Methanol-modified Supercritical Carbon Dioxide Research Articles

Calculation of the Solubility of Ortho-, Meta-, and Para-Hydroxybenzoic Acids in Pure and Methanol-Modified Supercritical Carbon Dioxide Based on Data from Molecular Dynamics

Calculation of the Solubility of Ortho-, Meta-, and Para-Hydroxybenzoic Acids in Pure and Methanol-Modified Supercritical Carbon Dioxide Based on Data from Molecular Dynamics

Hydrogen-Bonded Complexes of p-Hydrobenzoic Acid and Its Derivatives with a Polar Cosolvent in Supercritical Carbon Dioxide

The results of numerical modeling of p-hydroxybenzoic acid, methylparaben, and propylparaben solutions in methanol-modified supercritical carbon dioxide were presented. The composition, structure, and formation energy of the solute–cosolvent hydrogen-bonded complexes were determined. The duration of the existence of hydrogen bonds via individual paraben atoms was evaluated based on the data of Car–Parrinello ab initio molecular dynamics simulation, and the potential of mean force of interaction with methanol was calculated taking into account the medium. It was shown that, despite the presence of several potential centers of specific interaction, p-hydroxybenzoic acid and its derivatives form hydrogen bonds mainly via carboxyl and hydroxyl protons, respectively.

Classical and ab initio molecular dynamics simulation of p-coumaric acid in methanol-modified supercritical carbon dioxide

Classical and ab initio molecular dynamics simulation of p-coumaric acid in methanol-modified supercritical carbon dioxide has been performed. Structural properties such as radial distribution functions, coordination numbers, and average numbers of hydrogen bonds were obtained. Vibration density of states was calculated from velocity autocorrelation functions. The redshift in the frequency of the OH stretching mode for hydroxyl and carboxyl groups of the solute in fluid compared with the same values for the p-coumaric acid in gas phase is an evidence for H-bond formation. Analysis of the hydrogen bond lifetimes indicates that p-coumaric acid forms stable hydrogen bonds with methanol through hydroxyl and carboxyl protons. At the same time, the longest period of the absence of hydrogen bond is observed for carbonyl oxygen.

Selective solvation in cosolvent-modified supercritical carbon dioxide on the example of hydroxycinnamic acids. The role of cosolvent self-association

The study of the selective solvation of hydroxycinnamic acids (para-coumaric, caffeic) by a polar cosolvent (acetone, methanol) in supercritical carbon dioxide at T = 328 K, ρ = 0.772 g/cm3 has been carried out using the molecular dynamics and quantum-chemical calculations. It has been shown that the selective solvation of the solute occurs by the formation of hydrogen-bonded complexes with a cosolvent. The formation of hydrogen-bonded complexes with two or more cosolvent molecules is most likely in methanol-modified supercritical carbon dioxide even at a low concentration of the methanol, whereas the formation of a complex with one cosolvent molecule is preferred in the acetone-modified fluid. If the cosolvent is capable of self-association in supercritical carbon dioxide (methanol), then hydrogen-bonded cosolvent clusters are grouped around the solvate complexes even at low concentration of it. The number of molecules in such clusters can reach 10, although methanol associates consist of no more than three molecules in the fluid bulk.

Orthogonal array design for the optimization of supercritical fluid extraction of baicalin from roots of Scutellaria baicalensis Georgi

Supercritical fluid was used to extract baicalin from the roots of Scutellaria baicalensis Georgi. An orthogonal array design (OAD), OA(9)(3(4)), was employed as a chemometric method for the optimization of the supercritical fluid extraction of baicalin from the herbal medicine. Four parameters, namely, modifiers, temperature and pressure of supercritical fluid, and the dynamic extraction time, were studied and optimized by a three-level OAD in which the interactions between the parameters were neglected. Determinations of the extracts were performed by high-performance liquid chromatography. The effects of parameters were studied using analysis of variance. The results showed that selection of the modifier was the main factor in attaining higher yields of baicalin. While the other three factors had some effect on the extraction of the compound, the effect was much less than that of the modifiers. 1,2-Propanediol-modified supercritical fluid was more effective than 95% ethanol-modified supercritical carbon dioxide or methanol-modified supercritical carbon dioxide for the extraction of baicalin from the solid matrix. Finally, experimental conditions were proposed which can provide the highest extraction yield with respect to the considered factors.

Effect of system variables involved in packed column supercritical fluid chromatography of stavudine taken as model analyte using response surface methodology along with study of thermodynamic parameters

A multifactor optimization technique is successfully applied to study the effect of simultaneously varying the system variables on feasibility of stavudine analysis by packed column supercritical fluid chromatography (PC-SFC). The effect of simultaneously varying the pressure, temperature and modifier concentration was studied to optimize the method in order to obtain excellent chromatographic figures of merit. The method is based on isocratic elution using methanol-modified supercritical carbon dioxide as the mobile phase at the flow rate of 3.0 ml/min through a JASCO Finepak SIL-5, ODS [C 18 (5 μm, 25 cm × 4.6 mm, i.d.)] column support using photodiode array detection. The optimal conditions were determined with the aid of the response surface methodology using 3 3 factorial designs. From the response surface graphs optimum regions were selected to be +1, −1, and +1 for temperature (60 °C), pressure (20 MPa) and percent modifier concentration (17.81%, v/v), respectively. Linearity dynamic range was found to be in the range of 2.0–150.0 μg/ml with significantly high value of correlation coefficient. The method was validated for precision, robustness and recovery to assess the viability of the established method. The chromatographic limit of detection and quantitation were 0.80 and 1.50 μg/ml respectively. The method has been successfully used to analyze commercial dosage form to assess the chromatographic performance of SFC system which was found to be 99.91% ± 1.62. The present work briefs the thermodynamic applications of PC-SFC with an emphasis on the results of stavudine. The foremost of such applications is the determination of solute diffusion coefficient in supercritical mobile phase by Taylor–Aris peak broadening technique.

Measurement and correlation of solubility of Acid Red 57 in supercritical carbon dioxide by ion-pairing with hexadecyltrimethylammonium bromide

Solubility of C.I. Acid Red 57 (AR57) in supercritical carbon dioxide was measured by ion-pairing with hexadecyltrimethylammonium (HDTMA) bromide. The solubility measurements of AR57 and AR57-HDTMA in supercritical carbon dioxide without/with methanol as a modifier solvent were carried out at the temperature range from 35 to 75 °C and for pressures from 250 to 325 bar. The solubility of AR57 and AR57-HDTMA was examined in terms of pressure and temperature of supercritical carbon dioxide. Even though Acid Red 57 is insoluble both in supercritical carbon dioxide and methanol-modified supercritical carbon dioxide, AR57-HDTMA can easily dissolve in methanol-modified supercritical carbon dioxide. The hydrophobic ion-pairing of HDTMA provides a possibility to dissolve a hydrophilic dye in supercritical carbon dioxide. A semi-empirical equation was used to correlate the obtained experimental solubilities of AR57-HDTMA by means of the density of carbon dioxide in methanol-modified supercritical carbon dioxide.

Supercritical fluid extraction of sinomenine from Sinomenium acutum (Thumb) Rehd et Wils

Supercritical carbon dioxide, with and without a methanol modifier, was used to extract sinomenine from Sinomenium acutum (Thumb) Rehd et Wils. Sinomenine determinations were carried out using high-performance liquid chromatography (HPLC). The results show that the yield obtained after 2.5 h extraction with methanol-modified supercritical carbon dioxide was the highest (7.47 mg/g), while that obtained with only supercritical carbon dioxide was the lowest (0.17 mg/g). The recovery obtained with supercritical carbon dioxide, with and without a methanol modifier, could not be increased greatly by the method of the alkalinization of sample. Higher recoveries were obtained than extraction using methanol in Soxhlet extractor.

Extraction of Tanshinone IIA from Salvia miltiorrhiza bunge using supercritical fluid extraction and a new extraction technique, phytosol solvent extraction

Supercritical carbon dioxide with and without a methanol modifier has been compared with a new portable cold extraction technique, phytosol solvent extraction (PSE), for the extraction of Tanshinone IIA from Salvia miltiorrhiza bunge. High-performance liquid chromatography was used to analyse the extracts. The results show that the yield extracted by 10% methanol-modified supercritical carbon dioxide was the highest (0.038%, w/w) and the yields extracted by supercritical carbon dioxide at 60°C and 250 kg/cm 2 and phytosol solvents (A,B and D) were similar (0.029–0.032%, w/w).

A comparative study of the composition of biomarkers in SFE and solvent extracts of oil shales

A comparative investigation of the composition of polycyclic biomarkers (steranes and triterpanes) in the extracts from the Paleocene Boltysh oil shale obtained by methanol-modified supercritical carbon dioxide and conventional Soxhlet chloroform extraction was carried out using computerized GC-MS. The extracts are similar in the geochemical parameters calculated on the basis of the stereoisomeric composition of steranes and triterpanes which: (1) are indicative of lacustrine sedimantary organic matter (OM); (2) show the higher plant contribution to the mainly alginitic OM of oil shale; and (3) are characteristic of low-mature OM.

Determination of Antifungals in Rodent Diet by Supercritical Fluid Extraction Followed by Packed Column Supercritical Fluid Chromatography with Ultraviolet Detection

Supercritical fluid extraction (SFE) followed by packed column supercritical fluid chromatography with ultraviolet detection was evaluated as a quantitative method for determining 4 antifungals (fluconazole, tioconazole, hexaconazole, and UK-47,265) in rodent diet. Chromatography was achieved with a cyano-bonded silica column, UV detection at 210 nm, and methanol-modified supercritical carbon dioxide as mobile phase. The effects of modifier concentration, temperature, and column pressure on antifungal retention time was studied. Off-line SFE was optimized at 2 spike levels, ranging from 0.5 to 10 g/kg, for each of the 4 antifungals. Average recoveries ranged from 79.0% for UK-47,265 to 96.5% for hexaconazole. Overall, the procedure provides a suitable method for analyzing antifungals in spiked rodent diet.

The Extraction and Determination of Azadirachtin from Soil and Insects by Supercritical Fluid Extraction

Abstract Azadirachtin is a powerful anti-feedant and insect growth-disrupting compound. A primary problem with the utilization of classical extraction techniques for determining azadirachtin is the high hydrophilicity of the compound. Further, since determination by high-performance liquid chromatography (HPLC) requires measuring absorbance at 214 nm, use of methanol for extraction requires a solvent exchange since methanol absorbs in this region. This paper demonstrates the use of supercritical fluid extraction for determination of azadirachtin residues. Methanol-modified supercritical carbon dioxide is used to extract azadirachtin from soil and Japanese beetle adult and larval forms. Greater than 80% of fortified material was recovered at spike concentrations of 1 to 2 µg/g. Using this procedure azadirachtin was determined to be field stable for less than 3 months. Azadirachtin was also successfully extracted from insects showing recovery levels of 75% and greater. The inability of modified supercritical carbon dioxide to cross the insect cuticle was also demonstrated.

Influence of pesticide–soil interactions on the recovery of pesticides using supercritical fluid extraction

The role of soil organic matter on the recovery of two classes of pesticides and two classes of herbicides using supercritical carbon dioxide has been investigated. Initial studies from spiked Celite indicated that the more polar herbicides required the addition of 10% methanol modified supercritical carbon dioxide to affect extraction. Whereas the relatively non-polar organochlorine pesticides (OCPs) could be extracted using supercritical carbon dioxide only, the moderately polar organophosphorus pesticides (OPPs) required 5% methanol-modified supercritical carbon dioxide to affect quantitative recovery. When using these supercritical conditions each class of pesticide or herbicide was extracted from a slurry-spiked soil. The effects on the recovery from soils with a range of organic matter were noticeable for both classes of pesticides, particularly when the organic matter was at its highest (35%). The role of the modifier was found to be critical in affecting recovery of the polar OPPs and herbicides. The soil-pesticide interaction from these slurry spiked soils could be negated if excess modifier (10%) was added to the supercritical carbon dioxide. Matrix interactions were most severe when no modifier was added (recoveries of OCPs from soil were approximately 50%).

Analysis of Organophosphorus Pesticides in Rice by Supercritical Fluid Extraction and Quantitation Using an Atomic Emission Detector

A rapid and sensitive method for the detection and quantitation of organophosphorus pesticides in rice has been developed. It uses extraction with methanol-modified supercritical carbon dioxide followed by quantitation by a gas chromatograph equipped with an atomic emission detector operating in the phosphorus and sulfur modes. Evaporative displacement of the collection solvent during the supercritical fluid extraction stage allows quantitation of the analyte down to 10 ng/g without any intermediate concentration steps.

Supercritical fluid extraction in the determination of tobacco-specific N-nitrosamines in smokeless tobacco.

A new approach to the analysis of the carcinogenic, tobacco-specific N-nitrosamines (TSNA) in moist snuff tobacco is based on the extraction of tobacco with methanol-modified supercritical carbon dioxide. Extracted TSNA are trapped across a glass cartridge filled with Tenax GR, from which they are subsequently released by thermal desorption and analyzed by capillary gas chromatography with a thermal energy analyzer. The analytical recoveries for the major TSNA range from 83 to 98%; the detection limits are below 2 ng/g. The methodology is fast, reproducible, highly selective, and sensitive. The supercritical fluid extraction (SFE) releases up to 7 times more of the highly carcinogenic 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) from tobacco than has been determined after conventional solvent extraction. Studies have confirmed that this is not an artifact. In contrast, the cyclic N-nitrosamines, N'-nitrosonornicotine, N'-nitrosoanabasine, and N'-nitrosoanatabine, showed no significant quantitative differences whether determined by the SFE method or the conventional solvent extraction method.