Stationary-phase microextraction

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... 

Principles and Characteristics Solid-phase microextraction (SPME) is a patented microscale adsorp-tion/desorption technique developed by Pawliszyn et al. [525-531], which represents a recent development in sample preparation and sample concentration. In SPME analytes partition from a sample into a polymeric stationary phase that is thin-coated on a fused-silica rod (typically 1 cm x 100 p,m). Several configurations of SPME have been proposed including fibre, tubing, stirrer/fan, etc. SPME was introduced as a solvent-free sample preparation technique for GC. 

Nitrobenzene, 2,4-dinitrotoluene and 2,6-dinitrotoluene were determined in water by GC-EC or GC-CLD thermal energy analyzer (TEA) and by EI-MS, CI-MS and NICI-MS455, after solid-phase microextraction (SPME) with polydimethylsiloxane coated fiber. SPME is a technique to concentrate organic compounds dissolved in an aqueous matrix by adsorption on a solid stationary phase immobilized on a fused silica fiber. The analytes were thermally desorbed directly into the GC injector LOD was 9 pg/L for nitrobenzene and 15 pg/L for the dinitrotoluenes456. 

Solid-phase microextraction (SPME) is effectively a miniamrised version of SPE. Instead of using a packed cartridge, a rod is typically used, which is coated with the stationary phase. This is dipped into a solution of the analyte and allowed to extract for a pre-determined period of time. After this incubation period, the rod is removed from the solution and may be inserted directly into the injection system of the GC or HPLC. All of these operations can be automated on an autosampler. Clearly, the success of this technique depends intimately on the affinity of the analyte for the stationary phase. Frost, Hussain and Raghani [34] used SPME with GC-FID to measure benzyl chloride and chloroethylmethyl ether (amongst other process impurities) in pharmaceutical preparations. 

The analysis of ILs may afford considerable insight into the physicochemical properties underlying the rich potential interaction chemistries of ILs [14] and suggest possibilities for future applications. Simultaneously, the unique features of ILs provide some intriguing new possibilities in the area of separations that have yet to be realized. Hence, topics to be covered in this chapter include analysis of ILs by LC, applications of ILs in liquid-phase microextraction (LPME), in high-performance LC (HPLC) as mobile-phase additives, and in capillary electrophoresis (CE) as buffer additives as well as applications of surface-confined ILs (SCIL) as novel stationary phases for LC. 

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. 

Solid-phase microextraction uses a 1-cm length of focused silica fiber, coated on the outer surface with a stationary phase and bonded to a stainless steel plunger holder that looks like a modified microliter syringe. The fused-silica fiber can be drawn into a hollow needle by using the plunger. In the first process, the coated fiber is exposed to the sample and the target analytes are extracted from the sample matrix into the coating. The fiber is then transferred to an instrument for desorption. The technique has been promoted by Pawliszyn (69). 

CME Capillary microextraction Fused silica capillary of up to 40 cm coated internally with the stationary phase analyte elution by solvent Suited for on-line SPE-HPLC, for example, with MTMS/ PEO-coated capillary... 

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. 

Headspace solid-phase microextraction (HS-SPME) is a rapid and solvent-free modification of the SPME technique in which a fine fused silica fiber with a polymeric coating is inserted into a headspace gas to extract organic compounds and directly transfer them into the injector of a gas chromatograph for thermal desorption and analysis. In this technique, the quantity of compounds extracted onto the fiber depends on the polarity and thickness of the stationary phase as well as on extraction time and concentration of volatiles in the sample. 

The method is different from conventional SPE in that SPE isolates the majority of the analyte from a sample (> 90%) but only injects about 1 to 2% of the sample onto the GC. Solid-phase microextraction isolates a much smaller quantity of analyte (2-20%), but all of that sample is injected into the GC. The extraction efficiency of the fiber is a combination of extraction time, the thickness of the stationary phase, and the magnitude of the partition coefficient for the stationary phase. 

Solid-phase microextraction (SPME) is a sampling and concentration technique used to increase the sensitivity of HS methods. This technique is utilized for arson analysis and environmental monitoring purposes and also for clinical and forensic procedures. Short, narrow diameter, fused-silica optical fibers coated with stationary phase polymers are either immersed in the sample or the HS and compounds are adsorbed or absorbed (depending on... 

Another useful technique is solid phase microextraction. A fused silica fibre is attached to the base of a syringe with a fixed metal needle. The fibre is coated with a thin layer of stationary phase that is selective for the analytes of interest. The fibre is dipped into the liquid sample or into the headspace above the liquid for a period of time, allowing a fraction of the analyte to be extracted into the fibre. The fibre is then retracted into the syringe and the syringe injected into the injection port where the analyte is thermally desorbed from the fibre into the GC. 

Several techniques have been used to overcome the problem of low column loadings on capillary columns. Capillary columns have been used after preconcentration of the alkylderivatives on a wide-bore fused-silica column or by solid-phase microextraction (SPME). " Large volume injection techniques have been applied on capillary columns coated with 0.25 /rm DB-5. Multicapillary GC (MCGC) (919 capillaries, 1 m X 40/rm i.d. coated with 0.2/rm SE 30 stationary phase (Alltech)) coupled to allows column loadings and carrier gas flow... 

SoHd-phase microextraction (SPME) is currently under investigation in many laboratories for its usefulness for a large variety of bioanalytical applications SPME involves extraction and pre-concentration with a fused silica fibre or tubing coated with a polymeric stationary phase. SPME can be performed in two-phase (sample-fibre coating) and three-phase (sample-headspace-fibre coating) systems [58]. 

Solid-phase microextraction (SPME) is a miniaturized variation of the SPE, based on the partitioning of the analytes between the sample matrix and the stationary phase, which is coated on a fused-silica fiber. SPME with CE has been applied in environmental analysis to determine PAHs in water, and pesticides in vegetables. Trapped analytes can be desorbed by an organic solvent or directly into the CE electrolyte stream, via an adapter. 

Solid phase microextraction (SPME) involves extraction onto a thin fiber and the technique has become more prevalent recently and additionally provides a preconcentration of analytes prior to analysis. The fibers used in the technique can be coated with a range of stationary phases and a nonpolar phase such as polydimethylsiloxane (PDMS) is typically used for the extraction of derivatized organotin species. An equilibrium is established between the sample extract solution (or the headspace above the solution) and the stationary phase coating the fiber. The analytes are then typically desorbed from the fiber for analysis, for example, using thermal desorption during GC analysis. The technique allows rapid and solvent-free extraction of the analytes. Very good extraction has been achieved for water samples however, the technique has been shown to be more variable with more complex matrices. 

While open tubular (OT) columns are the most popular type, both open tubular and packed columns are treated throughout, and their advantages, disadvantages, and applications are contrasted. In addition, special chapters are devoted to each type of column. Chapter 2 introduces the basic instrumentation and Chapter 7 elaborates on detectors. Other chapters cover stationary phases (Chapter 4), qualitative and quantitative analysis (Chapter 8), programmed temperature (Chapter 9), and troubleshooting (Chapter 11). Chapter 10 briefly covers the important special topics of GC-MS, derivatization, chiral analysis, headspace sampling, and solid phase microextraction (SPME) for GC analysis. 

By microextraction to the stationary phase, gases present in the liquid are adsorbed on to a sorbent from which they are thermally desorbed. ... 

Solid-phase microextraction is based on the adsorption of an analyte in a fused-silica fiber externally coated with a stationary phase and following a thermal desorption in the injector of a GC. The fiber is introduced into the aqueous sample. In SPME, usually equilibrium among the aqueous... 

The anion chromatogram of a microextract is depicted in Figure 10.136. Usually, fluoride, chloride, orthophosphate, nitrate, and sulfate are found as anionic contaminants on a reading head. lonPac AS12A in the microbore format has proved to be a suitable stationary phase for separating these anions, which are eluted with a carbonate/bicarbonate eluent mixture. The minimum detection limits for a single reading head obtained with this technique are summarized in Table 10.19. 

Polyclonal antibody Pu e-and-trap Quiescent solution Radioimmimoassay Relative affinity Reversed phase Solid-phase extraction Solid-phase microextraction Solubility Solvent extraction Solvent strength Stationary phase Thin-layer chromatography Titer... 

Solid-phase microextraction (SPME) is a modified SPE procedure based on the use of a fiber, usually made of fused silica, coated with a suitable stationary phase such as poly(methylsiloxane) [13,77,148]. The fiber can be directly immersed in the water sample and maintained under stirring during the preconcentration step. Alternatively SPME fiber can be exposed to the headspace vapor over the water sample [122]. 

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