Applications of SPME

SPME can also be used to extract target analytes from food and drug samples. Thus, it has been employed for the extraction of caffeine from coffee and tea [225], and for that of volatile impurities in drugs. Headspace SPME has also been tested for flavour analysis in foods. Thus, the SPME/GC/TOF-MS tandem was successfully used for the rapid analysis of volatile flavour compounds in apple fruit. The sample (300-450 g of apple) was subjected to static headspace sampling for 4 6 h in order to allow the volatiles 

Solid sample treatments involving the removal of volatile species 

COMPARISON OF IMMERSION AND HEADSPACE SPME ANALYSIS OF PETROCHEMICAL WASTEWATER 

The characterization of water-soluble components in slurries is one use of SPME with mixed solid-liquid samples. In one application, dried homogenized solid samples (10 mg of sewage sludge or sediment) were slurried in 4 ml of H,0 saturated with NaCl and adjusted to pH 2 with HCl for extraction for 1-15 h, which was followed by desorption into 4 1 methanol/ethanol over 2 min. The extracted compounds were either injected into a liquid chromatograph or fed directly via an electrospray ionization interface to a mass spectrometer with 1 s miz scans from 50-700 or selected-ion monitoring. The major components extracted included phthalates, fatty acids, non-ionic surfactants, chlorinated phenols and carbohydrate derivatives [235]. 

Nakahara, Hydride Generation, in Sample Introduction in Atomic Spectroscopy, J. Sneddon Ed., Elsevier, Amsterdam (1990). 

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Macpherson T, CW Greer, E Zhou, AM Jones, G Wisse, PCK Lau, B Sankey, MJ Grossman, J Hawari (1998) Application of SPME/GC-MS to characterize metabolitres in the biodesulfurization of organosulur model compounds in bitumen. Environ Sci Technol 32 421 26. 

For further applications the reader is referred to Pawliszyn [549]. Application of SPME in water analysis has been reviewed [536]. 

MacPherson, T. Greer, C.W. Zhou, E., et al., Application of SPME/GC-MS to Characterize Metabolites in the Biodesulfurization of Organosulfur Model Compounds in Bitumen. Environmental Science Technology, 1998. 32(3) pp. 421—426. 

Kopinke, F.-D., J. Porschmann, and A. Georgi, Application of SPME to study sorption phenomena on dissolved humic organic matter . In Applications of Solid Phase Microextraction, J. Pawliszyn, Ed., Royal Society of Chemistry, Cambridge. UK, 1999, pp. 111-128. 

Gas chromatography/olfactometry (GC/O) based on dilution analysis (e.g., CharmAna-lysis or Aroma Extraction Dilution Analysis) gives an indication of what compounds are most potent in the aroma of foods. The application of SPME to GC/O dilution analysis can be achieved by varying the thickness of the fiber phase and the length of exposure, resulting in various absorbant volumes. 

The technique is very simple, fast, and does not employ any organic solvents either for sample preparation or clean-up. This makes it highly desirable because, unlike other methods, it does not release environment-polluting organic solvents into atmosphere. Thus far, the technique has been successfully applied to the determination of a wide variety of organic compounds. However, the application of SPME to determine the nitrosamines could eliminate some problems like the widespread solvent use and the lengthy and time-consuming sample preparation steps (that are common in most of the published methods in this area). 

Boyd-Boland and Pawliszn reported the first application of SPME to the analysis of herbicide residues in 1995, for the simultaneous determination of nitrogen-containing herbicides in soU, water, and wine samples.Herbicides have been extracted following the three extraction modes (DI, HS, and in-tube), but direct insertion mode was the most used for these compounds. Krutz et al. have recently published an exhaustive review dealing with SPME for herbicide determination in environmental samples. 

Some relevant applications of SPME, SFE, PFE, and MAE for the extraction of herbicides in solids are presented in Table 26.5. 

One of the first applications of SPME to phthalate analysis was the development of a method for the extraction of DEP from water. The final analysis was done by LC-UV. Different parameters were optimized including four types of fibers. Carbowax-template resin (CW-TRP) and polydimethylsiloxane-divinylbenzene (PDMS-DVB) were found suitable to perform phthalate extraction. The other two fibers, polyacrylate (PA) and polydimethylsiloxane (PDMS), were discarded due to low response and broad peaks, respectively. Samples were extracted at room temperature by direct exposition of the fiber to the sample, previously enriched with 25% of NaCl. The linearity achieved was good from 5 to 50 /rg/1. Higher concentrations show a lost of linearity that could suggest the saturation of the fiber coating. Detection limit was 1 ng/ml. 

Solid Phase Micro-extraction Solid phase micro-extraction (SPME) was developed in 1989 by Pawliszyn and coworkers °" ° as a simple and effective adsorption/adsorption and desorption technique that eliminates the need for solvents. Applications of SPME in the analysis of drugs have been reviewed, as well as the possibilities of interfacing SPME with HPLC. ° SPME... 

Jimenez, A., Beltran, G., and Aguilera, M.P., Application of SPME to the analysis of volatile compounds in virgin olive oils, J. Agric. Food Chem., 46, 2744,1998. 

Applications of SPME for preconcentration of drugs like amphetamines from urine coupled with electrospray ionization (ESI) IMS or of metabolites and ephedrine" from nrine and of methamphetamines from human serum were also demonstrated. These are discussed in Section 14.4. 

As indicated above the fiber coatings can range from a rather nonpolar polydimethyl-siloxane to the more polar polyacrylate film. The polydimethylsiloxane phase is used for the determination of nonpolar volatile compounds in water samples [174,175]. In comparison, the polyacrylate fiber is preferred for the extraction of more polar compoimds. The first application of SPME to the analysis of polar compounds was the determination of phenols performed by Buchholz and Pawlisz)m [176]. These authors reported a detection limit at the ng/L level for the GC/FID and GC/MS procedures using a saturated sodium chloride solution at pH 4 to increase the SPME sensitivity. In connection with... 

Since its inception in 1990, there have been nearly 1000 papers published in the literature employing SPME. Headspace SPME alone cam account for must of the increase in publications on headspace-related techniques since 1997. Among these papers, there are myriad applications. Supelco has produced an applications guide that lists about 500 of these (74). In general, applications of SPME are seen in environmental analysis, including air, soil, and water, food, natural products, pharmaceuticals, and clinical and forensic analysis, plus numerous articles on theoretical aspects. SPME has proved to be one of the most versatile sample preparation techniques available. 

Pawliszyn and the author first reported on the technique of solid-phase microextraction (SPME) in 1990 (48). Since that time SPME has been commercialized (Supelco, Bellefonte, PA) and the number of applications of SPME to environmental analysis has exploded (7,49,50). When used for gas chromatography the technique requires no solvent. Solid-phase microextraction can be used to extract analytes from an aqueous phase or the gas phase. The technique can be used to sample the headspace over water and soil samples. 

TABLE 15.11 Applications of SPME to VOCs in Environmental Analysis... 

Also in solid-phase microextraction (SPME) analytes are typically not extfacted quantitatively from the matrix. However, when partition equilibrium is reached, the extracted amount of an analyte is proportional to its initial concentration in the sample matrix phase. As indicated by Ai [33], application of SPME for quantitative analysis is feasible also when the partition equilibrium is not attained. Pawliszyn [34] has reviewed the quantitative aspects of SPME. Provided proper calibration strategies are followed, SPME can yield quantitative data and excellent precision, reproducibility and linearity (detection limits of 15 ng/L). In terms of precision, linearity and sensitivity SPME equals HS techniques. 

Similar to those of sampling headspace with gastight syringes, the results obtained by SPME were highly dependent on absorption conditions as well as type of fiber used. Because of the large variety of fibers available (e.g., PDMS, DVB, Carboxen, including fiber combinations) as well as the development of new and improved techniques [e.g., headspace sorptive extraction (HSSE) [8]], a detailed description would be too extensive for this chapter. However, an excellent review [12] as well as theoretical aspects [4] and applications of SPME in food, flavor, and fragrance have been published [5-7]. 

There is a rapidly expanding literature on the application of SPME for the analysis of essential oils and plant systems, and the utility of SPME for monitor-... 

This section describes the equipment used for the analysis by SPME. The mechanical application of SPME is analogous to liquid injection by hand. The startup costs are small and a vast amount of information can be gained rather quickly. Typically, for a laboratory already performing GC analysis, all that is needed are SPME fibers and an SPME holder. A pack of fibers and a holder can be obtained for several hundred dollars. No modifications to a GC are needed. It is recommended that a reduced inlet liner (0.7 mm I.D.) be used in the injection port, although SPME can be successfully performed with a standard inlet liner. The injection of 1 ql of liquid sample will rapidly expand to till the 1 ml volume of a typical inlet liner. Because there is no liquid solvent being injected with SPME, there is no need for the relatively large inlet volume. The reduced volumes in the injection port produce narrow injection bandwidths resulting in sharper GC peaks. 

This chapter describes the application of SPME to develop a rapid, sensitive analytical technique for analyzing the volatile compounds found in the headspace of rice. A key requirement of this methodology is the heating of the sample in order to produce sufficient amounts of analytes to be successfully analyzed. Analysis of less than 1-g samples of milled or brown rice kernels is possible. The key odorant in fragrant rice is 2-AP, and recoveries are enhanced by the addition of water. However, the recovery of other compounds may be suppressed by the addition of water, as observed with the internal standard TMP. This method is readily amenable for the analysis of additional compounds once they have been identified as having an impact on the sensory quality of rice. 

Many products advertise long-lasting fresh clean odors on fabric or in your home. These claims are often subjective panel judgments but they can be supported by analytical measurements from the respective substrates. Two applications of SPME have involved developing sampling methods to measure substantivity from cloth and tile. 

The main application of SPME as clean-up procedure for PAHs monitored in air has been its headspace (HS) mode combined with microwaves for the analysis of XAD-2 resins [87]. Three different SPME fibers were used in the study 65 pm PDMS-DVB, 85 pm PA, and 100 pm PDMS. The microwave power was 120 W during 40 min, while the HS-SPME mode was simultaneously carried out. 

In addition to the the solid-phase microextraction (SPME) applications in clean-up steps or in passive sampling, it has also been proposed the use of SPME in extraction schemes for PAHs, mainly contained in drinking waters. Table 19 summarizes several applications of SPME in water samples, as well as the optimum extraction conditions to reach successful limits of detection. The applications are always carried out in direct immersion mode. 

Table 19. Reported applications of SPME in the extraction step of PAHs from water samples... 

In summary, SPME-DED satisfactorily extracts low MW PAHs from smoked foodstuffs but it seems that the application of SPME-DED on solid matrixes and foodstuffs is limited by the volatility of the targeted compounds. However, this circumstance does not invalidate the potential application of SPME-DED on PAHs analysis from solid matrixes, since SPME-DED would be a useful screening method for those studies in which the aim is the evaluation... 

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