Surface characterization of commercial fibers for solid-phase microextraction and related problems in their application

The surfaces of commercially available polydimethylsiloxane (PDMS) and Carboxen-PDMS fibers for solid-phase microextraction (SPME) were investigated by optical and electron microscopy. Damage to the coating as well as contamination of new fibers and a highly variable number of pores in Carboxen-PDMS coatings were observed. Together with the contamination of the fibers during their use with metallic particles originating from the SPME fiber holder they are possible explanations for the problems encountered in the analysis of organolead, organotin and organosulfur compounds, such as artifact formation and low repeatability.     

Competitive extraction of multi-component contaminants in water by Carboxen-polydimethylsiloxane fiber during solid-phase microextraction

A headspace analysis for groundwater contaminated with BTEX (benzene, toluene, ethylbenzene, and xylenes) was employed to investigate the feasibility and limitations of Carboxen-PDMS (polydimethylsiloxane) fiber during SPME (solid-phase microextraction). Although the response of the Carboxen-PDMS fiber was much higher than that of conventional PDMS fiber, a reduction of the extracted amount was also observed under multi-component conditions due to competitive replacement. The general affinity of analytes to the fiber was high in the order xylene>ethylbenzene>toluene> benzene. The behavior of the Carboxen-PDMS fiber was examined more precisely at constant compositional ratio, because the analysis of contaminants using Carboxen-PDMS fiber was reported to be possible at known composition. The relative affinity of each component was shown to differ according to the total amount of analytes. Furthermore, the extracted amounts of benzene and toluene did not show a consistent tendency as the concentration of each component increased. These results indicate that caution should be exercised if Carboxen-PDMS fibers are used for the analysis of BTEX in groundwater samples.     

Solid phase microextraction of volatile organic compounds using carboxen-polydimethylsiloxane fibers

Summary A new 80 μm Carboxen-polydimethylsiloxane (PDMS) fiber for solid phase microextraction (SPME) was tested for the enrichment of volatile organic compounds from water and air. Detection limits between 13 ng L⁻¹ (CH₂Cl₂) and 0.1 ng L⁻¹ (CHCl₂Br and CHClBr₂) for the combination: Carboxen-PDMS fiber and GC-ECD and between 35 ng L⁻¹ and 45 ng L⁻¹ (BTEX compounds) for the combination: Carboxen-PDMS and GC-FID using the headspace procedure were determined. Comparisons with the 100 μm PDMS fiber and further coatings show the advantages of the Carboxen-PDMS fiber with respect to extraction efficiency. Disadvantages of the new fiber compared with the 100 μm PDMS fiber are poorer repeatability and prolongation of equilibrium time. Distribution coefficients of the BTEX compounds between aqueous solution and SPME fiber coating were calculated and compared with the results of other researchers and with octanol-water partition coefficients.     

Determination of polar pesticides in soil by solid phase microextraction coupled to high-performance liquid chromatography-electrospray/mass spectrometry

The determination of carbamate and triazine pesticides from soil leachates and slurries was investigated using solid phase microextraction (SPME) coupled to high-performance liquid chromatography-electrospray/ mass spectrometry (HPLC-ESI/MS). SPME was carried out using fibres with a newly developed 50 μm Carbowax/ template coating which are suitable for relatively polar analytes. These fibers exhibit precisions better than 10% RSD, and are resistant against high contents of organic solvents during desorption. The technique shows a high sampling frequency resulting in an increasing sample throughput. Received: 17 December 1997 / Revised: 30 October 1998 / Accepted: 10 November 1998     

Optimization of the SPME device design for field applications

Solid Phase Microextraction (SPME) is a powerful tool for field investigations. With the help of a portable gas chromatograph it can be used for fast analysis directly on-site, or it can be utilized for field sampling and then transported to the laboratory for instrumental analysis. In the latter case, it is important for the reliability of the results that losses of volatiles and contamination of the fiber during storage and transport are minimized. A number of dedicated devices, designed and built for SPME field sampling and storage, have been developed and tested. Sealing capacity of the prototypes was investigated by storing compounds ranging in volatility from methylene chloride to 1,3-dichlorobenzene on selected SPME fibers (100 μm PDMS, 65 μm PDMS/DVB and 75 μm Carboxen/PDMS) at different temperatures. Significant differences were noticed in storage capacity from coating to coating. A comparison between the field samplers optimized in this study and the field sampler commercially available from Supelco revealed advantages and limitations of each of the designs. A gas-tight valve syringe (50 μL SampleLock by Hamilton), modified in order to accommodate the SPME fiber, had the best storage capacity for very volatile compounds. With this device, over 80% of the initial amount of methylene chloride was retained by the 100 μm PDMS fiber after 24 h of refrigerated storage, which is a very good result considering that the PDMS coating is characterized by very low storage capacity for volatiles. Field sampling investigations with the SPME prototypes confirmed the usefulness of these devices for field analysis. Received: 9 November 1998 / Accepted: 15 January 1999     

Optimization of the SPME device design for field applications

Solid Phase Microextraction (SPME) is a powerful tool for field investigations. With the help of a portable gas chromatograph it can be used for fast analysis directly on-site, or it can be utilized for field sampling and then transported to the laboratory for instrumental analysis. In the latter case, it is important for the reliability of the results that losses of volatiles and contamination of the fiber during storage and transport are minimized. A number of dedicated devices, designed and built for SPME field sampling and storage, have been developed and tested. Sealing capacity of the prototypes was investigated by storing compounds ranging in volatility from methylene chloride to 1,3-dichlorobenzene on selected SPME fibers (100 μm PDMS, 65 μm PDMS/DVB and 75 μm Carboxen/PDMS) at different temperatures. Significant differences were noticed in storage capacity from coating to coating. A comparison between the field samplers optimized in this study and the field sampler commercially available from Supelco revealed advantages and limitations of each of the designs. A gas-tight valve syringe (50 μL SampleLock by Hamilton), modified in order to accommodate the SPME fiber, had the best storage capacity for very volatile compounds. With this device, over 80% of the initial amount of methylene chloride was retained by the 100 μm PDMS fiber after 24 h of refrigerated storage, which is a very good result considering that the PDMS coating is characterized by very low storage capacity for volatiles. Field sampling investigations with the SPME prototypes confirmed the usefulness of these devices for field analysis. Received: 9 November 1998 / Accepted: 15 January 1999     

Solid-phase microextraction/capillary gas chromatography for the profiling of confiscated ecstacy and amphetamine

Summary Impurity profiling of ecstacy and amphetamine seizures was accomplished by solid-phase microextraction (SPME) combined with capillary gas chromatography (GC). Samples were dissolved in 0.1 M aqueous acetate buffer (pH 5.0) as the only manual operation and subsequently subjected to SPME-GC. Ecstacy tablets were analyzed by head-space SPME to avoid contamination of SPME fibers with insoluble tablet components, while illicit amphetamine powders were exposed to immersed SPME. A SPME fiber of polydimethylsiloxane-divinylbenzene was found to provide excellent extraction of both polar and non-polar impurities. For both illicit ecstacy and amphetamine, complex impurity profiles were obtained by SPME providing a high information content. For ecstacy, profiles (relative peak areas) were repeatable within 2.2 to 12.6% RSD (n=6) while similar data on amphetamine varied between 2.0 and 10.9% RSD (n=6). No carry-over was observed although each fiber was used for 50 to 100 extractions.     

Use of solid-phase microextraction-capillary-gas chromatography (SPME-CGC) for the varietal characterization of wines by means of chemometrical methods

The extraction of wine aroma compounds was studied by direct-SPME (DI/SPME), headspace-SPME (HS/SPME) and multiple-headspace-extraction-SPME (MHE/SPME). The aromagrams obtained by HS/SPME-CGC were evaluated with chemometrical methods for the varietal classification of wines. Received: 25 July 1997 / Revised: 24 September 1997 / Accepted: 7 October 1997     

Simultaneous analysis of 23 priority volatile compounds in water by solid-phase microextraction–gas chromatography–mass spectrometry and estimation of the method's uncertainty

Most water contaminations with volatile organic compounds (VOCs) are traceable to leaking underground fuel reservoirs, solvent storage vessels, agricultural practices, industrial residues, and deficient wastewater treatment and disposal. In order to perform effective monitoring of such organic micropollutants in a straightforward manner, a multiresidue method for the determination of 23 VOCs (trihalomethanes (THMs), BTEX and chlorinated solvents) in water has been developed using solid-phase microextraction (SPME) and capillary gas chromatography–mass spectrometry (GC–MS). This group includes also methyl-tert-butyl ether, epichlorhydrine, and vinyl chloride which present additional analytical difficulties. Three different fibres were assayed: 7-µm polydimethylsiloxane (PDMS), 100-µm PDMS, and 75-µm Carboxen-PDMS, and the extraction conditions were optimized. The best results for the majority of the analytes and mainly for those with the lowest signals were obtained using the Carboxen-PDMS fibre after 15 min of extraction in the headspace mode at a room temperature of 20 ± 2°C. The analytical sensitivity, linearity, precision, accuracy, and uncertainties have been studied for method validation in agreement with the international standard ISO/IEC 17025:2005. The limits of detection achieved with the proposed method (0.06–0.17 µg L^?1) are adequate to determine the VOCs at the restrictive levels established by the European legislation. This was a decisive achievement to enable the analysis of all VOCs listed under the drinking-water directive in a single assay. The method exhibits performance capabilities suitable for routine analysis of VOCs in drinking-water by quality-control laboratories as enforced by EU Directives. The method is currently being used for this purpose, and participation in proficiency tests was assessed, with encouraging results.     

Solid Phase Microextraction Fibers Coated with Sol-gel Aminopropylsilica/polydimethylsiloxane: Development and Its Application to Screening of Beer Headspace

The preparation and applicability of solid phase microextraction (SPME) fibers coated with a sol-gel organically modified silica based on 3-aminopropyltrimethoxysilane and polydimethylsiloxane (APTMS/PDMS) are described here. Micrographs of the coated fibers revealed a rugous surface; the thickness of the coating was estimated to be less than 30 microm. The APTMS/PDMS fibers were tested with synthetic samples and compared to commercial fibers for headspace SPME analysis of beer. Extraction and desorption using the APTMS/PDMS fibers were faster, which is typical for sol-gel SPME fibers. For polar and semi-polar compounds on beer headspace, the extraction efficiencies of the APTMS/PDMS fiber were superior to those of conventional fibers. The APTMS/PDMS fiber was found to be capable of extracting a broad range of analytes, including highly polar acidic species such as organic acids.     

The preparation, properties and application of carbon fibers for SPME

The conditions of preparation of new types of carbon fibers for solid phase micro extraction (SPME) prepared by methylene chloride pyrolysis (at 600 °C) on the quartz fiber (100 μm) as well as by supporting synthetic active carbon (prepared especially for this purposes) supported in a special epoxide-acrylic polymer is described. The properties of such carbon fibers for SPME were defined by determination of the partition coefficient of the tested substances (i.e., benzene, toluene, xylenes, trichloromethane and tetrachloromethane) and by the microscopic investigations with the application of the optical and scanning electron microscope.

The obtained carbon SPME fibers were applied to the analysis of some volatile organic compounds from its aqueous matrix. During chromatographic GC test, at the investigated SPME carbon fibers, we obtained different but mostly high partition coefficients for the determined compounds (Kfs from 120 for trichloromethane up to 11,500 for tetrachloromethane).

Owing to the high partition coefficients of the studied substances obtained on carbon fibers, it was possible to do the analysis of organic substances occurring in trace amounts in different matrices. In this paper, we present the analysis of BTX contents in the petrol analyzed with the application carbonized with CH₂Cl₂ SPME fiber (C1NM) and a headspace over the petrol sample (concentration of each BTX g/dm³).     

Bonded ionic liquid polymeric material for solid-phase microextraction GC analysis

Four new ionic liquids (IL) were prepared and bonded onto 5-μm silica particles for use as adsorbent in solid-phase microextraction (SPME). Two ILs contained styrene units that allowed for polymerization and higher carbon content of the bonded silica particles. Two polymeric ILs differing by their anion were used to prepare two SPME fibers that were used in both headspace and immersion extractions and compared to commercial fibers. In both sets of experiments, ethyl acetate was used as an internal standard to take into account adsorbent volume differences between the fibers. The polymeric IL fibers are very efficient in headspace SPME for short-chain alcohols. Immersion SPME also can be used with the IL fibers for short-chain alcohols as well as for polar and basic amines that can be extracted at pH 11 without damage to the IL-bonded silica particles. The sensitivities of the two IL fibers differing by the anion were similar. Their efficacy compares favorably to that of commercial fibers for polar analytes. The mechanical strength and durability of the polymeric IL fibers were excellent.      

Determination of linear alkylbenzenesulfonates in communal wastewater by means of solid phase microextraction coupled with API-MS and HPLC-FLD

The use of Solid Phase Microextraction (SPME) for the qualitative and quantitative determination of Linear Alkylbenzenesulfonates (LAS) in waste water samples was investigated. A Carbowax/Templated Resin (CW/?TPR) coated fiber was directly immersed into influent and effluent samples of a sewage treatment plant (STP). Extraction conditions such as time, pH, ion strength were investigated. The extracted LAS were desorbed with a solvent in a specially designed SPME-LC interface for analysis with HPLC-FLD and Electrospray Ionization Mass Spectrometry (ESI-MS). The combination of SPME with ESI-MS proved to be an alternative technique for the LAS determination in waste water. Linear ranges of the external calibration were found from 0.5–100 ng/mL, with detection limits of 0.5 ng/mL for each individual LAS homologue. The reproducibility of the method is 15% (relative standard deviation). Received: 3 May 1999 / Revised: 22 July 1999 / Accepted: 24 July 1999     

Gas chromatography-mass spectrometry method for determining the methanol and acetic acid contents of pectin using headspace solid-phase microextraction and stable isotope dilution

A simple, fast, and direct procedure was developed for the simultaneous determination of the methanol and acetic acid present as esters in the plant cell wall polysaccharide pectin. After base-hydrolysis of esters and acidification of pectin samples, headspace solid-phase microextraction (SPME) was performed using a Carboxen-PDMS fiber assembly. Methanol and acetic acid were separated by gas chromatography with a Chrompak PoraPlot Q capillary column and detected using electron impact mass spectrometry with selected ion monitoring. Stable deuterated isotopomers (d3-methanol and d3-acetic acid) were used as internal standards and for constructing calibration curves, providing accurate and absolute quantification of analytes. The methanol and acetic acid contents in 1 mg quantities of fruit and vegetable pectins were readily quantified by this procedure.     

Potential sources of background contaminants in solid phase extraction and microextraction

A study to identify the sources of background contamination from SPE, using a C-18 sorbent, and solid-phase microextraction (SPME), using a 70 microm carbowax/divinylbenzene (CW/DVB) fiber, was carried out. To determine the source of contamination, each material used in the procedure was isolated and examined for their contribution. The solid-phase column components examined were: sorbent material and frits, column housings and each solvent used to elute analytes off the column. The components examined in the SPME procedure were: SPME fiber, SPME vials, water (HPLC grade), and salt (sodium chloride) used to increase the ionic strength. The majority of the background contaminants from SPE were found to be from the SPE sorbent material and frits. The class of contaminants extracted during a blank extraction were phthalates and other plasticizers used during the manufacturing process. All had blank levels corresponding to measured concentrations below 2 ng/ mL, except for undecane, which had a concentration of 5.4 ng/mL. The most prevalent contaminants in the SPME blank procedure are 1,9-nonanediol, a mixture of phthalates and highly bis-substituted phenols. All the concentrations were below 2 ng/mL, with the exception of bis (2-ethylhexyl) phthalate, which had concentrations ranging from 5 to 20 ng/mL.     

Field air analysis with SPME device

Solid-phase microextraction (SPME) devices were used for a wide scope of air-monitoring including field sampling and analysis of volatile organic compounds (VOCs), formaldehyde, and particulate matter (PM) in air. Grab (instantaneous) and time-weighted average (TWA) sampling were accomplished using exposed and retracted SPME fibers, respectively. Sampling time varied from 1 to 75 min, followed by analysis with a gas chromatograph (GC). A portable GC equipped with unique, in-series detectors: photoionization (PID), flame ionization (FID), and dry electrolytic conductivity (DELCD), provided almost real-time analysis and speciation for common VOCs during an indoor air quality surveys. Indoor air samples collected with SPME devices were compared with those collected using conventional National Institute for Occupational Safety and Health (NIOSH) methods. Air concentrations measured with the SPME device were as low as 700 parts-per-trillion (ppt) for semi-volatile organic compounds. SPME methodology proved to be more sensitive than conventional methods, and provided a simple approach for fast, cost-effective sampling and analysis of common VOCs in indoor air. SPME technology combined with fast portable GC reduced the sampling and analysis time to less than 15 min. The configuration offered the conveniences of immediate on-site monitoring and decision making, that are not possible with conventional methods. In addition, SPME fibers were applied to sampling of particulate matter in diesel engine exhaust. Linear uptake and particulate build-up on the fiber were observed. Preliminary research suggests that SPME fibers could also be applied to sampling of airborne particulate matter.     

葫芦脲用作固相微萃取涂层新材料

本文对葫芦脲(CB)作为一种新型固相微萃取(SPME)涂层材料进行了研究并用于中药白豆蔻的气相色谱分析测定.本文采用的CB SPME涂层制备方法简便、快速,并具有良好的热稳定性和重复性.CB[6]SPME萃取得到的主要成分与水蒸气蒸馏（SD）法基本一致,并且CB[6]SPME对色谱后流出的目标成分的相对峰面积比明显高于SD法和商品SPME萃取材料PDMS/CAR和PDMS/DVB,这可能是由于葫芦脲的特殊分子结构及其与组分分子间选择性作用所致.葫芦脲作为一种新型SPME涂层材料具有很大的研究潜力和应用前景.     

顶空固相微萃取-气相色谱法测定生活饮用水中痕量1,4-二氧六环

建立了生活饮用水中痕量1,4-二氧六环的顶空固相微萃取(HS/SPME)-气相色谱测定方法。考察并优化了萃取头、萃取温度、萃取时间、pH值、样品量、色谱条件等参数。结果表明:提取效率较好的方法是3 mL水样中加入3 mL 600 g/L氢氧化钠溶液,用85 μm Carboxen-PDMS萃取头萃取,用键合碱改性的大口径、厚液膜PTA-5毛细管色谱柱测定。1,4-二氧六环在0.50~50.0 μg/L范围内线性关系良好,相关系数为0.9995;方法检出限(以S/N>3计)为0.14 μg/L;相对标准偏差为2.1%~4.5% (n=6);对实际样品中进行线性范围内的高、中、低3个加标水平的测定,回收率为95.5%~107%,相对标准偏差为1.1%~5.3% (n=6)。建立的方法简便、准确、重现性好、灵敏度高,适合生活饮用水中痕量1,4-二氧六环的常规监测。     

Characterization of volatile effluents of livestock buildings by solid-phase microextraction

This article presents two examples of the application of SPME to the characterisation of gaseous effluents from animal sheds. In the first example the volatile fraction of swine manure was analysed by solid-phase microextraction combined with gas-phase chromatography-mass spectrometry (SPME-GC-MS). To find the best extraction conditions for volatile components, six types of SPME fibre were tested. Carboxen-PDMS fibre performed best, enabling us to extract and identify 101 compounds of varying polarity and molecular weight. The second example shows that it is possible to concentrate the volatile components in various animal shed atmospheres by simple exposure of a fibre inside the building. Direct injection into a mass spectrometer ionisation source (SPME-MS) of the volatile components thus trapped provided signatures characteristic of the four different animal shed atmospheres studied. The practical simplicity of the SPME-MS method makes it a good candidate for rapid identification and monitoring of animal shed atmospheres.     

Determination of phthalates in water using fiber introduction mass spectrometry

Fiber introduction mass spectrometry (FIMS)-a direct coupling of SPME and MS-using selective ion monitoring (SIM) was used to detect and quantify dimethylphthalate (DMP), diethylphthalate (DEP) and dipropylphthalate (DPP) in mineral water. In FIMS, a chromatographic silicone septum is the only barrier between ambient and the high-vacuum mass spectrometer, permitting direct introduction of the SPME fiber into the ionization region of the equipment. After their thermal desorption and ionization and dissociation, the extracted phthalates are detected and quantitated by MS. Three types of SPME fibers were screened for best analyte sorption/desorption behaviors: 100 microm polydimethylsiloxane (PDMS), 65 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) and 65 microm Carbowax/divinylbenzene (CW/DVB). The PDMS/DVB and CW/DVB fibers were then evaluated for precision, and quantitative figures of merit were assessed for extractions using the PDMS/DVB fiber, which displayed the best overall performance. FIMS with the PDMS/DVB fiber allows simple extraction and MS detection and quantitation of DMP in water with good linearity and precision, and at concentrations as low as 3.6 microg L(-1). The LD and LQ of FIMS are below the maximum phthalate concentration allowed by the USEPA for drinking water (6 microg L(-1)).