosen for the best extraction response. An extraction time of 1.0 min was enough to extract BTEX in water samples. The relative standard deviation (R.S.D.) for the procedure varied from 5.4% to 8.3%. The method detection limits (MDLs) found were lower than 1.5 μg/l, which was enough sensitive to detect the BTEX in water samples. The optimized method was applied to the field analysis of BTEX in wastewater samples. These experiment results show that portable GC-μFID combined with HS-SPME is a rapid, simple and effective tool for field analysis of BTEX in water samples.     

Quantitative analysis of benzene, toluene, and xylenes in urine by means of headspace solid-phase microextraction

A simple method for benzene, toluene, and xylenes (BTX) quantitative analyses in human urine was developed, using headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to mass spectrometry detection in the single ion monitoring mode. The developed method is solventless, non-invasive, requires small volume of sample (1 ml), shows high selectivity, sensitivity, repeatability, and linearity (correlation coefficients >0.998), providing a useful alternative to assess human exposure to BTX compounds due to occupational reasons or eventual exposure to organic solvents. Detection limit varies from 0.28 to 0.5 ppb (v/v).     

Analytical characteristics of the determination of benzene,toluene, ethylbenzene and xylenes in water by headspace solvent microextraction

Headspace solvent microextraction (HSM) is a novel method of sample preparation for chromatographic analysis. It involves exposing a microdrop of high-boiling point organic solvent extruded from the needle tip of a gas chromatographic syringe to the headspace above a sample. Volatile organic compounds are extracted and concentrated in the microdrop. Next, the microdrop is retracted into the microsyringe and injected directly into the chromatograph. HSM has a number of advantages, including renewable drop (no sample carryover), low cost, simplicity and ease of use, short time of analysis, high sensitivity and low detection limits, good precision, minimal solvent use, and no need for instrument modification. This paper presents analytical characteristics of HSM as applied to the determination of benzene, toluene, ethylbenzene and xylenes in water.     

Capillary extractors for "negligible depletion" sampling of benzene,toluene, ethylbenzene and xylenes by in-tube solid-phase microextraction

The suitability of "capillary extractors" is demonstrated for the "negligible depletion" extraction of benzene, toluene, ethylbenzene and xylenes in a clean-water matrix. Extraction set-up and major extractor parameters (length, internal diameter, and film thickness) are chosen to allow rugged analysis by GC with flame ionization detection. With the selected negligible extraction conditions, the efficiency for every consecutive extraction is about 2-3% of the dissolved amount.     

A novel reusable ionic liquid chemically bonded fused-silica fiber for headspace solid-phase microextraction/gas chromatography-flame ionization detection of methyl tert-butyl ether in a gasoline sample

A novel ionic liquid (IL) bonded fused-sil-ica fiber for headspace solid-phase microextraction (HS-SPME)/gas chromatography-flame ionization detection (GC-FID) of methyl tert-butyl ether (MTBE) in a gasoline sample was prepared and used. The new proposed chemically bonded fiber has better thermal stability and durability than its corresponding physically coated fiber. Another advantage is that no spacer was used for the purpose of bonding the IL to the surface of the fused-silica. The latter advantage makes the preparation of these fibers easier with lower cost than those prepared using sol–gel method. The ionic liquid 1-methyl-3-(3-trimethoxysilyl propyl) imidazolium bis(trifluoromethylsulfonyl) imide was synthesized and cross linked to the surface of the fused-silica fiber. Then, the chemically IL-modified fibers were applied to the headspace extraction of MTBE. The chemically IL-modified fibers showed improved thermal stability at temperatures up to 220 °C relative to the physically IL-modified fibers (180 °C). The chemically bonded IL film on the surface of the fused-silica fiber was durable over 16 headspace extractions without any significant loss of the IL film. The calibration graph was linear in a concentration range of 2–240 μg L⁻¹ (R² = 0.996) with the detection limit of 0.1 μg L⁻¹ level. The reproducibility (RSD %, n = 6) of the new IL bonded fused-silica fiber (8.9%) was better than the physically coated fiber (12%) suggesting that the proposed chemically IL-modified fiber is more robust than the physically IL-modified fiber. The optimum extraction conditions were the followings: 40 °C extraction temperature, 12 min extraction time, 30 s desorption time and sample agitation at 200 rpm.     

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 benzene, toluene, ethylbenzene and xylenes by headspace spectrophotometry with an atomic absorption apparatus.

In this study an atomic absorption spectrophotometer equipped with a selenium hollow-cathode lamp was used for analysis of BTEX (benzene, toluene, ethylbenzene and xylenes) in headspace of aqueous solutions. Initially effective factors on headspace such as volume of solution, stirring time, stirring speed, velocity of carrier gas, temperature, number of strippings, addition of salts and salt concentration were investigated and optimum conditions were selected. By addition of salt in different concentrations, different absorbances were obtained for headspace, therefore, binary mixtures of BTEX were analyzed with simultaneous equations. Obtained results agreed with actual amounts and repeatability was very good (RSD% < 3). Correlation coefficients (r) for calibration curves were about 0.999. This proposed method is comparable with absorbance determination of solution with respect to correlation coefficient, linear dynamic range, limit of detection (LOD) and relative standard deviation (RSD), but this method is less susceptible to interferences and more selective.     

Separation and determination of benzene, toluene, ethylbenzene and o-xylene compounds in water using directly suspended droplet microextraction coupled with gas chromatography-flame ionization detector

The directly suspended droplet microextraction (DSDME) technique coupled with the capillary gas chromatography-flame ionization detector (GC-FID) was used to determine BTEX compounds in aqueous samples. The effective parameters such as organic solvent, extraction time, microdroplet volume, salt effect and stirring speed were optimized. The performance of the proposed technique was evaluated for the determination of BTEX compounds in natural water samples. Under the optimal conditions the enrichment factors ranged from 142.68 to 312.13, linear range; 0.01-20 μg mL⁻¹, limits of detection; 0.8-7 ng mL⁻¹ for most analytes. Relative standard deviations for 0.2 μg mL⁻¹ of BTEX in water were in the range 1.81-2.47% (n = 5). The relative recoveries of BTEX from surface water at spiking level of 0.2 μg mL⁻¹ were in the range of 89.87-98.62%.     

Determination of benzene,toluene, ethylbenzene,and xylenes in urine by purge and trap gas chromatography

A method for determination of benzene, toluene, ethylbenzene, and xylenes (BTEX) in urine is described. Determination is performed by dynamic headspace (purge and trap) gas chromatography with photoionization detection. The features of the described method, i.e. detection limits of 15–35 ng L^–1, relative standard deviations of 0.2–10%, accuracy of 80–100%, removal of interference of many compounds present in urine, sharp chromatographic peaks because of cryogenic refocusing, no sample preparation, make it convenient for biological monitoring of exposure to low levels of BTEX. However, the method is time‐consuming and sophisticated.     

Modified dispersive liquid-liquid microextraction for pre-concentration of benzene, toluene, ethylbenzene and xylenes prior to their determination by GC

We have developed a modified method for the extraction and preconcentration of benzene, toluene, ethylbenzene and xylenes (BTEX) in aqueous samples. It based on dispersive liquid-liquid microextraction along with solidification of floating organic microdrops. The dispersion of microvolumes of an extracting solvent into the aqueous occurs without dispersive solvent. Various parameters have been optimized. BTEX were quantified via GC with FID detection. Under optimized conditions, the preconcentration factors range from 301 to 514, extraction efficiencies from 60 to 103 %, repeatabilities from 2.2 to 4.1 %, and intermediate precisions from 3.5 to 7.0 %. The relative recovery for each analyte in water samples at three spiking levels is >85.6 %, with a relative standard deviation of <7.4 %.

分散液液微萃取-气相色谱法测定水中苯、甲苯和二甲苯

以CHCl3为萃取剂,丙酮为分散剂,建立了基于分散液液微萃取(DLLME)结合气相色谱测定水样中苯、甲苯和二甲苯含量的新方法。实验对影响萃取效率的因素进行优化,萃取条件为:在1.0mL含有50g/LNaCl的样品溶液中加入40.0μLCHCl3和0.16mL丙酮,振荡分散均匀后,以400r/min离心5min,取萃取溶剂1.00μL直接进样分析。本方法线性范围为0.8～200μg/mL,相关系数r0.9980,检出限为0.1μg/mL,回收率分别在93.5%～102.1%之间。将该方法与液液萃取法、单滴微萃取相比较,具有操作简单、富集效率高和灵敏度高等特点。     

Combination of solid-phase extraction-hollow fiber for ultra-preconcentration of some triazole pesticides followed by gas chromatography-flame ionization detection

In this study, an extraction and preconcentration technique using solid-phase extraction (SPE) along with hollow fiber (HF) has been developed as an ultra-preconcentration technique for some triazole pesticides in aqueous samples. Triazole pesticides were employed as model compounds to assess the method and were monitored by gas chromatography-flame ionization detection (GC-FID). Initially, an aqueous solution of target analytes was passed through an RP-8 SPE cartridge and then the adsorbed analytes were eluted with μL amounts of toluene. The collected elute was slowly introduced into an HF that had one end blocked. This allowed precipitation inside the lumen and pores of the HF. Finally, the obtained HF was mounted on a home-made solid-phase microextraction syringe and entered into the GC injection port for thermal desorption-GC analysis. The effect of various experimental parameters including injection port temperature, desorption time, state of HF, washing solvent, elution solvent and its volume, sample volume, etc. were investigated for finding the optimum conditions. The calibration graphs were linear in the ranges of 2-1000 ng/mL (penconazole and hexaconazole), 5-1000 ng/mL (tebuconazole), 15-1000 ng/mL (triticonazole) and the detection limits (LODs) ranged from 0.6 to 4.5 ng/mL. The enhancement factors were in the range of 870-950. The relative standard deviations (RSD%) for five repeated experiments (C=250 ng/mL of each pesticide) varied from 4.5 to 8.7%. The relative recoveries obtained for analytes in grape juice samples, spiked with different levels of each pesticide, were in the range of 87-119%.     

Evaluation of the solid-phase microextraction fiber coated with single walled carbon nanotubes for the determination of benzene,toluene, ethylbenzene,xylenes in aqueous samples

A solid-phase microextraction (SPME) fiber coated with single walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition and treated at 500 °C in H₂ stream. In order to evaluate the characteristics of the obtained fiber, it was applied in the headspace solid-phase microextraction (HS-SPME) of benzene, toluene, ethylbenzene and xylenes (BTEX) from water sample and quantification by gas chromatography with flame ionization detection (GC-FID). The results indicated that the thermal treatment with H₂ enhanced the extraction of the SWCNTs fiber for BTEX significantly. Thermal stability and durability of the fiber were also investigated, showing excellent stability up to 350 °C and life time over 120 times. In the comparison with the commercial CAR–PDMS fiber, the SWCNTs fiber showed similar and higher extraction efficiencies for BTEX. Under the optimized conditions, the linearity, LODs (S/N = 3) and LOQs (S/N = 10) of the method based on the SWCNTs fiber were 0.5–50.0, 0.005–0.026 and 0.017–0.088 μg/L, respectively. Repeatability for one fiber (n = 3) was in the range of 1.5–5.6% and fiber-to-fiber reproducibility (n = 3) was in the range of 4.2–8.3%. The proposed method was successfully applied in the analysis of BTEX compounds in seawater, tap water and wastewater from a paint plant.     

Optimization of headspace solid-phase microextraction by means of an experimental design for the determination of methyl tert.-butyl ether in water by gas chromatography-flame ionization detection

A procedure for determination of methyl tert.-butyl ether (MTBE) in water by headspace solid-phase microextraction (HS-SPME) has been developed. The analysis was carried out by gas chromatography with flame ionization detection. The extraction procedure, using a 65-microm poly(dimethylsiloxane)-divinylbenzene SPME fiber, was optimized following experimental design. A fractional factorial design for screening and a central composite design for optimizing the significant variables were applied. Extraction temperature and sodium chloride concentration were significant variables, and 20 degrees C and 300 g/l were, respectively chosen for the best extraction response. With these conditions, an extraction time of 5 min was sufficient to extract MTBE. The calibration linear range for MTBE was 5-500 microg/l and the detection limit 0.45 microg/l. The relative standard deviation, for seven replicates of 250 microg/l MTBE in water, was 6.3%.     

Diffusion-based calibration for solid-phase microextraction of benzene, toluene, ethylbenzene, p-xylene and chlorobenzenes from aqueous samples

Short-term solid-phase microextraction (SPME) was performed to test a recently proposed semi-empirical model for the prediction of concentrations of analyte in water samples from the fibre-extracted mass without further calibration. The mass uptake rates obtained for benzene, toluene, ethylbenzene and p-xylene (BTEX) differ considerably from the before published, showing that interfibre comparability is a serious issue. The relative prediction errors are between -55% for benzene and +82% for p-dichlorobenzene under optimal conditions, i.e. they are by an order of magnitude higher than originally published. A sensitivity analysis shows the dominant influence of the estimated thickness of the diffusional boundary layer around the fibre on the concentration predicted. Empirical modification of the model equation for this parameter yields satisfactory results under the conditions tested for both BTEX and the selected chlorobenzenes.