Microextractions solid-phase

Microencapsulation technique, 13 276-277 Microetching techniques, 19 167 Microextraction, solid-phase, 11 518 Microfermenters, 11 14 Microfibers, 11 186, 240 24 613 Microfibrils, 10 283 11 171 Microfilaments, liquid crystal properties in, 15 111-112... 

SPDE tubular microextraction Solid-phase dynamic extraction with sol-gel coating of more polar analytes... 

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. 

Solid-Phase Microextraction Solid-phase microextraction (SPME) is a preconcentration technique based on the sorption of analytes present in a liquid phase or, more often, in a headspace gaseous phase, on a microbber coated with a chromatographic sorbent and incorporated in a microsyringe [15]. The analytes sorbed in the coating are transferred to a GC injector for thermal desorption. 

Ferreira, V., Sharman, M., Cacho, J.F. and Dennis, J. (1996) New and efficient microextraction/solid-phase extraction method for the gas chromatographic analysis of wine volatiles,/. Chromatogr. A, 731, 247-259. 

This chapter will describe two approaches to microextraction solid-phase extraction (SPE) and solid-phase microextraction (SPME). It is not a comprehensive review. Rather certain key elements of each approach and how it interfaces to the separations step will be described. As SPE is more intuitively understood, and SPME perhaps less so, there is a focus on SPME. SPME has been reviewed from several different perspectives. ... 

Single-Drop Microextraction SOLID-PHASE EXTRACTION... 

Solid-phase microextractions also have been developed. In one approach, a fused silica fiber is placed inside a syringe needle. The fiber, which is coated with a thin organic film, such as poly(dimethyl siloxane), is lowered into the sample by depressing a plunger and exposed to the sample for a predetermined time. The fiber is then withdrawn into the needle and transferred to a gas chromatograph for analysis. 

Caffeine is extracted from beverages by a solid-phase microextraction using an uncoated fused silica fiber. The fiber is suspended in the sample for 5 min and the sample stirred to assist the mass transfer of analyte to the fiber. Immediately after removing the fiber from the sample it is transferred to the gas chromatograph s injection port where the analyte is thermally desorbed. Quantitation is accomplished by using a C3 caffeine solution as an internal standard. 

Pawliszyn, J. Solid-Phase Microextraction Theory and Practice, Wiley NewYork, 1997. 

Schematic diagram of a device for solid-phase microextractions.

Caffeine in coffee, tea, and soda is determined by a solid-phase microextraction using an uncoated silica fiber, followed by a GC analysis using a capillary SPB-5 column with an MS detector. Standard solutions are spiked with G3 caffeine as an internal standard. 

Solid-phase microextraction (SPME) was used for headspace sampling. The FFA were extracted from the headspace with PA, Car/PDMS, and CW/DVB fibers. It was examined whether addition of salt (NaCl) and decreasing the pH by addition of sulphuric acid (H SO ) increased the sensitivity. FFA were analyzed using gas chromatography coupled to mass spectrometry in selected ion monitoring. 

In recent decades the development of preconcentration steps to be implemented prior to analytical determinations of trace level compounds has been explored in considerable depth. With a view to eliminating or at least minimising the use of organic solvents used in conventional liquid-liquid extraction, other methodologies have been developed, such as membrane extraction, solid-phase extraction, solid-phase microextraction, etc. 

SOLID-PHASE MICROEXTRACTION COUPLED WITH GAS OR LIQUID CHROMATOGRAPHY... 

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... 

Figure 11.14 Analysis of amphetamines by GC-NPD following HS-SPME exti action from human hair (a) Normal hair (b) normal hair after addition of amphetamine (1.5 ng) and methamphetamine (16.1 ng) (c) hair of an amphetamine abuser. Peak identification is as follows 1, a-phenethylamine (internal standard) 2, amphetamine 3, methamphetamine 4, N-propyl-/3-phenethyamine (internal standard). Reprinted from Journal of Chronatography, B 707,1. Koide et ai, Determination of amphetamine and methamphetamine in human hair by headspace solid-phase microextraction and gas cliromatography with niti ogen-phosphoms detection, pp. 99 -104, copyright 1998, with permission from Elsevier Science.

S. Ulrich and J. Maitens, Solid-phase microextraction with capillai y gas-liquid cliro-matography and niti ogen-phosphoi us selective detection foi the assay of antidepressant drugs in human plasma , J. Chromatogr. B 696 217-234 (1997). 

J. Pawliszyn, Applications of Solid Phase Microextraction, Royal Society of Chemistry, Cambridge, UK (1999). 

A recent method, still in development, for determining total 4-nitrophenol in the urine of persons exposed to methyl parathion is based on solid phase microextraction (SPME) and GC/MS previously, the method... 

A recent method, still in development, for determining total 4-nitrophenol in the urine of persons exposed to methyl parathion is based on solid phase microextraction (SPME) and GC/MS previously, the method has been used in the analysis of food and environmental samples (Guidotti et al. 1999). The method uses a solid phase microextraction fiber, is inserted into the urine sample that has been hydrolyzed with HCl at 50° C prior to mixing with distilled water and NaCl and then stirred (1,000 rpm). The fiber is left in the liquid for 30 minutes until a partitioning equilibrium is achieved, and then placed into the GC injector port to desorb. The method shows promise for use in determining exposures at low doses, as it is very sensitive. There is a need for additional development of this method, as the measurement of acetylcholinesterase, the enzyme inhibited by exposure to organophosphates such as methyl parathion, is not an effective indicator of low-dose exposures. 

Magdic S, Pawliszyn JB. 1996. Analysis of organochlorine pesticides using solid-phase microextraction. J Chromatogr A723(l) lll-122. 

Lu, G. et al.. Quantitative determination of geosmin in red beets (Beta vulgaris L.) using headspace solid-phase microextraction, J. Agric. Food Chem., 51, 1021, 2003. 

Shen, S. et al.. Comparison of solid-phase microextraction, supercritical fluid extraction, steam distillation, and solvent extraction techniques for analysis of volatile consituents in Fructus amomi, J. AOAC Int., 88, 418, 2005. 

Pretreatment of hair samples also includes an extraction, usually with an alkaline sodium hydroxide solution, followed by cleaning up with LLE with n-hexane/ethyl acetate. Instead of LLE, the employment of SPE is also possible. Furthermore, the solid phase microextraction (SPME) in combination with head-space analysis is usable [104-106]. In the case of using hair samples, possible external contamination (e.g., by passive smoking of Cannabis) has to be considered as false positive result. False positive results can be avoided by washing of the hair samples previous to extraction [107]. Storage of collected samples is another important fact that can cause false results in their content of A9-THC and metabolites [108-110]. 

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