SPME

SPME consists of two steps extraction and desorption. In the extraction process the fiber is immersed into the sample with a syringe, vigorous stirring is applied, and the organic micropollutants are retained in the fiber depending on their distribution coefficients. Then, using the holder, the fiber is transferred to the analytical instrument for desorption, separation and quantification. The method has been automated and commercial systems are available which will extract, agitate, and inject the sample into a GC system. In HPLC the sample is extracted directly into the eluent stream rather than thermally desorbed.  

In the case of headspace extraction (HS-SPME) a fiber in the needle tip of a gas chromatographic microsyringe is exposed to the headspace above a sample. Volatile compounds are extracted and concentrated in the fiber. Next, the fiber is retracted into the microsyringe and injected directly into the gas chromatograph. This extraction technique has been successfully 

Another possibility is the use of a membrane to protect the hber. This system is used when very complex and dirty samples have to be extracted and headspace SPME can not be applied. 

The advantages of SPME over other classical extraction techniques are  

The drawbacks are that the fiber is fragile and can be damaged by a build-up of nonvolatile materials from the samples the extraction process can be relatively slow because it relies on sufficient stirring or diffusion to bring the analytes into the fiber. 

Solid-phase microextraction (SPME) is a solvent-free sample preparation technique. The volume of the extraction phase is very small compared to the sample volume. The extraction is not exhaustive, but is based on equilibrium between the sample and the extraction phase, which is located on a fiber. SPME involves an adsorption step of the analyte, from a gas headspace or in a liquid sample (direct immersion), and a desorption step, which often is coupled directly with injection in the analytical system. Although SPME is mainly used in combination with GC, it has also been automated for HPLC. Eigure 9.10 shows a schematic representation of an SPME device. 

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. 

Sampling is carried out by penetrating the needle through the septum of a sample vial followed by pushing approximately 1 cm of the fiber outside the needle into the sample. When adsorption equilibrium is obtained, the fiber is withdrawn from the sample and into the needle. Adsorption equilibrium varies from 2 to 30 min. The equilibrium reached can be described as follows  

This is a simplified representation where n is the amount of analyte extracted, Kfs is the distribution coefficient of the analyte between stationary phase and sample, Vf is the volume of the stationary phase, and Q is the start concentration of the analyte in the sample. The sample volume is not of importance in SPME, since it relies on the equilibrium (nonexhaustive) and the fact that the volume of the stationary phase is very small compared to the sample volume. This makes SPME a good sample preparation technique for in the field sampling. Note that the equilibrium is obtained much faster when performing headspace sampling compared to immersion sampling. This is due to the faster movement of the analytes in the gas phase compared to that in the liquid phase. 

In contrast to SPE, the SPME fiber can be reused up to 100 extractions and more, depending on the sample type. 

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Yang, M. J. Orton, M. L. Pawliszyn, J. Quantitative Determination of Caffeine in Beverages Using a Combined SPME-GC/MS Method, /. Chem. Educ. 1997, 74,... 

An attractive approach to isolating analytes is a solid-phase microextraction (SPME). In one approach, which is illustrated in Figure 12.19, a fused silica fiber is placed inside a syringe needle. The fiber, which is coated with a thin organic film, such as polydimethyl siloxane, is lowered into the sample by depressing a plunger and is exposed to the sample for a predetermined time. The fiber is then withdrawn into the needle and transferred to the gas chromatograph for analysis. 

Scrap and Recycle. Acetal resins can be processed with very Htde waste. Spmes, mimers, and out-of-tolerance parts can, in general, be ground and the resins reused. Up to about 25% of regrind can usually be safely recycled into virgin resin. However, the amount of regrind that can be used in a particular circumstance varies. The appropriate Hterature from the suppHer should be consulted. 

Diarrhea is a common problem that is usually self-limiting and of short duration. Increased accumulations of small intestinal and colonic contents are known to be responsible for producing diarrhea. The former may be caused by increased intestinal secretion which may be enterotoxin-induced, eg, cholera and E. col] or hormone and dmg-induced, eg, caffeine, prostaglandins, and laxatives decreased intestinal absorption because of decreased mucosal surface area, mucosal disease, eg, tropical spme, or osmotic deficiency, eg, disaccharidase or lactase deficiency and rapid transit of contents. An increased accumulation of colonic content may be linked to increased colonic secretion owing to hydroxy fatty acid or bile acids, and exudation, eg, inflammatory bowel disease or amebiasis decreased colonic absorption caused by decreased surface area, mucosal disease, and osmotic factors and rapid transit, eg, irritable bowel syndrome. 

Fig. 14. A fliU shot A, spme B, ninner C, gate and D, part.

SPME has been utilized for deterrnination of pollutants in aqueous solution by the adsorption of analyte onto stationary-phase coated fused-siUca fibers, followed by thermal desorption in the injection system of a capillary gas chromatograph (34). EuU automation can be achieved using an autosampler. Eiber coated with 7- and 100-p.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. 

Ingots produced by secondary smelters and refiners and made to specifications are a good source of melting stock. Scrap, such as spmes and gates, and turnings from the foundry s own castings are very acceptable melting materials. 

Arc-melted titanium has excellent fluidity and lends itself readily to the creation of thin margins. Spmes must be carefully placed and abundant venting provided, however, to avoid holes and porosity ia the casting. The detection of defects by radiography is faciUtated by the low density of titanium, and conventional dental x-ray units may be used ia many cases. 

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. 

Different options have been tested to increase the sensitivity of the SPME method. First, the PA fiber had a better sensitivity compared to the other fibers. Second, addition of 10% NaCl and lowering the pH to 1.5 increased the sensitivity with a factor of 10. 

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.

In a recent report, HS-SPME was used for the extraction of amphetamines from human hair (142). Human hair analysis is gaining interest in the analysis of drugs of abuse, since it offers attractive features easy and unlimited sampling, and as the... 

The use of SPME for CE has not (yet) been studied widely. Li and Weber (170) reported an off-line SPME-CE approach for the determination of barbiturates in urine and serum, utilizing a sorbent of plasticized PVC coated around a stainless steel rod. Eor extraction, the coated rod was inserted for 4 min in a Teflon tube containing 50 p.1 of sample, and next the rod was repeatedly desorbed in another Teflon tube which each time contained 5 p.1 of desorption solution. This solution was transferred to an injection vial and an aliquot was injected into the CE system (Eigure 11.19). The extraction procedure appeared to be selective and effectively allowed the handling of very small samples. 

Figure 11.19 SPME-CE analysis of urine samples (a) blank urine (a) directly injected and extracted for (b) 5 (c) 10 and (d) 30 min (b) Urine spiked with barbiturates, extracted for (e) 30 and (f, g) 5 min. Peak identification is as follows 1, pentobaitibal 2, butabarbital 3, secobarbital 4, amobarbital 5, aprobarbital 6, mephobarbital 7, butalbital 8, thiopental. Concenti ations used are 0.15-1.0 ppm (e, f) and 0.05-0.3 ppm (g). Reprinted from Analytical Chemistry, 69, S. Li and S. G. Weber, Determination of barbiturates by solid-phase microexti action and capillary electrophoresis, pp. 1217-1222, copyright 1997, with permission from the American Chemical Society.

Although on-line sample preparation cannot be regarded as being traditional multidimensional chromatography, the principles of the latter have been employed in the development of many on-line sample preparation techniques, including supercritical fluid extraction (SFE)-GC, SPME, thermal desorption and other on-line extraction methods. As with multidimensional chromatography, the principle is to obtain a portion of the required selectivity by using an additional separation device prior to the main analytical column. 

Octazatrienes or Octazones. Derivatives of HN N.NH.N N.NH.N NH, spme of which are expl. They were described by their discoverers, Wohl and Schiff (Ref 3), as standing on the very edge of existence ... 

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. 

Guidotti M, Ravaioli G, Vitali M. 1999. Total />-nitrophenol determination in urine samples of subjects exposed to parathion and methyl-parathion by SPME and GC/MS. J High Resolut Chromatogr 22(ll) 628-630. 

Solid phase micro extraction (SPME) is a techniques in which a silica fiber coated with a thin film of polymer is brought into contact with an aqueous matrix where the organics in solution partition onto the fiber. The fiber is subsequently placed into the injector of a GC where the heat causes the release of analyte onto the column. This has been applied to endosulfan (a- and (3-) and endosulfan sulfate in water with limits of detection of less than 0.3 pg/L reported (Magdic and Pawliszyn 1996). 

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