Solid-phase microextraction aqueous samples

Although solid-phase microextraction (SPME) has only been introduced comparatively recently (134), it has already generated much interest and popularity. SPME is based on the equilibrium between an aqueous sample and a stationary phase coated on a fibre that is mounted in a syringe-like protective holder. Eor extraction, the fibre... 

Solid-phase microextraction (SPME) consists of dipping a fiber into an aqueous sample to adsorb the analytes followed by thermal desorption into the carrier stream for GC, or, if the analytes are thermally labile, they can be desorbed into the mobile phase for LC. Examples of commercially available fibers include 100-qm PDMS, 65-qm Carbowax-divinylbenzene (CW-DVB), 75-qm Carboxen-polydimethylsiloxane (CX-PDMS), and 85-qm polyacrylate, the last being more suitable for the determination of triazines. The LCDs can be as low as 0.1 qgL Since the quantity of analyte adsorbed on the fiber is based on equilibrium rather than extraction, procedural recovery cannot be assessed on the basis of percentage extraction. The robustness and sensitivity of the technique were demonstrated in an inter-laboratory validation study for several parent triazines and DEA and DIA. A 65-qm CW-DVB fiber was employed for analyte adsorption followed by desorption into the injection port (split/splitless) of a gas chromatograph. The sample was adjusted to neutral pH, and sodium chloride was added to obtain a concentration of 0.3 g During continuous... 

Solid-phase microextraction (SPME) is also a useful alternative to conventional sample cleanup with LLE or SPE. SPME is based on the enrichment of analytes by a partitioning process between a polymeric phase coated on a fused-silica fiber and its surrounding aqueous solution. SPME combines sample preparation in terms of extraction from a matrix of interfering compounds with an enrichment process in a single step. A method for the determination of metazachlor in wastewater samples is described in the literature [34]. In this study, SPME was shown to be a suitable and simple sample preparation method for the determination of metazachlor in wastewater by GC-AED. 

In the past two decades quite a few new techniques have emerged for the treatment of aqueous samples prior to organic analysis. Perhaps the most important development is that of solid-phase extraction (SPE), which has successfully replaced many off-line steps. This technique can be considered to have introduced a genuine new era in sample handling [1]. The many varieties in which the technique is available and can be applied have made it the key step in handling of aqueous samples. Among the successful varieties are solid-phase microextraction (SPME), matrix solid-phase dispersion, disk extraction and immunosorbent extraction. Several reviews covering these topics have appeared in the literature in the past decade (see e.g. Refs. [2,3] for nonylphenol... 

Isotope fractionation between the vapor phase and the dissolved aqueous phase has been studied only for toluene and trichloroethylene (carbon only [545, 690]). Fractionation associated with adsorption has been quantified only for toluene in regard to sample extraction using a poly(dimethylsilo-xane)-coated solid-phase microextraction fiber [373] and qualified for benzene, toluene, and ethylbenzene based on high-pressure liquid chromatography analyses of isotopically labeled and unlabeled compounds (carbon and hydrogen [692]). Isotope fractionation associated with the reductive dechlorination of chlorinated ethylenes by zero-valent iron and zinc has been... 

Another relatively new SPE approach originally developed for the analysis of volatile organic compounds in environmental samples is solid-phase microextraction (SPME). This technique has gained acceptance for a wide variety of additional applications for the isolation of organic compounds from aqueous solu-... 

Solid-phase microextraction (SPME). used as a sample introduction technique for high speed gc, utilizes small-diameter fused-silica fibers coated with polymeric stationary phase for sample extraction and concentration. SPME lias been utilized for determination of pollutants in aqueous solution by the adsorption of analyte onto stationary-phase coated fuscd-silica fibers, followed by thermal desorption in the injection system of a capillary gas chromatograph. Full automation can be achieved using an autosampler. 

Aqueous samples are extracted with hexane or with methylene chloride by liquid-liquid extraction using a separatory funnel or a mechanical shaker, or by microextraction. Aqueous samples can also be extracted by solid phase extraction using a C-18 cartridge. Selection of sample volume should be based on the extent of sample concentration that may be needed to achieve the required detection level in the analysis, as well as the use of packed or capillary column. A larger sample concentration is required for packed column than that for capillary column analysis. U.S. EPA recommends the extraction of 1 L sample to a final volume of 1 mL for wastewater analysis performed on a packed column. For the analysis of potable water by GC-ECD on a capillary column, concentration of a 35-mL... 

Stir bar sorptive extraction (SBSE), an approach theoretically similar to SPME, was recently introduced [141] for the trace enrichment of organic compounds from aqueous food, biological, and environmental samples. A stir bar is coated with a sorbent and immersed in the sample to extract the analyte from solution. To date, reported SBSE procedures were not usually operated as exhaustive extraction procedures however, SBSE has a greater capacity for quantitative extraction than SPME. The sample is typically stirred with the coated stir bar for a specified time, usually for less than 60 minutes, depending on the sample volume and the stirring speed, to approach equilibrium. SBSE improves on the low concentration capability of in-sample solid-phase microextraction (IS-SPME). 

Solid-phase microextraction (SPME) — is a procedure originally developed for sample preconcentration in gas chromatography (GC). In this procedure a small-diameter fused silica optical fiber, coated with a liquid polymer phase such as poly(dimethylsiloxane), is immersed in an aqueous sample solution. The -> analytes partition into the polymer phase and are then thermally desorbed in the GC injector on the column. The same polymer coating is used as a stationary phase of capillary GC columns. The extraction is a non-exhaustive liquid-liquid extraction with the convenience that the organic phase is attached to the fiber. This fiber is contained in a syringe, which protects it and simplifies introduction of the fiber into a GC injector. Both uncoated and coated fibers with films of different GC stationary phases can be used. SPME can be successfully applied to the analysis of volatile chlorinated organic compounds, such as chlorinated organic solvents and substituted benzenes as well as nonvolatile chlorinated biphenyls. 

Calibration is carried out using standard calibration curves. The simplicity, repeatability, and low cost of the method have allowed its use for routine determination of trihalomethanes in tap water. SOME has also been compared with solid phase microextraction (SPME), purge and trap (P T), and direct aqueous injection (DAI) [10]. This technique offers accuracy comparable with that obtained using P T and DAI. With respect to conventional LEE, the SDME method is more accurate. In contrast to DAI and P T, it requires no special equipment. SDME has been used for extraction of chlorophenols [II], pesticides [12, 13], warfare agents [14], and butanone derivatives [15], and for control of food products [16]. The low costs of the SDME method (typical GC syringe and 2-3 pL of solvent), simplicity, and short extraction time (approximately 15 min) make it particularly suitable for preliminary analyses of organic pollutants in water samples. It can also be an effective alternative to SPME, as it does not require the use of expensive instrumentation. 

Solid Phase MicroExtraction (SPME) is a solvent-free sample preparation method based on the adsorption of analytes directly from an aqueous sample onto a coated fused-silica fiber. Headspace SPME was used in combination with gas chromatography-mass spectrometry/ selective ion monitoring (GC/MS-SIM) to analyze for TCA in wine. 

Nilsson, T, Ferrari, R., and Facchetti, S., Interlaboratory Studies for the Validation of Solid-phase Microextraction for the Quantitative Analysis of Volatile Organic Compounds in Aqueous Samples, Analytica Chimica Acta 356,1997, 113-123. 

For many of these sample preparation tasks, various types of extraction (phase-transfer) procedures are used, such as classical liquid-liquid extraction (LLE) [13-15] in different physical formats, solid-phase extraction (SPE) [16-18], solid-phase microextraction (SPME) [19,20], and other, when studying aqueous and other liquid samples. For solid samples, the classical technique is Soxhlet extraction, and there are a number of modem alternatives [21]. 

A related technique, called solid-phase microextraction, uses a fused silica fiber coated with a nonvolatile polymer to extract organic analytes directly from aqueous samples or from the headspace above the samples. The analyte partitions between the fiber and the liquid phase. The analytes are then desorbed thermally in the heated injector of a gas chromatograph (see Chapter 31). The extracting fiber is mounted in a holder that is much like an ordinary syringe. This technique combines sampling and sample preconcentration in a single step. 

Solid-phase microextraction (SPME) A sample preparation technique that uses a fused silica fibre coated with a polymeric phase to sample either an aqueous solution or the headspace above a sample. Analytes are absorbed by the polymer coating and the SPME fibre is directly transferred to a GC injector or special HPLC injector for desorption and analysis. 

The focus in Chapters 7 and 8 is on the specific sample preparation approaches available for the extraction of organic compounds from environmental matrices, principally soil and water. Chapter 7 is concerned with the role of Soxhlet, ultrasonic and shake-flask extraction on the removal of organic compounds from solid (soil) matrices. These techniques are contrasted with newer developments in sample preparation for organic compound extraction, namely supercritical fluid extraction, microwave-assisted extraction and pressurized fluid extraction. Chapter 8 is arranged in a similar manner. Initially, details are provided on the use of solvent extraction for organic compounds removal from aqueous samples. This is followed by descriptions of the newer approaches, namely solid-phase extraction and solid-phase microextraction. 

Solid-phase microextraction (SPME) is a technique that was first reported by Louch et al. in 1991 (35). This is a sample preparation technique that has been applied to trace analysis methods such as the analysis of flavor components, residual solvents, pesticides, leaching packaging components, or any other volatile organic compounds. It is limited to gas chromatography methods because the sample must be desorbed by thermal means. A fused silica fiber that was previously coated with a liquid polymer film is exposed to an aqueous sample. After adsorption of the analyte onto the coated fiber is allowed to come to equilibrium, the fiber is withdrawn from the sample and placed directly into the heated injection port of a gas chromatograph. The heat causes desorption of the analyte and other components from the fiber and the mixture is quantitatively or qualitatively analyzed by GC. This preparation technique allows for selective and solventless GC injections. Selectivity and time to equilibration can be altered by changing the characteristics of the film coat. 

To improve detection of isotope composition in samples with concentrations < 5 mg other techniques have been employed. For example, headspace solid-phase microextraction (HS-SPME) has determined 5 C [37,41] and 5 H [37] of MTBE in aqueous samples, reaching up to one order of magnitude lower detection limits (11 pg L ) for carbon mode [41]. For hydrogen isotope analysis, concentrations down to 1 mg L have been measured [37]. The small isotopic fractionations caused by these extraction techniques were evaluated by Zwank et al. [42] and were negligible and highly reproducible. 

Abalos, M. and Bayona, J. M., Application of GC coupled to chemical ionisation mass spectrometry following headspace solid-phase microextraction for the determination of free volatile fatty acids in aqueous samples, J. Chromatogr. A, 891, 287-294, 2000. 

Shu, Y. Y., Wang, S. S., Tardif, M., and Huang, Y., Analysis of PCBs in aqueous samples by microwave-assisted headspace solid-phase microextraction, J. Chromatogr. A, 1008, 1-12, 2003. 

The newly developed solid-phase microextraction (SPME) technique, first reported by Pawliszyn in 1989, is increasingly used for the gas chromatographic determination of a wide variety of volatile and semivolatile organic compounds in water or aqueous extracts of different substrates. Basically, it involves the extraction of specific organic analytes directly from aqueous samples or from the headspace of these samples in closed vials. The extraction is achieved onto a fused-silica fiber coated with a polymeric liquid phase. After equilibration, the fiber containing the absorbed or adsorbed analyte is removed and thermally desorbed in the hot injector port of a gas chromatograph or in an appropriate interface of a liquid chromatograph. ... 

Direct sample introduction without any derivatization is used as an alternative to derivatization and is most commonly applied to VFA. GC introduction techniques include direct aqueous and solvent injections, ° " ° headspace, and more recently solid-phase microextraction (SPME) Specially designed capillary GC columns with polar phases are typically followed... 

Greaser, C. S., Weston, D. J., Wilkins, J. P. G., Yorke, C. P., Irwin, J., and Smith, B., Determination of benzene in aqueous samples by membrane inlet, solid-phase microextraction and purge and trap extraction with isotope dilution gas chromatography-mass spectrometry. Anal. Commun., 36(11-12), 383-386, 1999. 

Menendez, J. C. F., Sanchez, M. L. F., Uria, J. E. S., Martinez, E. F., and Sanz Medel, A., Static headspace, solid phase microextarction and headspace solid-phase microextraction for BTEX determination in aqueous samples. Anal. Chim. Acta, 415(1-2), 9-20, 2000. 

Nilsson, T., Baglio, D., Galdo-Miguez, I., 0gaard Madsen, J., and Facchetti, S., Dramatization/solid-phase microextraction followed by gas chromatography-mass spectrometry for the analysis of phenoxy acid herbicides in aqueous samples, J. Chromatogr. A, 826, 211-216, 1998. 

Aguilar, C., Penalver, S., Pocurull, E., Borrull, F., and Marce, R. M., Solid-phase microextraction and gas chromatography with mass spectrometric detection for the determination of pesticides in aqueous samples, J. Chromatogr. A, 795, 105-115, 1998. 

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