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analyses. Higher percentages of methanol were not used because the improvement was minimal, the very high proportions would resemble solvent extractions, and the advantages of using SFE would be lost. Supercritical fluid chromatography Supercritical fluid chromatographic separation of curcumin was carried out using silica, diol-silica, ODS-silica, and PS-DVB copolymer columns with methanol-modified carbon dioxide. With silica, a broad tailing peak was obtained, and curcumin was strongly retained by the diol column. Using an ODS-silica column, only one rapidly eluted sharp peak was obtained, indi cating that curcumin was not retained by the column. Reasonable separation of curcurim was achieved with the polymer column at a temperature of 60°C and 250 bar, using 25% methanol as mod ifier (Figure 4). Reducing the pressure or percentage of methanol caused increased retention. SFE-SFC of turmeric As a satisfactory SFC separation of curcuminoids could be ob tained with the PS-DBV copolymer column, on-line SFE-SFC was then studied using this column. About 10 m g of turmeric was found to be sufficient to give readily detectable peaks. In a preliminary study, it was found that a poor recovery of curcumin was obtained when this small quantity of sample was placed in the 1-mL extraction vessel. After extraction, the sample was observed to have been deposited on the wall of the vessel. Thus, the velocity and flow pattern of the extraction fluid maybe insufficient to transfer the analytes from the extraction vessel onto the column. The problem of poor extraction when using incompletely filled vessels has also been reported by Andersen and coworkers (23). To overcome this problem, an empty guard column with a much smaller volume (20 x 2 mm) was then used as an extraction cell. In order to slow the chromatographic separation in comparison to the extraction stage, and thus reduce band broadening, low per centages of methanol were used in initial experiments at 250 bar. The elution of curcumin from the PS-DVB copolymer column was very slow under these conditions. The percentage of methanol was then increased to elute the curcumin. However, as no satisfactory separations were obtained, the analyte may not have been sufficiently focused. In order to increase the extraction rate to give a small plug of Table I. Curcumin (curcumin and curcuminoids) content of turmeric as determined by SFE-SFC at 60 C followed by methanolic extraction (ME) sample, but still have reasonable retention of the column, on-line SFE-SFC was then performed using a two-stage pressure process, whereby the analyte was rapidly extracted by using a high pres sure of 250 bar and 20% methanol as modifier. The eluent was then passed through a pressure-relief valve (which controlled the extraction pressure), to the column (Figure 1), which was main tained at a lower pressure (100 bar) by the back-pressure regu lator. Therefore, the pressure, and hence the density, ofthe eluent decreased rapidly before reaching the column; this resulted in a focusing of the extract. A s the extraction proceeded, the accu mulated extract moved onto the column as a narrow plug and was then eluted. Little band broadening was observed in comparison to direct injection of a solution of the curcuminoids onto the column under the same chromatographic conditions. This method gave a distinct separation (Figure 5), in which the intense initial peak of nonpolar turmerones and sesquiterpenes were well separated from the more polar curcuminoids. Unlike re- versed-phase HPLC, in the effectively normal phase conditions of SFC, the presence of the nonpolar components did not extend the analysis time. Quantitative analysis A set of SFE-SFC extractions of turmeric was performed using various pressures and percentages of methanol as modifier in an attempt to find good extraction conditions for curcumin (Table I). In each case, to confirm that most of the curcumin has been ex tracted by SFE, the residue from the modified carbon dioxide was removed from the SFE extraction vessel and extracted with methanol. The reproducibility between two runs under the same condition was reasonable in comparison with methanol extraction, which gave a range of 5.10-5.64% curcumin over six extractions. This could be due to inhomogenity of the small sample size used or inefficient mixing of carbon dioxide and modifier. The condi tions chosen were 280 bar and 20% methanol, which gave a cur cumin content of 5.34%. This represents 95.7% of the curcumin that could be extracted with methanol. Higher percentages of methanol would significantly reduce resolution in the SFC stage. Although the percentage of curcumin was very similar by both ex traction methods, after turmeric has been subjected to SFE, methanol was capable of extracting another 0.24% curcumin. Conclusions Supercritical fluid extraction can be used as an alternative technique to solvent extraction in the extraction of curcumin from turmeric. SFE of curcumin may be accomplished by using carbon dioxide modified with methanol. The curcumin content obtained by SFE is comparable to that obtained by methanolic ex traction. On-line SFE-SFC isrelatively fast and simple, and frac tionation of the turmerones and curcuminoids is possible in a single run using a two-stage pressure process. Separation of cur cuminoids by SFC is comparable to that by HPLC. Acknowledgments The authors thank the Ministry of Science, Technology and Environment, Malaysia, for funding the research through the IRP A programme No. 2-07-07-03l;Universiti Teknologi, Malaysia for a studentship to UKA; Ciba Corning, U.K. for the loan ofthe Jasco system; and Polymer Lab for the gift of the PLRP-S column. 24 SFE conditions Curcumin content % % extracted by SFE 91.5 90.4 95.7 P(bar) %MeOH SFE 250 15 4.96 250 15 4.96 mean 4.96 250 20 4.85 250 20 5.18 mean 5.02 280 20 5.01 280 20 5.66 mean 5.34 ME Total 0.52 5.48 0.39 5.35 0.46 5.42 0.43 5.25 0.54 5.72 0.49 5.51 0.28 5.29 0.19 5.85 0.24 5.58 SFE = supercritical fluid extraction. ME = methanolic extraction after SFE. SFC conditions: 60°C, 100 bar. Quantitation was by HPLC. Journal of Chromatographic Science, Vol. 3 1 , January 1993PDF Image | Supercritical Fluid Extraction Turmeric
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