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。     

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.     

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.     

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.     

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.     

Use of in-tube sorptive extraction techniques for determination of benzene, toluene, ethylbenzene and xylenes in soft drinks

A comparison is made between static headspace analysis and headspace solid-phase dynamic extraction (HS-SPDE) for the quantitative determination of trace level BTEX solvents (benzene, toluene, ethylbenzene and o-, m-, and p-xylene) in soft drinks. Two non-polar extraction phases were investigated for SPDE using an automated sampler with a gas-tight syringe equipped with a special needle coated on the inside with the extraction phase. Following adsorption onto the phase, the analytes were thermally desorbed directly into a GC-MS. The techniques were optimised and evaluated by analysis of spiked soft drink samples. The use of the SPDE device gave comparable results to the static headspace method, with lower detection limits for some compounds, and also offers advantages for applications where lower temperatures are preferred.     

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.     

Multivariate optimization of headspace‐GC for the determination of monoaromatic compounds (benzene,toluene, ethylbenzene,and xylenes) in waters and wastewaters

The objective of this study was to optimize, by employing a central composite rotatable design, and validate an analytical method to detect and quantify monoaromatic compounds (benzene, toluene, ethylbenzene, and xylenes) in waters and wastewaters by using headspace extraction followed by GC coupled with photoionization detection. The extraction parameters optimized were: salinity, sample volume, incubation time, and extraction temperature. The results revealed that the sample volume was the most significant parameter in the extraction process, whereas the salinity effect was negligible, which extends the applicability of the analytical method to waters with different salinities. Finally, the studied method was very selective and, at the optimal extraction conditions (15 mL sample volume, 15 min incubation time, and temperature of 70°C), presented excellent repeatability (<4%), linearity (R > 0.999 for each compound), and sensitivity, since very low LODs (0.13–0.48 μg/L) and LOQs (0.43–1.61 μg/L) were achieved.     

Disposable ionic liquid coating for headspace solid-phase microextraction of benzene, toluene, ethylbenzene, and xylenes in paints followed by gas chromatography-flame ionization detection

Solid-phase microextraction (SPME) with a disposable ionic liquid (IL) coating was developed for headspace extraction of benzene, toluene, ethylbenzene, and xylenes (BTEX) in paints. The SPME fiber was coated with IL prior to every extraction, then the analytes were extracted and desorbed on the injection port of gas chromatography, and finally the IL coating on the fiber was washed out with solvents. The coating and washing out of IL from the fiber can be finished in a few minutes. This disposable IL-coated fiber was applied to determine BTEX in water-soluble paints with results in good agreement with that obtained by using commercially available SPME fibers. For all the four studied paints samples, the benzene contents were under the detection limits, but relatively high contents of toluene, ethylbenzene and xylenes (56-271 microg g(-1)) were detected with spiked recoveries in the range of 70-114%. Compared to the widely used commercially available SPME fibers, this proposed disposable IL-coated fiber has much lower cost per determination, comparable reproducibility (RSD < 11%), and no carryover between each determination. Considering that IL possess good extractability for various organic compounds and metals ions, and that task-specific IL can be designed and synthesized for selective extraction of target analytes, this disposable IL coating SPME might has great potential in sample preparation.     

Development of a versatile,easy and rapid atmospheric monitor for benzene,toluene, ethylbenzene and xylenes determination in air

A new procedure for the passive sampling in air of benzene, toluene, ethylbenzene and xylene isomers (BTEX) is proposed. A low-density polyethylene layflat tube filled with a mixture of solid phases provided a high versatility tool for the sampling of volatile compounds from air. Several solid phases were assayed in order to increase the BTEX absorption in the sampler and a mixture of florisil and activated carbon provided the best results. Direct head-space-gas chromatography–mass spectrometry (HS-GC–MS) measurement of the whole deployed sampler was employed for a fast determination of BTEX. Absorption isotherms were used to develop simple mathematical models for the estimation of BTEX time-weighted average concentrations in air. The proposed samplers were used to determine BTEX in indoor air environments and results were compared with those found using two reference methodologies: triolein-containing semipermeable membrane devices (SPMDs) and diffusive Radiello samplers. In short, the developed sampling system and analytical strategy provides a versatile, easy and rapid atmospheric monitor (VERAM).     

Programmed temperature vaporizer based method for the sensitive determination of trihalomethanes and benzene,toluene, ethylbenzene and xylenes in soils

A methodology based on the coupling of a headspace autosampler with a GC and a MS detector operating in SIM mode has been developed for the determination of volatile organic compounds (THMs and BTEX) in soils. The GC device used is equipped with a programmable temperature vaporizer (PTV) packed with Tenax-TA^® to introduce the samples (the injection mode used was solvent vent), and a modular accelerated column heater (MACH™) to control column temperature. The proposed measurement procedure reduces the sample pretreatment step to a minimum. Combined use of solvent vent injection mode and mass spectrometry detection allows a highly sensitive method to be proposed, with limits of detection of the order of ng/kg for all the target compounds. Furthermore, the capillary column used allows rapid separations of compounds in less than 4.60 min, affording a very short total analysis cycle time of 9 min.     

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.     

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.     

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).     

Ultrafast gas chromatography method with direct injection for the quantitative determination of benzene,toluene, ethylbenzene,and xylenes in commercial gasoline

Benzene, toluene, ethylbenzene, and xylenes are some of the most hazardous constituents found in commercial gasoline samples; therefore, these components must be monitored to avoid toxicological problems. We propose a new routine method of ultrafast gas chromatography coupled to flame ionization detection for the direct determination of benzene, toluene, ethylbenzene, and xylenes in commercial gasoline. This method is based on external standard calibration to quantify each compound, including the validation step of the study of linearity, detection and quantification limits, precision, and accuracy. The time of analysis was less than 3.2 min, with quantitative statements regarding the separation and quantification of all compounds in commercial gasoline samples. Ultrafast gas chromatography is a promising alternative method to official analytical techniques. Government laboratories could consider using this method for quality control.     

Extraction optimization of polycyclic aromatic hydrocarbons by alcoholic-assisted dispersive liquid-liquid microextraction and their determination by HPLC

A sensitive method for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) using alcoholic-assisted dispersive liquid-liquid microextraction (AA-DLLME) and HPLC was developed. The extraction procedure was based on alcoholic solvents for both extraction and dispersive solvents. The effective parameters (type and volume of extraction and dispersive solvents, amount of salt and stirring time) on the extraction recovery were studied and optimized utilizing factorial design (FD) and central composite design (CCD). The best recovery was achieved by FD using 2-ethyl-1-hexanol as the extraction solvent and methanol as the dispersive solvent. The results showed that volume of dispersive solvent and stirring time had no effect on the recovery of PAHs. The optimized conditions were 145 μL of 2-ethyl-1-hexanol as the extraction solvent and 4.2% w/v of salt (NaCl) in sample solution. The enrichment factors of PAHs were in the range of 310-325 with limits of detection of 0.002-0.8 ng/mL. The linearity was 0.01-800 ng/mL for different PAHs. The relative standard deviation (RSD) for intra- and inter-day of extraction of PAHs were in the range of 1.7-7.0 and 5.6-7.3, respectively, for five measurements. The method was also successfully applied for the determination of PAHs in environmental water samples.     

Sensitive determination of carbamates in fruit and vegetables by a combination of solid-phase extraction and dispersive liquid-liquid microextraction prior to HPLC

We report on a new method for sample pretreatment. It is based on solid-phase extraction combined with dispersive liquid-liquid microextraction (SPE-DLLME) and was applied to the determination of carbamates in apple and cucumber. The carbamates carbofuran, carbaryl, and pirimicarb were first extracted from samples by SPE. The analytes were then eluted from the sorbent with acetonitrile, and the DLLME technique was then applied to the resulting eluate. Finally, the analytes in the extraction solvent were determined by HPLC. Several parameters affecting the SPE-DLLME process were optimized. The new method provides enrichment factors that range from 5,400 to 7,650. Calibration plots are linear in the range from 0.25 to 100?μg?kg^?1 for carbofuran and carbaryl, and from 0.10 to 100?μg?kg^?1 for pirimicarb, with correlation coefficient (r²) ranging from 0.9980 to 0.9997. The limits of detection range from 5 to 60?pg?kg^?1 (at S/N?=?3). The method was successfully applied to the extraction and sensitive determination of carbamates in apple and cucumber samples.

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.     

Separation of BTEX compounds (benzene,toluene, ethylbenzene and xylenes) from aqueous solutions using adsorption process

A commercial synthetic zeolite (Na-ZSM-5) was modified with an organic surfactant, HDTMA-Br. Then both unmodified and modified zeolite (SMZ-100) were tested to adsorb Benzene, Toluene, Ethylbenzene and Xylene (BTEX) compounds from water solution. Adsorption tests were done in batch conditions at the ambient temperature (20?°C) and pressure. Adsorbents were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption-desorption isotherms and field emission scanning electron microscopy (FE-SEM) and characterization results proved the existence of surfactant on the surface of the adsorbent. In all cases, the modified zeolite sample, because of increasing the hydrophobicity of its surface, exhibited higher adsorption capacity in comparison with unmodified zeolite. Also, for each adsorbent, the adsorption capacity follows the order: E?>?X?>?T?>?B. In equilibrium experiments, Langmuir isotherm model fitted the equilibrium data better than the Freundlich model. In kinetic experiments, the pseudo-second order model described the kinetic data better than the other models.     

Headspace microdrop analysis--an alternative test method for gasoline diluent and benzene,toluene, ethylbenzene and xylenes in used engine oils

The primary standard test method used for the determination of gasoline diluent in used engine oils is method D 3525-93 of the American Society for Testing and Materials (ASTM), which involves direct injection of used oil onto a packed GC column and flame ionization detection. Recently, we have utilized a new headspace sampling method: headspace solvent microextraction (HSM), for GC and GC-MS analysis of gasoline diluent in used engine oils. High resolution capillary columns can be used without the necessity for the use of inlet cryogenic cooling or expensive sampling interfaces. This analytical method, which we generically refer to as headspace microdrop analysis yields results comparable to those obtained using the ASTM method, with the added benefit that it allows the quantification of individual volatile diluent components, including benzene, toluene, ethylbenzene and the xylenes.