Preparative supercritical fluid chromatograph

Fig. 16.5. Preparative supercritical fluid chromatographic system, customized for high throughput organic synthesis (HTOS) screening [11],...

Collection of Fractions from the Preparative Supercritical Fluid Chromatograph... 

Jusforgues P, Shaimi M, Barth D. Preparative supercritical fluid chromatography grams, kilograms, tons. In Anton K, Berger C, eds. Supercritical Fluid Chromatography with Packed Columns. Chromatographic Science Series. Vol. 75. New York Marcel Dekker, 1998, Chap 14. 

Neither MAE nor ASE is currently in a configuration that would readily lead to the automation of sample preparation. Supercritical fluid extraction can be used as online system that can then be connected to the chromatographic and detection systems. Connected online with the GC/MS, SFE was successfully used for the determination of PAHs in marine sediments. Using either CO2 alone or modified with toluene or MeOH in the extraction, the PAHs were cryofocused in the accumulation cell of the GC and then directly chromatographed. For the study of PAHs in marine sediments, a new extraction technique, which consists of the combination of ASE (dynamic and static mode) and SFE (dynamic mode), was developed, with an extraction time longer than in ASE but shorter than in SFE, and... 

The improvement of compound quality through chromatographic purification has had great influence on compound collections since the change of the century [50]. Large purification platforms based on mass-triggered preparative HPLC have been set up [51]. The latest development is the use of preparative supercritical fluid chromatography (SFC) [52]. 

The collection of eluent fractions from a conventional preparative HPLC is a trivial matter. Provision of automated fraction collectors suitable for HPLC is no commonplace and instrumentation is highly developed and widely commercially available. However, collection of eluent from a preparative SFC is not trivial, particularly if complete collection of a fairly volatile solute is required. In a supercritical fluid chromatograph using carbon dioxide the expansion of the fluid at depressurisation is very large indeed. If carbon dioxide is depressurised from 300 Bar (4500 psi) to atmospheric pressure is expands to 355 times its original volume if its temperature is maintained constant. Hence at a flow rate of lOcm min" of supercritical carbon dioxide at 300 Bar, which corresponds to about 7 g carbon dioxide per minute, expansion after depressurisation yields 3.5 L of carbon dioxide gas per minute at NTP. 

Recent developments in the preparative supercritical fluid chromatography and extraction area include the following commercially available instruments and iimova-tions. Suprex have introduced the Prepmaster and Accutrap, two new products for automated quantitative sample preparation. The Prepmaster is a dedicated supercritical fluid ctraction system designed for analytical and semi-preparative extractions. It can be used on-line, directly interfaced to a gas chromatograph or SFC or off-line with the Accutrap cryogenic collection module. The Prepmaster can accommodate extraction vessels with capacities from 0.5 to 8 mL. 

S. A. Westwood (Ed.), Supercritical Fluid Extraction and its Use in Chromatographic Sample Preparation, CRC Press, Boca Raton, PE (1992). 

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

The coupling of supercritical fluid extraction (SEE) with gas chromatography (SEE-GC) provides an excellent example of the application of multidimensional chromatography principles to a sample preparation method. In SEE, the analytical matrix is packed into an extraction vessel and a supercritical fluid, usually carbon dioxide, is passed through it. The analyte matrix may be viewed as the stationary phase, while the supercritical fluid can be viewed as the mobile phase. In order to obtain an effective extraction, the solubility of the analyte in the supercritical fluid mobile phase must be considered, along with its affinity to the matrix stationary phase. The effluent from the extraction is then collected and transferred to a gas chromatograph. In his comprehensive text, Taylor provides an excellent description of the principles and applications of SEE (44), while Pawliszyn presents a description of the supercritical fluid as the mobile phase in his development of a kinetic model for the extraction process (45). 

Current interest in supercritical fluid extraction as a sample preparation technique for chromatographic analysis is intense, in spite of it receiving very little tion until the mid-1980s. Although neglected by analytical cl Hsts, during the... 

A.L. Howard and L.T. Taylor, in Supercritical Fluid Extraction and Its Use in Chromatographic Sample Preparation (S.A. Westwood, ed.), Blackie, London... 

Klesper, E. Corwin, A. H. Turner, D. A. J. Org. Chem., 1962, 27, 700. Sugiyama, K. Saito, M. Hondo, T. Seda, M. J. Chromatogr. 1985, 332, 107. Anderson, I. G. M. Supercritical fluid extraction coupled to packed column supercritical fluid chromatography. In Supercritical Fluid Extraction and Its Use in Chromatographic Sample Preparation Westwood, S. A. Ed., Blackie Academic and Professional, Chapman and Hall UK, 1993 p. 112. 

Packed-column SFC also is suitable for preparative-scale enatioseparations. Compared with preparative LC, sub- or supercritical fluid chromatography results in easier product and solvent recovery, reduced solvent waste and cost, and higher output per unit time. Because of its reduced sample capacity, SFC usually allows the separation of 10-100 mg samples per run. Chromatographers can compensate for these sample amounts by using shorter analysis times and repetitive injections (Wolf and Pirkle, 1997). 

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