SPE-SFE-GC

Supercritical fluid extraction (SFE) and Solid Phase Extraction (SPE) are excellent alternatives to traditional extraction methods, with both being used independently for clean-up and/or analyte concentration prior to chromatographic analysis. While SFE has been demonstrated to be an excellent method for extracting organic compounds from solid matrices such as soil and food (36, 37), SPE has been mainly used for diluted liquid samples such as water, biological fluids and samples obtained after-liquid-liquid extraction on solid matrices (38, 39). The coupling of these two techniques (SPE-SFE) turns out to be an interesting method for the quantitative transfer 

The System is built by using three independent modules (SPE, SEE and GC) in Such a way that it can be assembled to perform experiments in the on-line coupled mode (SPE-SEE, SEE-GC, SPE-GC and SPE-SEE-GC) or as independent units (GC, SPE, and SEE). This means that if we want to use the system for standard GC, there will be no problems, with the same applying for both SPE and SEE. 

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Figure 6.4 Schematic diagram of an on-line SPE-SFE-GC system (from ref. 40) 1, carbon dioxide 2, high-pressure syringe pump 3, gas cliromatograph 4, tliree-poit valve 5, oven 6, extraction cell 7, waste 8, ten-port valve 9-11 conditioning and washing solvents 12, sample 13, niti Ogen.

Figure 15.14 Separation of explosives exnacted from water by using SPE-SFE-GC at several SEE trapping temperatures, peak identification is as follows NG, nitroglycerin 2,6-DNT, 2,6-dinitrotoluene 2,4-DNT, 2,4-dinitrotoluene TNT, triniti otoluene IS, 1,3-tiichloroben-zene. Adapted Journal of High Resolution Chromatography, 16, G. C. Slack et al., Coupled solid phase extraction supercritical fluid extraction-on-line gas cliromatography of explosives from water , pp. 473-478, 1993, with permission from Wiley-VCH.

Hyphenation On-line GC, HPLC, SPE-SFE, SFE-SPE GC (most common), HPLC. Direct thermal desorption. 

In addition to standard liquid injection there are many GC accessories which can provide different methods of sample introduction to the column, such as HS, SPE, SFE, TD, TG, Py, etc. Examples of such GC-FTIR devices are TD-GC-FT1R (with a cryostat interface) and PyGC-FTIR. 

SFE-GC-MS is particularly useful for (semi)volatile analysis of thermo-labile compounds, which degrade at the higher temperatures used for HS-GC-MS. Vreuls et al. [303] have reported in-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of organics in water samples. Automated in-vial LLE-GC-MS requires no sample preparation steps such as filtration or solvent evaporation. On-line SPE-GC-MS has been reported [304], Smart et al. [305] used thermal extraction-gas chromatography-ion trap mass spectrometry (TE-GC-MS) for direct analysis of TLC spots. Scraped-off material was gradually heated, and the analytes were thermally extracted. This thermal desorption method is milder than laser desorption, and allows analysis without extensive decomposition. 

A method for the detection of 3-blockers in urine by SPE-SFE was developed, using acetic anhydride and pyridine as acetylation reagents in the SFE vessel (130). The detection was carried out by GC-MS. The same method was later applied to the detection of the same analytes in serum and urine (131). Unmodified CO2 at 40°C and 272 bar has been used for the multiresidue SFE of methyltestosterone, nortestosterone, and testosterone at low... 

SPE is an alternative rapid sample preparation mode for GC and HPLC (cf. Sections 7.1.1.2 and 7.1.1.6). Combination of SPE and SFE provides a solvent-less preparation technique. In this approach, the sample can... 

There are basically three methods of liquid sampling in GC direct sampling, solid-phase extraction and liquid extraction. The traditional method of treating liquid samples prior to GC injection is liquid-liquid extraction (LLE), but several alternative methods, which reduce or eliminate the use of solvents, are preferred nowadays, such as static and dynamic headspace (DHS) for volatile compounds and supercritical fluid extraction (SFE) and solid-phase extraction (SPE) for semivolatiles. The method chosen depends on concentration and nature of the substances of interest that are present in the liquid. Direct sampling is used when the substances to be assayed are major components of the liquid. The other two extraction procedures are used when the pertinent solutes are present in very low concentration. Modem automated on-line SPE-GC-MS is configured either for at-column conditions or rapid large-volume injection (RLVI). 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

Applications The potential of a variety of direct solid sampling methods for in-polymer additive analysis by GC has been reviewed and critically evaluated, in particular, static and dynamic headspace, solid-phase microextraction and thermal desorption [33]. It has been reported that many more products were identified after SPME-GC-MS than after DHS-GC-MS [35], Off-line use of an amino SPE cartridge for sample cleanup and enrichment, followed by TLC, has allowed detection of 11 synthetic colours in beverage products at sub-ppm level [36], SFE-TLC was also used for the analysis of a vitamin oil mixture [16]. 

Temazepam and morphine have been separated from a whole blood matrix using SC CO2. In the first instance, the extractants were CO2 and ethyl acetate at 65°C and 207 bar, and recoveries ranged from 80% to 100%. The extraction was monitored at 254 nm, with individual separation of the analytes carried out by high-performance liquid chromatography (HPLC). For morphine extraction from dried blood, methanol/triethylamine was added as a modifier to 90% CO2 at 100°C and 241 bar, and the extracts were analyzed by GC-MS. The SFE method proved to be faster and cleaner than solid-phase extraction (SPE). 

A combination of SFE and SPE as a sample preparation technique for the ultratrace analysis of mebeverine alcohol in plasma has been proposed (123). Plasma containing the analyte was applied to conditioned octadecylsi-lane cartridges. After washing and drying, the packing was placed in an SFE system. Carbon dioxide with 5% methanol was used as the SCF at 40°C and 355 bar. The extract analysis was carried out by GC-MS. A similar method was used for the extraction of flavone, also from blood plasma, but the determination was performed by HPLC in this case (124). In other applications, plasma spiked with tritiated budesonide to 93 nM was deposited onto a filter paper placed in the extraction vessel, where the extraction was performed with pure CO2 for 30 min then, the budesonide in the extract was determined with a liquid scintillation counter. The recoveries were over 80% (125). " C-Fla-vone and C-ketorolac were extracted from plasma at various extraction pressures and times to test recovery (126). The SCF was CO2 at 60°C and 300 bar. The recoveries were determined by liquid scintillation counting and ranged from 85% to 98% for C-flavone (RSD = 3.8-5.8%, three replicates). 

Samples containing nonvolatile materials present problems for gas chromatography. The non-volatiles cannot be injected into the GC as they will rapidly plug up the injection port and may destroy the GC column. Common sample preparation steps for isolating the volatiles from the nonvolatile sample matrix include liquid-liquid extraction, solid phase extraction (SPE), solid phase microextraction (SPME), supercritical fluid extraction (SFE), and headspace. SPE and SPME for GC are discussed in a recent review article by Penton [15]. 

Supercritical fluid extraction (SFE) has been used mostly in environmental analysis [129,205] for the extraction of nonpolar organic pollutants from solid samples, for example, sediments. The technique has abo been used together with SPE dbks (silica Cis, polymeric, and ion exchanger disks) for the extraction of phenols from water samples followed by GC-MS [206]. After adsorbing the phenols onto the SPE disk, they are eluted with a supercritical fluid (carbon dioxide). 

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