Theoretical optimization of analyte collection in analytical supercritical fluid extraction

Summary Optimizing the extracted analyte collection step in analytical supercritical fluid extraction (SFE) is of key importance in achieving high analyte recoveries and extraction efficiencies. Whereas the extraction step in SFE has been well characterized both theoretically and experimentally; the analyte collection step after SFE has few theoretical guidelines, aside from a few empirical studies which have appeared in the literature. In this study, we have applied several theoretical approaches using experimental data to optimize analyte trapping efficiency in SFE. A vapour-liquid equilibrium model has been formulated to predict the trapping efficiency for extracted solute collection in a open collection vessel. Secondly, a simple solution thermodynamic model for predicting solute (analyte) activity coefficients in various trapping solvents has been shown to have utility in predicting collection efficiencies. Finally, effective trapping efficiency after SFE using sorbent media is related to the extent of analyte breakthrough on the sorbent-filled trap after depressurization of supercritical fluid. Using experimental data determined via physico-chemical gas chromatographic measurements (i. e., specific retention volumes), we have shown the relationship between analyte breakthrough volume off of the trapping sorbent and volume of depressurized fluid through the collection trap. The above theoretical guidlines should prove of value to analysts in designing and optimizing the best conditions for trapping analytes after extraction via analytical SFE. Names are necessary to report factually on available data; however the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the products to the exclusion of others that may also be suitable.     

Designing supercritical carbon dioxide extraction of rice bran oil that contain oryzanols using response surface methodology

This study examines the supercritical carbon dioxide (SC-CO(2)) extraction of oryzanols contained rice bran oil from powdered rice bran. The extraction efficiencies and concentration factors of oryzanols, free fatty acids and triglycerides in the SC-CO(2) extracts were determined. With top-flow type SC-CO(2) extraction the total oil yield was 18.1% and the extraction efficiencies of oryzanols and triglycerides were 88.5 and 91.3% respectively, when 2750 g CO(2 )was consumed during the extraction of 35 g rice bran powder. The concentration factors of oryzanols and triglycerides in SC-CO(2)-extracted oil were higher than in the Soxhlet n-hexane extracted oil. SC-CO(2) extractions indicated that pressure can be used more effectively than temperature to enhance the extraction efficiency and concentration factor of oryzanols. A two-factor central composite scheme of response surface methodology was employed to determine the optimal pressure (300 bar) and temperature (313 K) for increasing the concentration of oryzanols in the SC-CO(2) extracted oil.     

Considerations for analytical supercritical fluid extraction of sulfonyl ureas employing a modified fluid

Important considerations are discussed for analytical SFE method development employing methanol–modified carbon dioxide and solid-phase trapping. The focus of this study was to break the method development procedure into distinct steps so that the origins of low recoveries could be determined conclusively. Sulfonyl urea herbicides were used as probe analytes. Analyte solubility, analyte trapping, analyte trap removal (solid-phase), and extract analysis were all shown to be equally important in achieving quantitative SFE recoveries.     

Enrichment of the thymoquinone content in volatile oil from Satureja montana using supercritical fluid extraction

Supercritical fluid extraction (SFE) of the volatile oil from Satureja montana L. was performed under different conditions of pressure (90 and 100 bar), temperature (40 and 50°C), mean particle sizes (0.4, 0.6 and 0.8 mm) and CO₂ flow rate (0.8, 1.1 and 1.3 kg/h) to understand the influence of these parameters on the composition and yield of this oil. The results were compared with those obtained for the essential oil isolated by hydrodistillation (HD). The volatile and the essential oil were analysed by GC and GC‐MS. The main compounds are carvacrol (52.2–62.0% for HD vs. 41.7–64.5% for SFE), thymol (8.6–11.0% for HD vs. 6.0–11.3% for SFE), p‐cymene (6.9–12.8% for HD vs. 6.0–17.8% for SFE), γ‐terpinene (6.4–9.4% for HD vs. 2.3–6.0% for SFE) and β‐bisabolene (2.0–2.7% for HD vs. 2.2–3.5% for SFE). The major difference between SFE and HD was the relative amount of thymoquinone, an oxygenated monoterpene with important biological activities, which can be ten‐fold higher in volatile oil (1.6–3.0 for SFE vs. 0.2% for HD). The morphology of the glandular trichomes of S. montana and the effect of the grinding process on them was also evaluated by SEM.     

Specific extraction of chromium(VI) using supercritical fluid extraction

In some situations, it is no longer sufficient to give a total concentration of a metal. Instead, what is required to understand the potential toxicity of a sample is the concentration of metal species or oxidation state. When developing species specific methods, the major concern is that the integrity of the species ratio is not changed. In other words, the sample preparation or the analytical method will not convert metal ions from one oxidation state to another. Normal extraction techniques and chromatography methods have shown some tendencies to change species ratios. An ideal extraction method would extract the metal efficiently while retaining the metal's oxidation state. The properties of supercritical fluids should approach the ideal of retention of oxidation states. For example, the need for speciation of chromium is obvious since Cr(III) is considered an essential element while Cr(VI) is thought to be toxic and carcinogenic. This paper presents the results of a species specific extraction of Cr(VI) using two different carbamate derivatives as the chelator. Supercritical fluid extraction (SFE) coupled with a fluorinated dithiocarbamate and a methanol modifier allows extraction of 1 ppm Cr(VI) from a solid matrix with a recovery level of 88.4+/-2.57% using the NIST standard sample. The optimized conditions using the HP 7680 supercritical fluid extractor were: 0.1 ml of methanol, 0.05 ml of pure water, and 0.01 g of chelate via a saturation chamber.     

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.     

Grape seed oil extraction: Interest of supercritical fluid extraction and gas-assisted mechanical extraction for enhancing polyphenol co-extraction in oil

The aim of this study is to compare three oil extraction methods and to evaluate their efficiency for producing an oil rich in polyphenols. The three extraction methods are screw pressing, extraction by supercritical CO₂ percolation and the combination of these two processes (Gas-Assisted Mechanical Expression: GAME). Screw pressing is the most efficient process for producing grape seed oil with a high yield, but supercritical CO₂ process permits an increase of polyphenol co-extraction with oil. The GAME process allows extraction of more polyphenols than screw pressing and constitutes an interesting process considering oil yield.     

Optimization of supercritical fluid extraction of geniposidic acid from plantain seeds using response surface methodology

The process parameters of supercritical CO₂ (SCCO₂) plus modifer for the extraction of geniposidic acid from plantain seeds were studied using a Box–Behnken design. The effects of independent variables, that is, ethanol concentration (0–70%, ethanol:water, v/v), extraction pressure (10–30 MPa), and temperature (50–80°C) on the yield of geniposidic acid were evaluated. Results indicated that the data could be well fitted to a second-order polynomial model. The effects of ethanol concentration and temperature, as well as the interaction between ethanol concentration and temperature were significant (p < 0.05). The yield (8.9 mg/g) of modified SCCO₂ extraction at optimal conditions was compared with that obtained by Soxhlet extraction or ultrasound assisted extraction.     

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.     

Quantitative analysis of polymer additives in low density polyethylene using supercritical fluid extraction/supercritical fluid chromatography

Analysis of low concentration polymer additives has been a challenging problem. The commonly used methods of analysis involve the initial extraction of polymer additives with solvents, often in a Soxhlet apparatus, followed by liquid, size exclusion, or gas chromatography. This paper describes the on-line super-critical fluid extraction (SFE)-supercritical fluid chromatographic (SFC) determination of different additives from low density polyethylene. Cryogenic collection was used as an interface between SFE and SFC to focus the extraction eluate before transfer to an analytical SFC column for quantitative analysis.     

Optimization of Algerian rosemary essential oil extraction yield by supercritical CO2 using response surface methodology

The present study deals with the determination of optimal values of operating parameters such as temperature and pressure leading to the best yield of a supercritical CO₂ extraction of essential oil from local rosemary plants, using the response surface methodology (RSM). The maximum of essential oil recovery percentage relative to the initial mass of leaf powder was 3.52 wt%, and was obtained at 313 K and 22 MPa.A second-order polynomial was used to express the oil recovery and the calculated mass of recovered oil using the RSM was very close to the experimental value, confirming the reliability of this technique.The chemical composition of the Algerian rosemary oil under the obtained optimal conditions (313 K and 22 MPa), determined by GC–MS analysis, revealed the presence of camphor (major compound) (52.12%), 1,8-cineole (9.65%), camphene (7.55%), α-pinene (6.05%), borneol (3.52%), aroma dendrene (2.11%), verbenone (1.97%), α-caryophyllene (1.71%), and others.     

Analytical-process supercritical fluid extraction: a synergestic combination for solving analytical and laboratory scale problems

Identical principles govern the theory and application of supercritical fluid extraction (SFE) whether they are applied in the field of chemical engineering or analytical chemistry. We have used these principles to develop instrumentation and methodology that can be used to solve a wide range of analytical and laboratory problems. The development of larger scale extractors for analytical use will be presented, including modules which allow the extraction of larger samples, multiple samples simultaneously, and highly viscous materials. Key components in the design of these extractors, such as fluid delivery systems, collection devices, and cosolvent addition schemes, will also be described. This equipment and the components have been integrated into a laboratory-wide extraction and processing system.     

Pressurized fluid extraction of essential oil from Lavandula hybrida using a modified supercritical fluid extractor and a central composite design for optimization

Essential oil components were extracted from lavandin (Lavandula hybrida) flowers using pressurized fluid extraction. A central composite design was used to optimize the effective extraction variables. The chemical composition of extracted samples was analyzed by a gas chromatograph-flame ionization detector column. For achieving 100% extraction yield, the temperature, pressure, extraction time, and the solvent flow rate were adjusted at 90.6°C, 63 bar, 30.4 min, and 0.2 mL/min, respectively. The results showed that pressurized fluid extraction is a practical technique for separation of constituents such as 1,8-cineole (8.1%), linalool (34.1%), linalyl acetate (30.5%), and camphor (7.3%) from lavandin to be applied in the food, fragrance, pharmaceutical, and natural biocides industries.     

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.     

Improved supercritical fluid extraction of sulphonamides

Summary Different ways used for enhancing the yield of sulphonamides leached from solid supports are reported. Supercritical CO₂ and methanol-modified CO₂ were used as extractants of the target analytes and the impregnation of the solid sample with buffer, derivatization of the analytes and ion-pair formation were assessed. Only the sulphonamide/tetramethyl-ammonium ion-pairs are quantitatively extracted from the solid supports using pure supercritical CO₂, while the other modifications and the presence of a cosolvent lead to recoveries lower than 30% for most of the analytes. Individual separation/quantitation of the analytes was performed off-line using a liquid chromatograph.     

Some applications of supercritical fluid extraction

Supercritical fluid extraction (SFE) exploits the solvation power of fluids at temperatures and pressures close to their critical point. Use of SFE with supercritical CO₂ is reported for the extraction of caffeine and quinine from various plant materials and of morphine from serum. Results are compared with those obtained by extractions with subcritical methanol and tetrahydrofuran, normal organic Soxhlet extractions and solid-phase extraction.     

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.