Direct coupling of capillary supercritical fluid chromatography with supercritical fluid extraction using modified carbon dioxide

Capillary supercritical fluid chromatography has been directly coupled with supercritical fluid extraction using modified carbon dioxide. The mixed fluids were prepared with a single pump on-line mixing system. The most important step in the SFE-SFC interface was the elimination of the modifier solvent. This was achieved by use of a coupled trap, 0.1 mm i.d. and 0.53 mm i.d. capillary tubing connected in series, with the collected solutes refocused on the second (0.53 mm i.d.) trap before transfer into the separation column. This enabled complete elimination of various modifier solvents and high efficiency collection of the solutes. The effect of the modifier on trapping efficiency was investigated using methanol, ethanol, dichloromethane, hexane, and toluene at a variety of concentrations. n-Eicosane was, for example, trapped quantitatively by modified carbon dioxide containing up to 13 % (w/w) methanol. The use of the technique has been demonstrated by selective extraction of n-paraffins, fatty acid methyl esters, and alcohols from a silica matrix; the effect of different modifiers on the extraction of a mixture of pesticides from soil has also been investigated.     

Oil-in-water analysis using supercritical fluid extraction interfaced with fixed wavelength infrared detection

The combination of a direct aqueous supercritical fluid extraction system interfaced to a fixed wavelength infrared detector; measuring CH₂ (ν_asymmetric) absorbance at 2930 cm^?1, has been successfully developed for the analysis of oil-in-water. Using an optional, in-line silica gel treatment procedure, method accuracy for determining Brent Delta crude oil in spiked 500 mL water samples was 92.0% to 94.5% with RSD 4.7% to 6.5%. The supercritical fluid extraction-infrared method enables a second analysis of the same water sample without silica gel treatment. For second sets of analyses without silica gel treatment, method accuracy for determining Brent Delta crude oil in spiked 500 mL water samples was 87% to 96.0% with RSD 7.5% to 9.5%. Results of this study indicate that the silica gel treatment procedure reduces the calculated level of Brent Delta crude oil-in-water by 6.6–12.4% relative to samples analysed without silica gel treatment. The results of a study involving Fourier transform infrared spectroscopy indicate a limit of detection for n-decane of approximately 0.5 mg L^?1 by measuring CH₂ (ν_asymmetric) absorbance using the supercritical fluid extraction-infrared method. Sample preparation using direct aqueous supercritical fluid carbon dioxide extraction provides an indefinite means for the use of infrared techniques to measure oil-in-water.     

Analysis of sulphonamides using supercritical fluid chromatography and supercritical fluid chromatography-mass spectrometry

Packed-column supercritical fluid chromatography has been used for the separation of mixtures of sulphonamides on silica and amino-bonded stationary phases utilizing carbon dioxide with methanol modifier as the mobile phase. The effect of modifier concentration, column pressure and modifier identity on retention was also studied. Packed-column supercritical fluid chromatography-mass spectrometry (SFC-MS) of these mixtures utilizing both moving-belt and modified thermospray interfaces was also studied. The identification of sulphamethazine in a spiked porcine kidney extract was performed by SFC-MS using the moving-belt interface.     

Optimization of supercritical fluid extraction of volatile constituents from a model plant matrix

-Cellulose has been used as a model plant matrix to investigate the conditions required to optimize the supercritical fluid extraction of typical plant constituents, limonene, caryophyllene, carvone, eugenol and santonin, using carbon dioxide as the extraction medium. The conditions required for the successful recovery of the analytes were monitored by gas-liquid chromatography. Timed recovery studies enabled differences in the rates of extraction to be determined to ensure that sufficiently long extraction runs were used. Subcritical and supercritical extractions over the ranges −10 to 80°C and 50–250 bar were examined and 250 bar and 40°C were chosen as the optimum conditions. The effects of the addition of modifiers to the supercritical fluid were also examined. The work also demonstrated that increased selectivity for polar analytes such as lactones could be obtained by trapping the extract on a silica column coupled with selective elution.     

Direct sample injection in supercritical fluid chromatography with packed fused silica column

A direct sample injection technique was developed for supercritical fluid chromatography in a packed capillary column, with carbon dioxide as mobile phase and a flame ionization detector. The method allowed solutions, neat liquids, and even solids to be introduced as samples. Also, extraction with supercritical carbon dioxide was combined with this method to separate polymer additives.     

Applications of supercritical fluid extraction (SFE) of palm oil and oil from natural sources

Supercritical fluid extraction (SFE), which has received much interest in its use and further development for industrial applications, is a method that offers some advantages over conventional methods, especially for the palm oil industry. SC-CO? refers to supercritical fluid extraction (SFE) that uses carbon dioxide (CO?) as a solvent which is a nontoxic, inexpensive, nonflammable, and nonpolluting supercritical fluid solvent for the extraction of natural products. Almost 100% oil can be extracted and it is regarded as safe, with organic solvent-free extracts having superior organoleptic profiles. The palm oil industry is one of the major industries in Malaysia that provides a major contribution to the national income. Malaysia is the second largest palm oil and palm kernel oil producer in the World. This paper reviews advances in applications of supercritical carbon dioxide (SC-CO?) extraction of oils from natural sources, in particular palm oil, minor constituents in palm oil, producing fractionated, refined, bleached, and deodorized palm oil, palm kernel oil and purified fatty acid fractions commendable for downstream uses as in toiletries and confectionaries.     

Peak compression in semi-preparative supercritical fluid chromatography

Summary Peak compression of a dihydropyridine drug, clevidipine, is obtained in both analytical and semi-preparative scale supercritical fluid chromatography, resulting in extremely high apparent efficiencies. The observed effect, when utilising a carbon dioxide/2-propanol mobile phase with a bare silica stationary phase, is achieved when the retention of the clevidipine peak is controlled to coalesce with a system peak, generated as a result of having water in the sample. Apparent efficiencies of 350,000 and 170,000 plates meter⁻¹ were obtained when 0.25 and 0.5 mg, respectively, are directly injected to a 200×4.6 mm ID 5 μm Hypersil silica packed column. The effect was extended to a semi-preparative system where apparent efficiencies in the region of 2,000,000 plates meter⁻¹ were observed when 0.3 mg of a clevidipine sample containing 80% water was injected to a 250×10 mm I.D. column containing 5-μm Hypersil silica particles.     

Analysis of conjugated bile acids by packed-column supercritical fluid chromatography.

A rapid method has been developed for the simultaneous separation of the polar glycine- and taurine-conjugated bile acids by packed-column supercritical fluid chromatography. Samples were analysed on a cyanopropyl-bonded silica column with ultraviolet detection at 210 nm and carbon dioxide modified with methanol as the mobile phase. The influence of the stationary phase, modifier concentration, temperature, column pressure and modifier identity on retention was also studied. This new chromatographic method is applicable to the assay of conjugated bile acids in duodenal bile samples from patients with hepatobiliary diseases.     

Extraction and isolation of diphenylheptanes and flavonoids from Alpinia officinarum Hance using supercritical fluid extraction followed by supercritical fluid chromatography

In this paper, an off-line combination method of supercritical fluid extraction and supercritical fluid chromatography was developed for the selective extraction and isolation of diphenylheptanes and flavonoids from Alpinia officinarum Hance. The enrichment of target components was successfully achieved using supercritical fluid extraction with the following conditions (8% ethanol as co-solvent at 45°C and 30 MPa for 30 min). Taking full advantage of the complementarity of supercritical fluid chromatography stationary phases, a two-step preparative supercritical fluid chromatography strategy was constructed. The extract was firstly divided into seven fractions on a Diol column (250 × 20 mm internal diameter, 10 μm) within 8 min by gradient elution increasing from 5% to 20% modifier (methanol) at 55 ml/min and 15 MPa. Then the seven fractions were separated by using a 1-AA or a DEA column (250 × 19 mm internal diameter, 5 μm) at 50 ml/min and 13.5 MPa. This two-step strategy showed superior separation ability for structural analogs. As a result, seven compounds, including four diphenylheptanes and three flavonoids with high purity, were successfully obtained. The developed method is also helpful for the extraction and isolation of other structural analogs of traditional Chinese medicines.     

Simultaneous analysis of antioxidants and preservatives in cosmetics by supercritical fluid extraction combined with liquid chromatography-mass spectrometry

This study evaluated supercritical fluid extraction (SFE) combined with liquid chromatography-mass spectrometry (LC-MS) to determine trace preservatives and antioxidants including methylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alpha-tocopherol (alpha-t) and alpha-tocopherol acetate (alpha-ta) in cosmetic products. A supercritical fluid extraction procedure was used to isolate four paraben preservatives and four antioxidants from the cosmetic matrix before quantitative analysis. The optimum extraction condition was performed with static extraction for 5 min, then dynamic extraction for 20 min by using carbon dioxide supercritical fluid at 14,000 kPa and 65 degrees C. Methanol was used as collection solvent and the sea sand was chosen as a filling material. The analytes were separated on a C18 reversed-phase column using methanol-water as mobile phase and quantified by measuring its mass spectrometry. The linearity range is from 10 to 20,000 ng/g with RSD values below 18%. Detection limits are achieved at the level of 4.7-142 ng/g. It was successfully applied to the determination of paraben preservatives and antioxidants in cosmetics without tedious pretreatment.     

Screening and confirmation of PAHs in vegetable oil samples by use of supercritical fluid extraction in conjunction with liquid chromatography and fluorimetric detection

A fast, simple, non-destructive method for the direct screening of polycyclic aromatic hydrocarbons (PAHs) in vegetable oil samples is proposed. The method uses a supercritical fluid extraction (SFE) system coupled on-line with a fluorimetric detector to determine PAHs. This special assembly avoids the main problems encountered in the determination of PAHs in complex matrices such as vegetable oils. PAHs are selectively extracted by using silica gel in the thimble and cleaned up by passage through a C18 column. Interferences are preferentially retained by the silica gel during the SFE process while PAHs are adsorbed in the C18 column and the remainder of the matrix is sent to waste. Finally, the C18 column is purged to remove residual CO₂ gas and adsorbed PAHs are recovered by desorption with a solvent. The extracts from positive samples are subsequently analyzed by liquid chromatography (LC) with fluorescence detection. The proposed method allows the confirmation of vegetable oil safety and hence provides a new tool for consumer protection.     

The use of nitrous oxide for supercritical fluid extraction of pharmaceutical compounds from animal feed

Supercritical fluid extraction (SFE) coupled “off-line” with HPLC analysis has been applied to pharmaceutical analysis: two different matrixes (rodent and dog feed) were spiked with compounds under investigation in pharmacological studies in order to study the supercritical extraction of such matrixes prior to further analysis and quantification of the compounds of interest. The fluid flow-rate in the SFE system was governed by the geometric characteristics (internal diameter and length) of the linear fused silica capillaries. The changes in fluid flow-rate, between experiments, for each new restrictor, required the introduction of the term Total Gaseous Fluid Volume (TGFV), which enabled a series of extraction results to be compared. The comparative behavior of nitrous oxide and carbon dioxide as supercritical extraction fluids was investigated. Results obtained using pure supercritical fluids with high solvating power (density 0.79 g ml^?1) and fluids modified with a polar liquid solvent (methanol and acetonitrile) are discussed.     

Fast supercritical fluid chromatography of polymers using packed capillary columns

Summary Fast separations of perfluorinated polyethers and polymethylsiloxanes that are composed of 50–80 oligomers were demonstrated in packed capillary column supercritical fluid chromatography (SFC) using a carbon dioxide mobile phase. Separations were accomplished within 10 min using a 13 cm×250 μm i.d. column packed with 2 μm porous octadecyl bonded silica (ODS) particles. Effects of particle diameter of the packing material and pressure programming on separation were investigated, and packed column SFC was compared with open tubular column SFC. Results show that as the particle diameter was decreased from 5 to 3 to 2 μm and the column length was reduced from 85 to 43 to 13 cm, the separation time could be reduced from 70 to 20 to 10 min while still maintaining similar separation (resolution). Short columns packed with small porous particles are very suitable for fast SFC separations of polymers.     

Pesticide multiresidue analysis of 303 compounds using supercritical fluid extraction.

Compared to generally used solvent extraction methods, supercritical fluid extraction (SFE) with carbon dioxide has the advantages of automation and simple operation in preparing samples for pesticide residue analysis. This report is the outcome of our evaluation of the practicality of SFE for the preparation of samples for pesticide residue analysis. We studied the recovery of 303 compounds with several crops by a simultaneous analytical method of SFE, cartridge column purification, followed by GC/MS determination. We achieved 70 to 120% recovery for more than 80% of the examined compounds.     

The use of alternative fluids in on-line supercritical fluid extraction – capillary gas chromatography

A key feature differentiating analytical supercritical fluid extraction (SFE) from conventional liquid extraction is the possibility of varying the solvent strength of a supercritical fluid to achieve selective extractions of specific target compounds, or functional classes of compound, from complex matrices. This can be accomplished by using supercritical fluids other than carbon dioxide, for example, sulfur hexafluoride, nitrous oxide, or sulfur hexafluoride-modified carbon dioxide. The use of these fluids will be demonstrated by the characterization of complex environmental and petroleum matrices by directly coupled SFE – capillary GC. On-line SFE-GC involves the decompression of pressurized extraction fluid directly into the heated, unmodified capillary split injection port of the chromatograph. This paper will also show how, by adjustment of the extraction temperature and pressure, SFE selectivity may be further enhanced.     

Effect of column diameter on efficiency in capillary supercritical fluid chromatography

Fused silica capillary columns with internal diameters from 100 to 25 μm were coated with SE-54 and evaluated under supercritical fluid chromatographic conditions using carbon dioxide as mobile phase. Experimental results compared well with theoretical predictions. At ten times the optimum mobile phase velocity and for a capacity factor, k of 3, efficiencies of 2300 to 5600 plates m^?1 were obtained for column diameters of 100 to 25 μm, respectively.     

Preparative supercritical fluid extraction of pyrethrin I and II from pyrethrum flower

A preparative supercritical fluid extraction system is described and was used with supercritical carbon dioxide to extract the active insecticide components pyrethrin I (PI) and pyrethrin II (PII) successfully from pyrethrum flower. A high-performance liquid chromatography method was developed and was used to separate and analyze the supercritical carbon dioxide extracts. Extraction efficiencies under several different extraction conditions were examined. Under the conditions examined, the most effective extractions of PI and PII (140 +/- 18 mg and 55 +/- 9 mg per 100 g of dry pyrethrum flower powder) were performed at 40 degrees C and 1200 psi. The results showed that extraction efficiencies of supercritical carbon dioxide are much better than those of n-hexane for pyrethrins I and II. During the extraction process, the most efficient extraction period was the first 3 h of the experiment.     

Anomalous effects of helium head pressure carbon dioxide in supercritical fluid chromatography and extraction

Helium head pressure carbon dioxide cylinders are commonly used to facilitate the delivery of liquid CO2 to supercritical fluid extraction and chromatographic pumps. It is usually tacitly assumed that the helium used to increase the delivery pressure of the CO2 cylinders is completely insoluble in liquid CO2 and thus remains isolated in the head space of the delivery cylinder. This assumption is invalid because up to 5 mol% helium can be entrained in the liquid CO2 delivered from helium head pressure cylinders. Significantly, contamination of liquid CO2 with even small amounts of helium can cause many unforeseen and usually deleterious effects in supercritical fluid chromatography and extraction schemes. The observed anomalies include decreased density of the fluid phase, irreproducible extraction and retention, ghost peaks, and even phase separation within the column or extraction vessel.     

Feasibility of ultra high performance supercritical neat carbon dioxide chromatography at conventional pressures

The implementation of columns packed with sub-2 μm particles in supercritical fluid chromatography (SFC) is described using neat carbon dioxide as the mobile phase. A conventional supercritical fluid chromatograph was slightly modified to reduce extra column band broadening. Performances of a column packed with 1.8 μm C18-bonded silica particles in SFC using neat carbon dioxide as the mobile phase were compared with results obtained in ultra high performance liquid chromatography (UHPLC) using a dedicated chromatograph. As expected and usual in SFC, higher linear velocities than in UHPLC must be applied in order to reach optimal efficiency owing to higher diffusion coefficient of solutes in the mobile phase; similar numbers of theoretical plates were obtained with both techniques. Very fast separations of hydrocarbons are presented using two different alkyl-bonded silica columns.     

Purification of OV-17 by supercritical fluid fractionation for fused silica capillary gas chromatography

Commercially available OV-17 was partitioned into a low and a higher molecular weight fraction by supercritical fluid extraction with carbon dioxide. This higher molecular weight fraction is more thermally stable than the original OV-17 due to its more viscous and gum-like nature. Based on the growing evidence in the literature that a deactivating agent for fused silica open tubular columns should be compatible with the stationary phase, a precoat of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane was applied prior to the static coating of high molecular weight OV-17. Fused silica OV-17 columns prepared in this fashion are stable up to 300°C.