Quantitative Supercritical Fluid Chromatography

Finally, supercritical fluid chromatography, in which a supercritical fluid is used as the mobile phase, was introduced by Klesper [164-166]. SFE directly coupled to SFC provides an extremely powerful analytical tool. The efficient, fast and selective extraction capabilities of supercritical fluids allows quantitative extraction and direct transfer of the selected solutes of interest to be accomplished to the column, often without the need for further sample treatment or cleanup. Extraction selectivity is usually achieved by adjusting the pressure of the supercritical fluid at constant temperature or, less often, by changing the temperature of the supercritical fluid at constant pressure. SFE coupled with packed column SFC has found... 

Andersson P, Demirbuker M, Blomberg L. 1992. Quantitative hydrocarbon group- analysis of gasoline and diesel fuel by supercritical fluid chromatography. Journal of Chromatography 595(1-2) 301-311. 

The prerequisites for the use of gas chromatography as an analytical tool in enantiomer analysis, i.e., quantitative resolvability, substrate volatility and thermal stability, tend to restrict its general use. The development of supercritical fluid chromatography (SFC) for enantiomer... 

Heaton et al. have reported the supercritical fluid chromatography of taxicin I and taxicin II extracted by supercritical fluid extraction of Taxu baccata, the English yew tree [41]. They compared capillary- and packed- column SFC and concluded that packed-column SFC was better than capil4 lary-column SFC for quantitative analysis of these compounds. Capillary SFC was done on either a biphenyl or carbowax column with unmodified carbon dioxide as the mobile phase. The packed-column SFC was performed on a nitrile column with a mobile phase consisting of a methanol gradient with carbon dioxide. 

J.L. Janicot, M. Caude, and R. Rosset, Separation of opium alkaloids by carbon dioxide sub- and supercritical fluid chromatography with packed columns Application to the quantitative analysis of poppy straw extracts, J. Chromatogr., 437 351 (1988). 

Biermanns et al. reported the chiral resolution of /3-blockers, including propranolol, metoprolol, and atenolol using packed-column supercritical fluid chromatography [38]. A Chiracel OD column with a mobile phase of 30% methanol with 0.5% isopropylamine in carbon dioxide was used for the separation. A baseline separation of isomers was obtained in less than 5 min at a mobile-phase flow rate of 2 ml/min. While keeping the column outlet pressure constant, the flow rate was increased to 4 ml/min and it was noted that, although the retention was reduced, the resolution remained the same. Both R- and S-propranolol gave linear responses from 0.25-2500 ppm with a correlation coefficient of >0.9999. The detection limit was approximately 250 ppb for a S/N ratio of 3. The reproducibility for both R- and S-propranolol was less than 1.5%. It was also noted that 0.09% R-propranolol can be quantitated in the presence of 2500 ppm of S-Propranolol. 

P. Edder, W. Haerdi, I. Veuthey, and C. Staub, Quantitative capillary supercritical fluid chromatography and supercritical fluid extraction of basic drugs of abuse, Chimia, 46 141 (1992). 

Sato et al. (1999) developed a rapid quantitative method for estimating capsai-cinoids in placentas of Capsicum. This was achieved by employing a direct connection of supercritical fluid extraction and supercritical fluid chromatography. They suggested this method was useful as a rapid (20 min) and safe screening test for the pungency of C. annuum fruits. 

Sato, K., Sasaki, S.S., Coda, Y., Yamada, T., Nunomura, O., Ishikawa, K. and Maitani, T. (1999) Direct connection of supercritical fluid extraction and supercritical fluid chromatography as a rapid quantitative method for capsaicinoids in placentas of Capsicum. Journal Agricultural and Food Chemistry 47(11), 4665-4668. 

Indirect analysis of the enantiomeric ratio of an alcohol can be accomplished via separation and quantitation of the diastereomers of eq 1 by high-performance liquid chromatography (HPLC), gas-liquid chromatography (GLC), or supercritical fluid chromatography (SFC). For example, diastereomeric diacylglycerol l-(l-naphthyl)ethyl carbamates are separated by HPLC on a silica gel column, as are the diastereomeric derivatives of the tertiary monoterpene alcohol linalool, diastereomers of (unsym-... 

Ryan, T.W. Yocklovich, S.G. Watkins, J.C. Levy, E.J. Quantitative analysis of additives in polymers using coupled supercritical fluid extraction-supercritical fluid chromatography. J. Chromatogr. 1990, 505, 273 - 282. 

The choice of the most suitable instrumental technique depends on several factors, such as the physical-chemical characteristics of analytes, the detection limits required, the level and type of interferences, the resolution needed, the identification power required, the accuracy and the precision of the quantitative determination, the availability of instrumentation and finally the cost and the time necessary per each determination. Moreover, extraction and clean-up procedures have to be suitably matched with instrumental analysis. GC coupled with Electron Capture Detection (ECD) or Mass Spectrometry (MS) has been widely applied for the determination of PCBs in organic extracts of environmental samples. In few cases the instrumentation includes the extraction step, such as an SEE system coupled with Supercritical Fluid Chromatography (SFC) or with GC (40). 

Characterization in the solid-state and compendial methods has been discussed already. Quantitative tests to characterize drug substance and drug product composition require that significant consideration be given to method development. Methods such as thin layer chromatography, gas chromatography, HPLC, supercritical fluid chromatography, and capillary electrophoresis... 

Hedrick J, Taylor LT. Quantitative supercritical fluid extraction—supercritical fluid chromatography of a phosphonate from aqueous media. Anal Chem 1989 61 1986-1988. 

Li JJ. Quantitative analysis of cosmetic waxes by using supercritical-fluid extraction(SFE)/supercritical-fluid chromatography (SFC) and multivariate data analysis. Chemom Intell Lab Syst 1999 45 385-395. 

Separation of kavalactones was also achieved by supercritical fluid chromatography using methanol-modified carbon dioxide as the mobile phase. An optimal separation was achieved on either an amino or protein C4 column at 125 atm and 80 °C. Semipreparative separation of kavalactones was also obtained with two columns connected in series (Ashraf-Khorassani etal., 1999). A micellar electrokinetic chromatographic method with diode-array detection has also been developed for the identification and quantitative determination of the major kavalactones from extracts of P. methysticum... 

C. Poole, The Essence of Chromatography, Elsevier, Amsterdam, 2003. (A 927-page book that provides a comprehensive survey of the current practice of chromatography. It includes an in-depth and well-referenced treatment of chromatographic theory and quantitative principles. It covers HPLC, GC, thin-layer chromatography, supercritical fluid chromatography, and capillary electrophoresis (CE).)... 

Supercritical fluid chromatography can be used as a qualitative or quantitative technique. Qualitative information allows a substance to be identified on the basis of retention time comparisons between a standard and the sample. When used quantitatively, the SFC can employ external or internal standards to generate a standard curve. Then, the peak area of the sample peak on the chromatogram can be used to obtain a concentration. An example of an SFC instrument is shown in Figure 3.35. 

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