Quantification of volatile sulfur compounds in complex gaseous matrices by solid-phase microextraction

Procedures were assessed for quantifying nine volatile sulfur compounds found in complex gaseous samples collected at a biogas-production plant and a sewage treatment plant. The target compounds were extracted by solid-phase microextraction (using the 75-microm Carboxen-polydimethylsiloxane fiber coating) at 22 degrees C for 20 min, and analyzed by GC-MS. Detection limits ranged between 1 pptv (v/v) for carbon disulfide and 470 pptv (v/v) for hydrogen sulfide. High amounts of organic compounds were found during full-scan analysis of the samples and standard additions to individual sub-samples revealed that the analysis was subject to matrix effects. However, the functions obtained by standard additions were still linear and quantification was possible for all the compounds tested except hydrogen sulfide. No detectable losses were observed during storage in the sampling containers, made of Tedlar film, over a storage period of 20 h. However, water permeated through the walls and the relative humidity in the bag increased during storage until it reached the ambient level. Finally, it was shown that the drying agent, CaCl2, caused no detectable losses of any of the compounds.     

Flow-assisted automated solid-phase microextraction for the determination of chloroethers in aqueous matrices

In this study a method of flow-assisted automated solid-phase microextraction (FA-SPME) was developed for the determination of organic pollutants in aqueous samples. A CTC Combi-PAL autosampler coupled with gas chromatography–mass spectrometry (GC–MS) was used to automate the entire extraction process. In this method, the SPME fibre was exposed to 100 mL of sample in a direct immersion mode for 10 min. After exposure, the fibre was desorbed at the injection port of GC–MS. To demonstrate the applicability of FA-SPME, chloroethers were selected as model compounds. Good linear correlation was found over a concentration range of 0.5–100 µg/L. The detection limits of the method were determined between 0.02 and 0.05 µg/L with the coefficients of determination (R²) from 0.9980 to 0.9996. The relative standard deviations (RSDs) of the FA-SPME for three sequential FA-SPME analyses were determined to be in the range between 1.2% and 6.2% (n = 3). The applicability of the method was assessed by means of recovery studies and satisfactory values for all compounds were obtained. This optimised method was used in the analysis of water and human urine samples to show the matrix effect on FA-SPME. This FA-SPME/GC–MS is substantially faster and suitable for the routine continuous flow-mode environmental monitoring applications.     

Multiple headspace solid-phase microextraction for the quantitative determination of volatile organic compounds in multilayer packagings

The theory of multiple headspace solid-phase microextraction (HS-SPME) and a method based on multiple HS-SPME for the quantitative determination of volatile organic compounds (VOCs) in packaging materials is presented. The method allows the direct analysis of solid samples without using organic solvents to extract analytes. Multiple headspace solid-phase microextraction is a stepwise method proposed to eliminate the influence of the sample matrix on the quantitative analysis of solid samples by HS-SPME. Different amounts of packaging and different volumes of standard solution were studied in order to remove a substantial quantity of analytes from the headspace at each extraction and obtain the theoretical exponential decay of the peak area of the four successive extractions and, thus, the total area was calculated from these four extractions. In addition, two fibres were compared: carboxen-polydimethylsiloxane (CAR-PDMS) and divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS), as they showed differences in the linearity of the exponential decay with the number of extractions depending on the compound. The CAR-PDMS fibre was better for the VOCs with a low molecular mass, whereas the DVB-CAR-PDMS fibre was better for the VOCs with a high molecular mass. Finally, the method was characterised in terms of linearity, detection limit and reproducibility and applied to analyse four multilayer packaging samples with different VOCs contents.     

Active single-drop microextraction for the determination of gaseous diisocyanates

Heterocyclic amines (HAs) were analysed in meat extract samples using a new method based on pressurised liquid extraction (PLE) and liquid chromatography-tandem mass spectrometry. This method combines the use of a pressurised fluid with a triple quadrupole MS/MS system, resulting in benefits from both systems: high extraction efficiency and sensitivity. The effects of solvent type and PLE operational parameters, such as temperature and extraction time, were studied to obtain maximum recovery of the analytes with minimum contamination. HA extraction was best achieved using dichloromethane/acetone (50/50, v/v) at 80 degrees C for 10 min. Recoveries ranged from 45% to 79% with good quality parameters: limit of detection values between 0.02 and 1 ng g(-1), linearity (r(2)>0.997), and run-to-run and day-to-day precisions with relative standard deviations lower than 13% achieved at both low (0.20 microg g(-1)) and medium (1.0 microg g(-1)) concentrations. This method reduces sample manipulation and total extraction time by nearly four-fold compared to conventional solid phase extraction. The optimised method was validated using laboratory reference material based on a meat extract, and was successfully applied to HA analysis in several cooked beef samples.     

固相微萃取涂层的制备及其在水体和气态基质中的应用

采用物理涂渍的方法制备了γ-Al2O3固相微萃取涂层。通过γ-Al2O3固相微萃取（SPME）-气相色谱（GC）联用技术,对水中痕量苯系物苯、甲苯、乙苯、二甲苯异构体(BTEXs)进行萃取分析,结果表明该涂层具有热稳定性强(最高使用温度可达350 ℃)、灵敏度高(检测限为1~10 μg/L)以及制备重复性好（相对标准偏差为8.3%）的特点;同时该涂层对气态基质中的污染物亦可进行萃取分析。     

Application of solid-phase microextraction and gas chromatography-mass spectrometry to the determination of volatile organic compounds in end-exhaled breath samples

Analysis of exhaled air is of particular interest as an indicator of health as well as a tool for the diagnosis of diseases. It is also a very attractive procedure for the biological control of the exposition to hazardous solvents. This kind of analysis presents numerous advantages over other methods, the most important being that it is not an invasive procedure and, therefore, it is well accepted and can be applied to a wide range of compounds. Furthermore, the analysis is simplified since the matrix is less complex that in the case of blood or urine. In spite of these obvious advantages and the good results obtained, analysis of exhaled air is not in daily use, probably due to the fact that there are no normalized systems of sampling, thus making the interpretation of the results difficult. In this paper, a method for the determination of tetrachloroethylene in exhaled air using solid-phase microextraction is presented. This method, which can be applied to other volatile organic compounds, was developed with special emphasis of end-exhaled breath sampling. The sample is collected in a glass tube whose ends are closed once the exhalation is finished. The tube has an orifice sealed with a septum through which the fiber is inserted. Then, the fiber is desorbed in the injector of a gas chromatograph and the analysis is accomplished using mass spectrometry for the identification and quantification of the components. The proposed system avoids the need of complex sampling equipment and allows analysis of the alveolar fraction. Additionally, the system is economical and easy to handle, thus facilitating the development of normalized methods and its routine use in field studies.     

Application of the polysilicone fullerene coating for solid-phase microextraction in the determination of semi-volatile compounds

Solid-phase microextraction using polysilicone fullerene (PF) coating has been applied for the determination of semi-volatile compounds. Detection limits at the 10 ng l(-1) to approximately microg l(-1) level were achieved using flame ionization detection. A wide linear range was obtained with precision below 7% relative standard deviation. Parameters that affect the extraction process were investigated, which included sampling time, desorption time, sampling temperature, and salting out effect. Compared to the non-polar commercial polydimethylsiloxane (PDMS) coating, the PF coating has higher extraction efficiency, better selectivity and greater sensitivity for aromatic compounds. The experimental results revealed the thermal stability and life span are superior to commercially available PDMS. The PF coating has been demonstrated to possess planarity molecular recognition. The theoretical study confirmed that quantification is feasible under non-equilibrium conditions by use of the PF coating.     

Application of solid-phase microextraction for the determination of pyrethroid residues in vegetable samples by GC-MS

A solid-phase microextraction (SPME) method has been developed for the determination of 7 pyrethroid insecticides (bifenthrin, lambda-cyhalothrin, permethrin, cyfluthrin, cypermethrin, fenvalerate, and tau-fluvalinate) in water, vegetable (tomato), and fruit (strawberry) samples, based on direct immersion mode and subsequent desorption into the injection port of a GC/MS. The SPME procedure showed linear behavior in the range tested (0.5-50 microg L(-1) in water and 0.01-0.1 mg kg(-1) in tomato) with r(2) values ranging between 0.97 and 0.99. For water samples limits of detection ranged between 0.1 and 2 microg L(-1 )with relative standard deviations lower than 20%. Detection limits for tomato samples were between 0.003 and 0.025 mg kg(-1) with relative standard deviations around 25%. Finally, the SPME procedure has been applied to vegetable (tomato) and fruit (strawberry) samples obtained from an experimental plot treated with lambda-cyhalothrin, and in both cases the analyte was detected and quantified using a calibration curve prepared using blank matrix. SPME has been shown to be a simple extraction technique which has a number of advantages such as solvent-free extraction, simplicity, and compatibility with chromatographic analytical systems. Difficulties with the correct quantification in a complex matrix are also discussed.     

Application of solid-phase microextraction and gas chromatography-mass spectrometry for the determination of chlorophenols in leather

This paper proposes a new analytical procedure based on the headspace solid‐phase microextraction (HS‐SPME) technique and gas chromatography‐selected ion monitoring‐mass spectrometry (GC‐SIM‐MS) for the determination of 16 phenols extracted from leather samples. The optimized conditions for the HS‐SPME were obtained through two experimental designs – a two‐level fractional factorial design followed by a central composite design – using the commercial SPME fiber polyacrylate 85 μm (PA). The best extraction conditions were as follows: 200 μL of derivatizing agent (acetic anhydride), 20 mL of saturated aqueous NaCl solution and extraction time and temperature of 50 min and 75°C, respectively. All optimized conditions were obtained with fixed leather sample mass (250 mg), vial volume (40 mL) and phosphate buffer pH (12) and concentration (50 mmol/L). Detection limits ranging from 0.03 to 0.20 ng/g, and relative standard deviation (RSD) lower than 10.23% (n=6) for a concentration of 800 ng/g (chlorophenols) and 1325 ng/g (2‐phenylphenol) in the splitless mode were obtained. The recovery was studied at three concentration levels by adding different amounts of phenols to the leather sample and excellent recoveries ranging from 90.0 to 107.2% were obtained. The validated method was shown to be suitable for the quantification of phenols in leather samples, as it is simple, relatively fast and sensitive.     

Application of solid-phase microextraction in analytical toxicology

Solid-phase microextraction (SPME) is a miniaturized and solvent-free sample preparation technique for chromatographic–spectrometric analysis by which the analytes are extracted from a gaseous or liquid sample by absorption in, or adsorption on, a thin polymer coating fixed to the solid surface of a fiber, inside an injection needle or inside a capillary. In this paper, the present state of practical performance and of applications of SPME to the analysis of blood, urine, oral fluid and hair in clinical and forensic toxicology is reviewed. The commercial coatings for fibers or needles have not essentially changed for many years, but there are interesting laboratory developments, such as conductive polypyrrole coatings for electrochemically controlled SPME of anions or cations and coatings with restricted-access properties for direct extraction from whole blood or immunoaffinity SPME. In-tube SPME uses segments of commercial gas chromatography (GC) capillaries for highly efficient extraction by repeated aspiration–ejection cycles of the liquid sample. It can be easily automated in combination with liquid chromatography but, as it is very sensitive to capillary plugging, it requires completely homogeneous liquid samples. In contrast, fiber-based SPME has not yet been performed automatically in combination with high-performance liquid chromatography. The headspace extractions on fibers or needles (solid-phase dynamic extraction) combined with GC methods are the most advantageous versions of SPME because of very pure extracts and the availability of automatic samplers. Surprisingly, substances with quite high boiling points, such as tricyclic antidepressants or phenothiazines, can be measured by headspace SPME from aqueous samples. The applicability and sensitivity of SPME was essentially extended by in-sample or on-fiber derivatization. The different modes of SPME were applied to analysis of solvents and inhalation narcotics, amphetamines, cocaine and metabolites, cannabinoids, methadone and other opioids, fatty acid ethyl esters as alcohol markers, γ-hydroxybutyric acid, benzodiazepines, various other therapeutic drugs, pesticides, chemical warfare agents, cyanide, sulfide and metal ions. In general, SPME is routinely used in optimized methods for specific analytes. However, it was shown that it also has some capacity for a general screening by direct immersion into urine samples and for pesticides and other semivolatile substance in the headspace mode.     

Application of single-drop microextraction and comparison with solid-phase microextraction and solid-phase extraction for the determination of alpha- and beta-endosulfan in water samples by gas chromatography-electron-capture detection

Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. The 98/83 European Directive requires the measurement of pesticides residues at a target concentration of 1.0 microg/l in surface water and 0.1 microg/l in drinking water. In order to reach the level of detection required, efficient extraction techniques are necessary. The application of a new extraction technique: single-drop microextraction (SDME), followed by gas chromatography with electron-capture detection, was assessed for determining alpha-endosulfan and beta-endosulfan in water samples. Experimental parameters which control the performance of SDME, such as selection of microextraction solvent and internal standard, optimization of organic drop volume, effects of sample stirring, temperature and salt addition, and sorption time profiles were studied. Once SDME was optimized, analytical parameters such as linearity, precision, detection and quantitation limits, plus matrix effects were evaluated. The SDME method was compared with solid-phase microextraction and solid-phase extraction with the aim of selecting the most appropriate method for a certain application.     

Characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model

Water-to-polydimethylsiloxane (PDMS) and gas-to-PDMS sorption coefficients have been compiled for 170 gaseous and organic solutes. Both sets of sorption coefficients were analyzed using the Abraham solvation parameter model. Correlations were obtained for both "dry" headspace solid-phase microextraction and conventional "wet" PDMS coated surfaces. The derived equations correlated the experimental water-to-PDMS and gas-to-PDMS data to better than 0.17 and 0.18 log units, respectively. In the case of the gas-to-PDMS sorption coefficients, the experimental values spanned a range of approximately 11 log units.     

Application of bar adsorptive microextraction to determine trace organic micro-pollutants in environmental water matrices

The present work proposes the application of bar adsorptive micro-extraction (BAµE) coated with an N-vinylpyrrolidone polymer (NVP) combined with micro-liquid desorption (200 µL) followed by high-performance liquid chromatography with diode array detection (BAµE(NVP)-µLD/HPLC-DAD) for the determination of trace levels of emerging organic micro-pollutants in environmental water matrices. The model compounds selected include an antibacterial/antifungal agent (triclosan), two pharmaceuticals (carbamazepine and diclofenac) and two steroid hormones (17α-ethinylestradiol and 17β-estradiol), in which the latter three were recently included in the European Union watch list of substances to be monitored in the field of water policy. Assays performed on 25 mL of ultrapure water samples spiked at the 8.0 µg L^?1 level yielded average recoveries ranging from 81.9 to 102.4% for the compounds studied using optimised experimental conditions. The proposed analytical methodology demonstrated suitable detection limits (0.02–0.10 µg L^?1) and good linear dynamic ranges (0.1–20.0 µg L^?1) with determination coefficients higher than 0.9909. Using the standard addition method (SAM), the present analytical approach was applied on environmental water matrices, including surface, sea, river and groundwaters. The proposed method proved to be a suitable and alternative sorption-based static micro-extraction technique for monitoring trace levels of organic micro-pollutants in environmental water matrices.     

Evaluation of solid-phase microextraction with PDMS for air sampling of gaseous organophosphate flame-retardants and plasticizers

As an inexpensive, simple, and low-solvent consuming extraction technique, the suitability of solid-phase microextraction (SPME) with polydimethylsiloxane (PDMS) sorbent was investigated as a quantitative method for sampling gaseous organophosphate triesters in air. These compounds have become ubiquitous in indoor air, because of their widespread use as additive flame retardants/plasticizers in various indoor materials. Results obtained by sampling these compounds at controlled air concentrations using SPME and active sampling on glass fibre filters were compared to evaluate the method. A constant linear airflow of 10 cm s^–1 over the fibres was applied to increase the extraction rate. For extraction of triethyl phosphate with a 100-m PDMS fibre, equilibrium was achieved after 8 h. The limit of detection was determined to be less than 10 pg m^–3. The PDMS–air partition coefficients, K_fs, for the individual organophosphate triesters were determined to be in the range 5–60×10⁶ at room temperature (22–23°C). Air measurements were performed utilising the determined coefficients for quantification. In samples taken from a lecture room four different airborne organophosphate esters were identified, the most abundant of which was tris(chloropropyl) phosphate, at the comparatively high level of 1.1 g m^–3. The results from SPME and active sampling had comparable repeatability (RSD less than 17%), and the determined concentrations were also similar. The results suggest that the investigated compounds were almost entirely associated with the gaseous phase at the time and place sampled.     

Semiquantitative determination of off-notes in mint oils by solid-phase microextraction

Mint essential oils are produced by the steam distillation of dried or partially dried harvested plant material. In the United States, harvesting is done mechanically so that any weeds found in the field are concomitantly harvested. Steam distillation of contaminated plant material leads to off-notes in the oil, which are currently determined by a sensory panel. Furthermore, nonoptimized distillation conditions can lead to the thermal degradation of carbohydrates and proteins resulting also in the formation of very volatile off top-notes. As a result, the use of a nonequilibrated solid-phase microextraction (SPME) procedure to determine the off-notes is evaluated. The results of this evaluation include a combination of semiquantitative data, odor threshold data, and mathematical data manipulation to ascertain the capabilities of a SPME approach. The results are correlated with sensory panel data to yield a relatively rapid analytical methodology that can be used either in place of or in support of sensory analyses. The main advantage of the technique described is to provide some semiquantitative data in support of the odor-panel screening of mint oils for off-notes. Based on the data presented in this report, it is believed that this has been successfully demonstrated.     

Determination of gaseous toluene diisocyanate by use of solid-phase microextraction with on-fibre derivatisation

An SPME method was developed for sampling gaseous 2,4-toluene diisocyanate (2,4-TDI) involving derivatisation of the isocyanate by reacting with dibutylamine (DBA). The TDI-DBA derivative thus formed was determined by LC-MS-MS utilising atmospheric pressure chemical ionisation (APCI). As a first step, DBA was loaded onto a poly(dimethylsiloxane)/divinylbenzene (PDMS-DVB) fibre coating by direct vapour-phase extraction of a highly concentrated diethyl ether solution of DBA. The DBA-loaded fibre was then exposed to an artificially generated atmosphere of gaseous 2,4-TDI. The linearity of the method ranged from 52.8 to 3100 microg m(-3) (6.8 to 400 ppbv) with a sampling time of 60 min. The proposed method has been applied to 2,4-TDI determination in an artificially generated dynamic standard atmosphere, yielding an approximate method detection limit (MDL) of 2 microg m(-3) (0.25 ppbv). This concentration is one twentieth of the Occupational Safety and Health Administration (OSHA) 8-hour time-weighted average (TWA) exposure limit. The sampler with the PDMS-DVB-DBA coating was found to be stable and retains the required amount of DBA for at least 10 days, an important feature for sampling systems with potential in-situ applications.     

Rapid determination of organotin compounds by headspace solid-phase microextraction

Headspace solid-phase microextraction (SPME) followed by gas chromatography (GC) coupled to pulsed flame photometric detection have been investigated for the simultaneous speciation analysis of 14 organotin compounds, including methyl-, butyl-, phenyl-, and octyltins compounds. The analytical process (sorption on SPME fibre and thermal desorption in GC injection port) has been optimised using experimental designs. Six operating factors were considered in order to evaluate their influence on the performances of a SPME-based procedure. The evaluation of accuracy, precision and limits of detection (LODs) according to ISO standards and IUPAC recommendations has allowed the method to be validated. The LODs obtained for the 14 studied organotins compounds are widely sub-ng(Sn) l(-1). The precision evaluated using relative standard deviation ranges between 9 and 25% from five determinations of the analytes at 0.25-125 ng(Sn) l(-1) concentrations. The accuracy was studied throughout the analysis of spiked environmental samples. These first results show that headspace SPME appears really as attractive for organotins determination in the environment and the monitoring of their biogeochemical cycle.     

Determination of gaseous toluene diisocyanate by use of solid-phase microextraction with on-fibre derivatisation

An SPME method was developed for sampling gaseous 2,4-toluene diisocyanate (2,4-TDI) involving derivatisation of the isocyanate by reacting with dibutylamine (DBA). The TDI-DBA derivative thus formed was determined by LC–MS–MS utilising atmospheric pressure chemical ionisation (APCI). As a first step, DBA was loaded onto a poly(dimethylsiloxane)/divinylbenzene (PDMS–DVB) fibre coating by direct vapour-phase extraction of a highly concentrated diethyl ether solution of DBA. The DBA-loaded fibre was then exposed to an artificially generated atmosphere of gaseous 2,4-TDI. The linearity of the method ranged from 52.8 to 3100 μg m^–3 (6.8 to 400 ppbv) with a sampling time of 60 min. The proposed method has been applied to 2,4-TDI determination in an artificially generated dynamic standard atmosphere, yielding an approximate method detection limit (MDL) of 2 μg m^–3 (0.25 ppbv). This concentration is one twentieth of the Occupational Safety and Health Administration (OSHA) 8-hour time-weighted average (TWA) exposure limit. The sampler with the PDMS–DVB-DBA coating was found to be stable and retains the required amount of DBA for at least 10 days, an important feature for sampling systems with potential in-situ applications. Received: 2 October 2000 / Revised: 4 December 2000 / Accepted: 6 December 2000     

Methylmercury determination in biota by solid-phase microextraction matrix effect evaluation

Aqueous-phase alkylation followed by, headspace solid-phase microextraction (SPME) for mercury speciation in biota, was developed a decade ago. Despite this, matrix effects in this technique have not yet been addressed. In this paper, the importance of these effects has been assessed and overcome by standard addition calibration. Furthermore, improvements were made in the extraction of methylmercury (MeHg) from biological matrixes by optimizing the matrix digestion procedure (temperature and digestion time) and the SPME parameters (aliquot volume of digested samples, extraction temperature and fibre coating), which aimed to minimize the matrix effects. Accordingly, samples were alkaline digested (KOH, 25%, w/v, 60 degrees C, 180 min) and an aliquot was propylated using an aqueous NaBPr(4) solution, headspace SPME sampling and, finally, by using GC-pyrolysis (Py)-atomic fluorescence spectrometry (AFS) determination. The procedure developed was validated using dogfish muscle reference material NRCC DORM-2.     

A new optimization strategy for gaseous phase sampling by an internally cooled solid-phase microextraction technique

This study describes a new optimization strategy for internally cooled solid-phase microextraction based on a multivariate approach. The coating temperature was changed in an extraction while manipulating the extraction times to improve the extraction of compounds with different volatilities. Polycyclic aromatic hydrocarbons (PAHs) and phthalic acid esters (PEs) and adipate were used as model compounds in this study. The optimization strategy was in two steps: (1) multivariate optimization of extraction time and initial coating temperature and (2) multivariate optimization of total extraction time and the time required to cool the coating to a lower temperature as determined in step 1. The observed analytical response in relation to the coating temperature was found to be dependent on the analyte volatility and size. The optimized extraction condition for PEs was 23 min extraction while maintaining the coating at 140°C, followed by 7 min of cooling the coating at 10°C. For the PAHs the coating temperature was maintained at 60°C for the first 20 min and at 5°C in the last 20 min of extraction. Comparisons have been made between the proposed optimized conditions with the conventional internally cooled fiber approach and the results thoroughly discussed. The proposed optimization strategy was found to be more effective for all the analytes, especially for the semi-volatiles, compared to the conventional method.