Stationary-phase-coated fused-silica fiber

SPME has been utilized for determination of pollutants in aqueous solution by the adsorption of analyte onto stationary-phase coated fused-silica fibers, followed by thermal desorption in the injection system of a capillary gas chromatograph (34). Full automation can be achieved using an autosampler. Fiber coated with 7- and 100-JJ.m film thickness and a nitrogen—phosphoms flame thermionic detector were used to evaluate the adsorption and desorption of four j -triazines. The gc peaks resulting from desorption of fibers were shown to be comparable to those obtained using manual injection. 

Fused-silica fiber coated with stationary phase... 

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. 

Fused silica fiber with stationary liquid-phase coating... 

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). 

Solid-Phase Microextraction. 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 (33). The trapped analyte can be liberated by thermal desorption. By using a specially designed dedicated injector, the desorption process can be shortened to a fraction of a second, producing an injection band narrow enough for high speed gc. A modified system has been investigated for the analysis of volatile compounds listed in EPA Method 624. Separation of all 28 compounds by ion trap mass spectrometric detector is achieved in less than 150 seconds. 

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. 

Solid phase micro extraction (SPME) is a widely used extraction technique that was developed by Pawlistyn and co-workers in 1990 (74). SPME uses a fused silica fiber that is coated on the outside with an appropriate stationary phase (a S to 100 pm thick coating of different polymers, e.g. polydimethylsiloxane, PDMS). The small size of the SPME flber and its cylindrical shape enables it to fit inside the needle of a syringe-like device. Target molecules from a gaseous or a liquid sample are extracted and concentrated to the polymeric fiber coating. SPME has been used coupled to GC and GC-MS (75), as well as to HPLC and LC-MS 7ll>). Figure 7 shows a conunercially available SPME device. 

SPME was hrst used by Pawliszyn et al. in 1990. It is a two-step process conductive to the simultaneous extraction and preconcentration of analytes form sample matrices. In the first step, a fused-silica fiber coated with a polymeric stationary phase is exposed to the sample matrix where the analyte partitions between the matrix and the polymeric stationary phase. In the second step, the fiber/analyte is transferred to the analytical instrument for desorption, separation, and quantification. SPME has a number of advantages over traditional extraction techniques for pesticides. In fact, it is fast, simple, solvent-free, and easily automated for both GC and HPLC instruments. It exhibits good linearity and sensitivity. Thus, carbamate and organophosphorus pesticides in golf course samples were successfully extracted by SPME and analyzed by HPLC by Jinno et al. ... 

Solid-phase micro-extraction (SPME) first became available to analytical researchers in 1989. The technique consists of two steps first, a fused-silica fiber coated with a polymeric stationary phase is exposed to the sample matrix where the analyte partitions between the matrix, and the polymeric phase. In the second step, there is thermal desorption of analytes from the fiber into the carrier gas stream of a heated GC injector, then separation and detection. Headspace (HS) and direct insertion (DI) SPME are the two fiber extraction modes, whereas the GC capillary column mode is referred to as in-tube SPME. The thermal desorption in the GC injector facilitates the use of the SPME technology for thermally stable compounds. Otherwise, the thermally labile analytes can be determined by SPME/LC or SPME/GC (e.g., if an in situ derivatization step in the aqueous medium is performed prior to extraction). Different types of commercially-avarlable fibers are now being used for the more selective determination of different classes of compounds 100 /rm polydimethylsiloxane (PDMS), 30 /rm PDMS, 7 /rm PDMS, 65 /rm carbowax-divinylbenzene (CW-DVB), 85 /rm polyacylate (PA), 65 /rm PDMS-DVB, and 75 /rm carboxen-polydimethyl-siloxane (CX-PDMS). PDMS, which is relatively nonpolar, is used most frequently. Since SPME is an equilibrium extraction rather than an exhaustive extraction technique, it is not possible to obtain 100% recoveries of analytes in samples, nor can it be assessed against total extraction. Method validation may thus include a comparison of the results with those obtained using a reference extraction technique on the same analytes in a similar matrix. 

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. 

SPME is a recent sample prep technique for trace analysis by GC [18]. It is a simple, solvent-free method which uses a nonpolar fiber (usually dimethylpolysiloxane) to extract analytes from a polar matrix (usually aqueous). A fused silica fiber is coated with a thin film (7, 30, or 100 /im) of stationary phase. The small size and cylindrical geometry allow easy incorporation of the coated fiber into an ordinary GC syringe. The coated fiber is exposed to the sample matrix or to the headspace, and analytes are adsorbed (extracted) from the sample matrix. After the fiber is removed from the sample, it is transferred to the heated inlet of a GC system and the analytes are thermally desorbed for analysis. The technique works well with trace amounts of nonpolar and semipolar analytes in water. 

Stationary phase, such as plasticized poly vinyl chloride (PVC), " which is coated onto a fused silica fiber. 

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... 

A new technique, which is applicable for sampling in air and liquids or in the headspace above a liquid or a solid sample, is solid-phase micro-extraction (SPME). The mechanism of SPME, which has been developed by Pawliszyn et al. 1225], [226], is based on the partition equilibrium of the analytes between the sample or the head-space above the sample, respectively, and a fused silica fiber coated with a suitable stationary phase. The amount of analyte extracted by the fiber is proportional to the initial analyte concentration in the sample and depends on the type of fiber. After sampling, the fiber can be thermally desorbed directly into the injector of a gas chromatograph. SPME combines sampling, analyte enrichment, matrix separation, and sample introduction within one step [226]. Since its development, this innovative technique has found widespread use in environmental analysis. It has, for example, been applied in the determination of volatile organic compounds [227], 228]. phenols [229],... 

A fused silica fiber coated with an immobilized phase of the above coatings is fixed inside a syringe. For the analysis of aqueous samples, the fiber is exposed to the liquid and the analytes are accumulated in the stationary phase imtil equilibrium is reached. The fiber is then removed from the solution and the extracted organic substances are thermally desorbed in a split-splitless or oncolumn injector of a gas chromatograph or desorbed by organic solvents and injected into HPLC system. As indicated earlier at the beginning of this section, SPME has been successfully coupled with various techniques such as GC, HPLC, CE, and MS [164-168]. 

General considerations SPME is a technique developed about 15 years ago by Arthur and coworkers [21]. The main elements of SPME are fused-silica fibers coated by a polymeric stationary phase. By means of the fibers, the analytes are extracted out from various waters. The method combines isolation and enrichment of investigated substances in one stage. 

The analytes from a liquid or from the headspace above a sample are concentrated on a fused silica fiber coated with a polymer film, causing an equilibrium distribution of the analytes to be established between the stationary phase (the microfiber) and the aqueous or gas phase (the sample). Once equilibrium has been established between sample and fiber, the concentrated compounds are thermally desorbed in the injector of a gas chromatograph and transferred to the capillary column (Eig. 1). The parameters to be optimized here are the nature of the fiber coating (fiber polarity) and fiber film thickness, as well as the concentra-... 

The technique was further improved by employing a polymer coating on the polymeric fibers packed in a fused silica capillary. The coating material was based on GC stationary phases. The polymer-coated fiber-packed capillary was used as the sample loop of the LC injection valve for the extraction of phthalate esters from river water and wastewater.22 The coated-fiber extraction capillaries demonstrated a better extraction efficiency and lower limit of quantification (LOQ) than the uncoated-fiber capillaries. Also, the coated fibers were similarly packed in a PEEK tube, which was used as the injection loop or integrated in the rotor of an LC injection valve employed for the extraction of phthalates. The results clearly showed that an extraction with high selectivity could be established with an appropriate type of polymer coating.23... 

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. 

This method utihzes a fused silica rod coated with a thin layer of stationary phase mounted in a holder. During extraction, the fiber is exposed to the sample, and analytes are adsorbed onto the stationary phase and concentrated. After a defined extraction time, the fiber is withdrawn in the holder and then analytes are thermally desorbed in the GC injector. Several types of coatings are commercially available, such as PDMS, polyamide, Carbowax-DVB, Carboxen-PDMS, and PDMS-DVB. Coatings prepared with three kinds of materials are also available (e.g., DVB-Carboxen-PDMS) [71]. Selection of the fiber is mainly based on the principle like dissolves like. For example, PDMS sorbent is suitable for the extraction of hydrocarbons, and the sorbent should be polar for the extraction of alcohols or ketones. The thickness of the coating film determines the sorption capacity of the fiber. Changing the temperature, pH, or ionic strength of the hquid... 

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... 

SPME is a modified SPE procedure based on the use of a coated fiber made of fused silica. After the extraction the fiber is directly introduced into the injector of the GC instmment to allow the direct transfer of the analytes into the chromatographic column, thus avoiding the use of organic solvents. Chromatographic stationary phases, such as poly(methylsiloxane), are used as chemically bonded coatings of the fiber. SPME is an inexpensive and easily automated technique, but its most important drawbacks are the poor detection limits compared to SPE and the time required for sorption on the fiber. 

The SPME fiber most often consists of fused silica, coated with a polymer (stationary phase), which is bound to a plunger (stainless steel). It is placed inside a hollow needle with a diameter that allows it to move freely in and out. SPME devices resemble to a large extent a microliter syringe. The extraction fiber is moved out and inside the needle using the plunger. 

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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