Application of capillary supercritical fluid chromatography to the analysis of a middle distillate fuel

Summary The application of capillary supercritical fluid chromatography (SFC) to the analysis of a middle distillate fuel is described. Small diameter (50m i.d.) fused-silica capillary columns coated with crosslinked 50% phenyl polymethylphenyl siloxane provided high separation efficiency and good compatibility with flame ionization detection. High resolution separations of the chemical class fractions obtained by adsorption chromatography on alumina were obtained using carbon dioxide as the supercritical mobile phase and simple pressure programming techniques. In addition to the less polar fuel components, supercritical carbon dioxide allowed chromatography of the nitrogen-containing polycyclic aromatic hydrocarbon fraction and the hydroxylated polycyclic aromatic materials.     

Application of supercritical fluid extraction and supercritical fluid chromatography to the production of taxanes as anti-cancer drugs

The supercritical fluid extraction (SFE) of taxicin from the dried needles of the English yew tree, Taxus baccata is described. Analysis by supercritical fluid chromatography (SFC) and proton NMR spectroscopy was used to confirm identity and purity. The extraction efficiency of SFE is comparable with that obtained using liquid solvents. Such taxanes may be used semi-synthetically to prepare potential anti-cancer drugs.     

Rapid analysis using capillary supercritical fluid chromatography

Capillary supercritical fluid chromatography (SFC) is proving to be a viable and useful separation method for thermally labile and nonvolatile materials. As with other capillary chromatographic techniques, very fast separations can be accomplished by sacrificing total efficiency and optimizing the conditions for rapid analysis. This is achieved using short, small-bore capillary columns, increased mobile phase linear velocities and very fast pressure programming rates. These principles are demonstrated for the rapid separation of selected component systems.     

Trace analysis of agrochemicals by supercritical fluid chromatography

Capillary supercritical fluid chromatography was performed using solvent-vented injection in conjunction with a thermionic ionization detector. Mixtures of organo-nitrogen and phosphorus containing agrochemicals were chromatographed and detection of low picogram quantities was observed.     

High-resolution analysis of polyprenols by supercritical fluid chromatography

A high-resolution analysis of polyprenol mixtures was achieved by supercritical fluid chromatography (SFC). The separation of polyprenols was examined on an octadecylsilane-packed column with liquid carbon dioxide as the mobile phase and ethanol as modifier. Using this chromatography system, the resolution of separation (Rs) between octadecaprenol (prenol 18) and nonadecaprenol (prenol 19) was two times higher than that using conventional reversed-phase high-performance liquid chromatography. Our SFC technique allows the advantage of baseline separation of polyprenol samples containing hydrophobic components such as terpenes or fatty acids that are unfavorable for good separation. This method is very useful for the analysis of structurally close polyprenol analogues of rubber plant metabolites.     

Industrial applications of supercritical fluid chromatography: polymer analysis

Summary Polymers can be difficult to fully characterize by conventional chromatographic methods [i.e., gas chromatography (GC), high performance liquid chromatography (HPLC) and size exclusion chromatography (SEC)] due to temperature instability, detector incompatibility, nonvolatility, molecular weight considerations or insufficient chromatographic efficiency. Capillary supercritical fluid chromatography (SFC) offers several advantages for polymer analysis. Complex distributions can be resolved, low temperatures can be used and individual oligomers can be detected, allowing differences in molecular weight distributions to be quantitatively and qualitatively measured. In this paper, results will be shown for the analysis of various types of polymers demonstrating how changes in chromatographic parameters affect the analysis

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Industrielle Anwendungen der Chromatographie mit überkritischen fluiden Phasen: Polymeranalyse

     

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.     

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.     

Capillary supercritical fluid chromatography of limonoids

Capillary supercritical fluid chromatography (SFC) with carbon dioxide as the mobile phase has been used to separate a mixture of limonoid standards. Chromatographic conditions were optimized to enable analysis of plant extracts. The seed of Aphanamixis polystacha (Meliaceae) and the stem bark of Harpephyllum caffrum (Anacardiaceae) were extracted with hexane and the extracts were analyzed by SFC to demonstrate the potential of the technique as a screening tool. SFC analysis indicated the presence of limonoids in the hexane extract of the bark of Entandrophragma delevoyii (Meliaceae). One limonoid and two protolimonoids isolated from the extract were separated by SFC.     

Application of packed column supercritical fluid chromatography to the simultaneous determination of seven anticonvulsant drugs

Studies of speed, resolution, and selectivity have shown that packed column supercritical fluid chromatography (PCSFC) is a viable technique for the isocratic, isothermal and isobaric separation of seven anticonvulsants, viz., phenobarbitone, phenytoin sodium, phethenylate sodium, nitrazepam, clonazepam, carbamazepine, and primidone, and their simultaneous estimation. The drugs were eluted from a JASCO, RP-C₁₈ (250×4.6 mm) 10 μ packed column with a binary mobile phase of carbon dioxide and methanol, using ibuprofen as the internal standard. The effect of pressure, temperature, modifier concentration, and the rate of flow of CO₂ on retention and selectivity of all the analytes were studied and the parameters optimised. Without methanol in the mobile phase none of the solutes eluted. Changing modifier concentration was the most effective physical parameter for changing retention and selectivity. The analytes were detected using a UV detector at 215 nm. An arbitrary mixture of eight components was baseline resolved in 7 min. The study includes a successful attempt at quantification of the drugs. Chromatographic and analytical figures of merit have been listed. The present work holds promise for a possible replacement of HPLC with SFC for the separation and assay of drugs of different families.     

Retention in capillary supercritical fluid chromatography

Supercritical fluid chromatography (SFC) sometimes exhibits GC-like behavior and sometimes LC-like behavior, depending on conditions. However, it is not always clear whether one of these types of behavior, or a combination, operates for a particular set of conditions for every solute in a mixture. For example, some components may be partitioned mostly by their vapor pressures, while others, in the same mixture, are partitioned predominantly by solvent-like properties of the mobile phase. Plots of retetion (as log of the capacity factor) vs. reciprocal temperature at constant pressure reveal a clear change in the character of the separation of well-behaved solutes. A thermodynamic explanation of the observed behavior is given, based on the assumption that partitioning is controlled by the heats of solution of solute in the mobile and stationary phases. A model of SFC retention as it deviates from pure-GC behavior on the same column is presented.     

Qualitative supercritical fluid extraction coupled to capillary gas chromatography

The usefulness and ease of utilizing supercritical fluid extraction (SFE) directly coupled to capillary gas chromatography (GC) as quantitative or qualitative analytical problem-solving tools will be demonstrated. As an alternative to conventional liquid solvent extractions, SFE presents itself as a means to achieve high extraction efficiencies of different compounds in complex solid matrices in very rapid tims frames. Moreover, SFE has an additional advantage of being able to achieve distinct extraction selectivities as a function of the solubilizing power of the supercritical fluid extracting phase. For on-line SFE/GC, the extraction effluent is directly transferred to the analytical chromatograph. On-line SFE/GC involves the decompression of pressurized extraction effluent directly into a heated, unmodified capillary split injection port of the GC. In this respect, SFE introduction into GC can be used as an alternative means of GC injection, comparable to such modes of injection as pyrolysis and thermal desorption. This paper will show applications of SFE/GC where mass spectrometric detection together with flame ionization detection was used for component identification from environmental, tobacco, and petroleum matrices.     

Mobile phases for supercritical fluid chromatography

Summary Several liquids have been tested under supercritical conditions for their suitability in chromatographic separations. Experimental pressures were up to about 150 atm, temperatures to 300°C; stationary phases of differing polarity were used. Stability under all experimental conditions is shown by cyclohexane, di-i-propylether, benzene, tetrahydrofuran and ethylacetate, while halogenated alkanes, branched alkanes, ketones and acetonitrile decompose in some cases.     

Sampling considerations in supercritical fluid chromatography

Summary Packed column supercritical fluid chromatography, like HPLC, utilizes a sample loop to introduce materials onto the column for analysis. Unlike HPLC the mobile phase in SFC cannot be used to dissolve the sample. In practice, this causes a solvent peak, which can create a problem in the chromatographic interpretation. This paper describes one approach to solving this problem. A valving scheme is used to extract materials with the supercritical CO₂ mobile phase and introduce them onto the column with no external handling. The viability of this method is demonstrated and separations of the CO₂ extracts for several materials are shown on various columns. Comparisons are made for coal and coffee extracts using this on-line method and conventional off-line CH₂Cl₂ extracts. Advantages of the on-line procedure as they apply to chromatography and high information detectors are also discussed.     

Isocratic networks in supercritical fluid chromatography

For chromatography with supercritical fluids (SFC), the dependence of the capacity ratios k′ and of the mean resolution R_m on temperature and pressure is presented as a three-dimensional diagram. A sufficient number of test chromatograms were run for the diagram to lead to an isocratic network in form of a curved surface. The isocratic network possesses a characteristic shape and contains all information about the temperature and pressure dependence of k′ and R_m for a given volume flow rate and chromatographic system. The specific system studied comprised pentane as the mobile phase, unmodified silica as the stationary phase, and a set of four polycyclic hydrocarbons as the test mixture. The isocratic net of this system allows interpolation of k′ and R_m for any temperature and pressure. Together with similar experimental data from other systems, this allows qualitative forecasts about the isocratic nets of other systems.