Solid-phase microextraction device

Bartelt, R.J. Calibration of a commercial solid-phase microextraction device for measnring headspace concentrations of organic volatiles. Anal. Chem., 69(3) 364-372, 1997. 

Guzman, N. A., Improved solid-phase microextraction device for use in on-line immunoaffinity capillary electrophoresis. Electrophoresis 24(21), 3718-3727, 2003. 

Ouyang, G., Y. Chen, and J. Pawliszyn. 2005. Time-weighted average water sampling with a solid-phase microextraction device. Anal. Chem. 77 7319-7325. 

Figure 8.11 Schematic of a solid-phase microextraction device. Reprinted with permission from Zhang, Z., Yang, M. and Pawliszyn, J., Anal. Chem., 66, 844A-853A (1994). Copyright (1994) American Chemical Society.

A set of 25 barbiturates was analyzed using CZE and MEKC. Buffers consisting of 90 mM borate, pH 8.4 (CZE), and 20 mM phosphate, 50 mM sodium dodecylsulfate (SDS), pH 7.5 (MEKC). The methods were evaluated for their suitability in systematic toxicological analysis (STA), especially when a combination of methods having a low correlation is used (305). A solid-phase microextraction device in combination with CE for the determination of barbiturates was described (see 306 and Sec. VII). The detection limit for 10 barbiturates was 0.1 ppm in urine, while the limit of detection was about 3 times poorer in bovine serum (306). Polyacrylamide-coated columns have been used for barbiturates and benzodiazepines. Seven kinds of barbiturates were sucessfully separated with the coated columns without further additives (307). The benzodiazepines, which are electrically neutral solutes, were separated in the presence of SDS. The CE method offered fast and efficient separations of the more hydrophobic solutes. 

In headspace analysis, the plastic is placed in a vial (at a raised temperature) and the volatiles formed are stripped by a flow of carrier gas. The stripped volatiles are trapped in a suitable sorbent (e.g., using a solid-phase microextraction device) and subsequently thermally desorbed into a gas chromatograph. Process gas chromatographs are used in industrial analysis of volatiles in plastics. An example of this technique is the determination of residual vinyl chloride monomer in plastics in the range of 5-50 g per kg. With direct injection of a polymer solution, there is a danger of side-effects (a loss of reactive monomers due to polymerization in the injection port or an increase in its content due to depolymerization at a high injection temperature). 

Solid-phase microextraction device. (From Bogialli, S. et al.. Food Toxicants Techniques, Strategies and Developments, ch. 9 Extraction Procedures, 2007, 269-298 edited by Yolanda Pico, Elsevier, Amsterdam. With permission.)... 

The solid-phase microextraction device (SPME) was purchased from Supelco Co. (Bellefonte, PA). The following types of SPME fiber were used polydimethylsiloxane (PDMS) with lOO-pm thickness, PDMS/ divinylbenzene (DVB) with 65-pm thickness, and Carboxen (Supelco Co., Bellefonte, PA, U.S.A.)/PDMS (CAR/PDMS) with 75-pm thickness. 

Schematic diagram of a device for solid-phase microextractions.

The most widely employed techniques for the extraction of water samples for triazine compounds include liquid-liquid extraction (LLE), solid-phase extraction (SPE), and liquid-solid extraction (LSE). Although most reports involving SPE are off-line procedures, there is increasing interest and subsequently increasing numbers of reports regarding on-line SPE, the goal of which is to improve overall productivity and safety. To a lesser extent, solid-phase microextraction (SPME), supercritical fluid extraction (SEE), semi-permeable membrane device (SPMD), and molecularly imprinted polymer (MIP) techniques have been reported. 

Miniaturisation of scientific instruments, following on from size reduction of electronic devices, has recently been hyped up in analytical chemistry (Tables 10.19 and 10.20). Typical examples of miniaturisation in sample preparation techniques are micro liquid-liquid extraction (in-vial extraction), ambient static headspace and disc cartridge SPE, solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE). A main driving force for miniaturisation is the possibility to use MS detection. Also, standard laboratory instrumentation such as GC, HPLC [88] and MS is being miniaturised. Miniaturisation of the LC system is compulsory, because the pressure to decrease solvent usage continues. Quite obviously, compact detectors, such as ECD, LIF, UV (and preferably also MS), are welcome. 

In the 1990s, Pawliszyn [3] developed a rapid, simple, and solvent-free extraction technique termed solid-phase microextraction. In this technique, a fused-silica fiber is coated with a polymer that allows for fast mass transfer—both in the adsorption and desorption of analytes. SPME coupled with GC/MS has been used to detect explosive residues in seawater and sediments from Hawaii [33]. Various fibers coated with carbowax/divinylbenzene, polydimethylsiloxane/divinylbenzene, and polyacrylate are used. The SPME devices are simply immersed into the water samples. The sediment samples are first sonicated with acetonitrile, evaporated, and reconstituted in water, and then sampled by SPME. The device is then inserted into the injection port of the GC/MS system and the analytes thermally desorbed from the fiber. Various... 

S. A. S. Werdnski, ed.. Solid Phase Microextraction A Practical Guide (New York Marcel Dekker, 1999) Z. Zhang, M. J. Yang, and J. Pawliszyn, Solid-Phase Microextraction, Anal. Chem. 1994, 66, 844A P. Mayer, J. Tolls, J. C. M. Hermens, and D. MacKay, Equilibrium Sampling Devices. Environ. Sci. Technol. 2003,37, 185A. 

It is recognized that filtration is operational, that colloidal-bound PCB congeners are not retained by the filter, and that operational dissolved measurements may be biased positively by colloidal material. Techniques to measure truly dissolved PCBs include gas sparging, differential diffusion into membrane-bound lipids (e.g., semipermeable membrane devices, [230]), and selective adsorption (e.g. non-equilibrium solid phase microextraction [231, 232]). Unfortunately, none of these techniques has sufficient sensitivity to reliably and unambiguously measure truly dissolved PCB congeners at the levels present in the Great Lakes. 

Lanno, R., T.W. La Point, J.M. Conder, and J.B. Wells. 2005. Application of solid-phase microextraction fibers as biomimetic sampling devices in ecotoxicology, Chapter 28. In G.K. Ostrander (ed.), Techniques in Aquatic Toxicology, Vol. 2, pp. 511-522. Florida Taylor Francis-CRC Press. 

Solid-phase microextraction (SPME) was developed as an alternative to many other sample preparation methods because it uses virtually no solvents or complicated equipment. It is an adsorption/desorption device where the compounds of interest are adsorbed onto a fused-silica fiber. After a given time, the fiber is placed into a gas chromatograph (GC), where the compounds are thermally desorbed. SPME has recently been adapted for use in HPEC, where compounds that are adsorbed are desorbed using an appropriate solvent. 

Andres, A.I., Cava, R. and Ruiz, J. (2002) Monitoring volatile compounds during dry-cured ham ripening by solid-phase microextraction coupled to a new direct-extraction device,/. Chromatogr. A, 963(1-2), 83-88. 

Sample analysis based on sorption onto SPE sorbents followed by elution with organic solvent is the basis of the majority of SPE methods. However, the use of fibers to sorb organic compounds directly from solution was developed by Pawliszyn and co-workers (Arthur and Pawliszyn, 1990), and devices are commercially available from Supelco (see Chapter 12 for a description of the method). The adsorbed compounds may be directly desorbed into the GC without a solvent peak by simply heating the fiber in the inlet of the gas chromatograph. Solid-phase microextraction (SPHE) has mainly been used... 

Figure 3.12. Schematic diagram of the sample handling device for solid-phase microextraction. (From ref. [139] Wiley-VCH).

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