Analysis of mono-, di-, and triglycerides by capillary supercritical fluid chromatography

The separation of mixed mono-, di-, and triglycerides by capillary supercritical fluid chromatography is described. The separations were performed at low operating temperatures, using a carbon dioxide mobile phase, a conventional flame ionization detector, and two different stationary phases, DB-5 (95% dimethyl-(5%)-diphenylpolysiloxane) and DB-225 (50% cyanopropyl-methyl-(50%)-methylphenylpolysiloxane). Because the separations were performed at low operating temperatures, no thermal degradation of the glycerides was observed. Even under these mild operating conditions, trinervonin, a triglyceride having a molecular weight over 1100 amu, was readily eluted. When rapid pressure programming of the carbon dioxide mobile phase was employed, trinervonin was eluted in less than two minutes. On DB-5, the mono-, di-, and triglycerides eluted in order of increasing molecular weight. A graph of t′_r (on DB-5) versus molecular weight is linear. When DB-225 was used as the stationary phase, triglycerides eluted in the order of increasing unsaturation. Thus, the order of elution on DB-225 was tristearin, triolein, trilinolein, and trilinolenin.     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

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.     

Current technological challenges in capillary supercritical fluid chromatography

In cases where high efficiency is required to resolve complex mixtures of either thermally labile or nonvolatile organic compounds, capillary supercritical fluid chromatography may be the most desirable analytical method. While great strides in this new technology have been made over the last few years, several problem areas are requiring increased attention. These include sample introduction systems, pressure reduction at the end of the column, column stability in various supercritical mobile phases, and migration of polar solute molecules. This paper describes the state-of-the-art in capillary SFC with emphasis on the progress made and future needs in the solutions to these specific problems.     

Low flow rate modifier addition in packed capillary column supercritical fluid chromatography

A new method to accurately deliver small amounts (0.5 to 20 mol%) of modifier into CO₂ was used to study the effects of three different modifiers (methanol, water, and formic acid) in packed capillary column SFC. The method allows the use of different modifiers, with minimal instrument modification. The effects of the different modifiers at different concentrations on retention and peak shape are shown by analyzing a polarity test mixture and a sample of free fatty acids.     

Splitless injection in capillary supercritical fluid chromatography

A splitless injection technique, allowing 0.5 μl injections on 50 μm i.d. columns, has been developed.     

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.     

Retention in coupled capillary column supercritical fluid chromatography with lipids as model compounds

Summary We have investigated to which extent retention data, acquired on single capillary columns, can be used for predicting retention factors in a coupled column system. For this purpose we utilized a model mixture of 18 lipid components with widely different vapor pressures and polarities. The sample was chromatographed on two columns, SB-biphenyl-30 (70% methyl-30% biphenylpolysiloxane) and SB-cyanopropyl-50 (50% methyl-50% cyanopropylsiloxane). Experimental retention factors, acquired in coupled column systems with two columns connected in different order, were thus compared with values calculated from runs on each single column. The agreement between calculated and experimental values generally was better than 5% without any pressure drop correction.To study the possibility of predicting retention behavior in a wide pressure range from a limited number of experiments, we also investigated the relation between solute retention and mobile phase density. We found that all data could be fitted to second order equations, which gives the possibility to optimize the resolution with respect to pressure from a limited number of runs at different pressures.     

Supercritical fluid chromatography with a slurry-packed capillary column

A versatile system with a slurry-packed capillary column was developed for supercritical fluid chromatography, which is capable of programming both inlet and outlet pressure independently, as well as using a restrictor to apply back pressure. This system revealed the relationships between pressure drop, flow rate, and linear velocity in pressure-programmed supercritical fluid chromatography. In the restrictor system, both the pressure drop and the flow rate increased almost linearly with inlet pressure, while under conditions of constant pressure drop characteristic behavior was observed which depended on the density-viscosity relationships of supercritical fluid. Resolution in the separation of polysiloxane oligomers was found to be increased by increasing the ratio of pressure drop to pressure-programming rate, although the sensitivity decreased due to the increase in peak volume. The system controlling both inlet and outlet pressure has distinct advantages over the restrictor system controlling both inlet and outlet pressure has distinct advantages over the restrictor system in practical in practical operations.     

Liquid crystal stationary phases for gas chromatography and supercritical fluid chromatography

Novel monomeric and polymeric liquid crystalline compounds were synthesized as stationary phases for gas chromatography (GC) and supercritical fluid chromatography (SFC). Monomeric liquid crystalline compounds were used in packed column gas chromatography for the separation of isomeric aromatic compounds and insect sex pheromones. Liquid crystalline polymers possess long nematic ranges and a uniform coating was easily achieved in glass and fused silica capillaries, which could stand temperatures up to 250°C in GC and pressures of 200 MPa at 160°C in SFC. The columns provide excellent selectivity and resolution for fused ring aromatic compounds such as the isomers anthracene and phenanthrene or triphenylene and chrysene.     

Temperature programming elution in capillary supercritical fluid chromatography

Summary Effects of column temperature on the retention behaviour of aromatic hydrocarbons and dialkyl phthalates were investigated in capillary supercritical fluid chromatography (SFC) with carbon dioxide as the mobile phase. Negative temperature programming could partly replace pressure programming. Positive temperature programming was applicable to solutes with proper volatility, in which gas chromatography-like retention mechanism (partition process) was involved.     

On-line multidimensional supercritical fluid chromatography/capillary gas chromatography

A new analytical technique combining on-line supercritical fluid chromatography with capillary gas chromatography has been developed. The supercritical fluid sample effluent is decompressed through a restrictor directly into a conventional capillary gas chromatographic injection port. This technique allows for not only direct (100%) sample transfer from the supercritical fluid chromatograph to the gas chromatograph but also for selective or multi-step heartcutting of various sample peaks as they elute from the supercritical fluid chromatograph. Heartcut times are determined by monitoring the responses from the flame ionization or ultraviolet absorbance detectors on the supercritical fluid chromatograph. This report describes the operational setup and provides the results of heartcut reproducibility experiments using normal hydrocarbon and aromatic test mixtures. Results from studies where operational parameters were varied, such as GC injector temperature, will also be provided. The potential usefulness of this new technique for selective heartcutting will also be demonstrated using complex hydrocarbon streams.     

Fused silica capillary micro-packed columns in gas chromatography

Summary Flexibility, strength and adsorption inertness of fused-silica capillaries permits their extensive application for the preparation of micro-packed columns in gas chromatography. Decreasing the column diameter (from 0.5 to 0.15 mm) and the diameter of the sorbent particles (from 100 to 5 μm) results in a marked reduction of the height equivalent to a theoretical plate (HETP), as well as in diminishing the dependence of the HETP on the carrier gas flow rate. The chromatographic characteristics of fused-silica capillary micro-packed columns and open-tubular columns are compared. The fused-silica capillary micro-packed column can be used to advantage for performing rapid and trace analyses and have been shown to be adapted for application in gas-solid chromatography. Separation of organic and inorganic compounds on fused-silica capillary micro-packed columns is illustrated by practical examples. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Applications of packed and capillary supercritical fluid chromatography in the separation of tocochromanols

Tocochromanols consisting of tocopherols and tocotrienols, is collectively known as vitamin E. Similarity in their structures, physical and chemical properties rendered the tocochromanols to be subject of chromatography interest. Supercritical fluid chromatography is a highly efficient tool for the separation and analysis of tocochromanols. Separation and analysis of tocochromanols using supercritical fluid chromatography had been carried out in the past using capillary or packed columns. Each of these techniques offer their own advantages and drawbacks. Besides being used for analysis, packed column supercritical fluid chromatography found applications as a purification and content enrichment tool. Emergence of new equipment and stationary phase technologies in recent years also helped in making supercritical fluid chromatography a highly efficient tool for the separation and analysis of tocochromanols. This paper gives an insight into the use of capillary and packed columns in supercritical fluid chromatography for the separation and/or analysis of tocochromanols. The types of stationary phase used, as well as chromatographic conditions are also discussed.     

Simultaneous coupling of capillary supercritical fluid chromatography and high temperature glass capillary gas chromatography to a mass spectrometer

The coupling of glass capillary supercritical fluid chromatography to a high temperature GC/MS system via a micrometeradjustable glass capillary interface including an integrated pressure restrictor is described. With this coupling device, both complementary capillary chromatographic methods retain their full independence and flexibility. It is shown that in supercritical fluid chromatography glass fulfils all the requirements of a suitable support material. The preparation of narrow bore glass capillary columns (0.06 mm i.d.), coated with chemically bonded and crosslinked fluids with a film thickness of about 0.6 μm, which exploit the merits of OHterminated polysiloxanes as stationary phases is discussed. The application of glass capillary SFC is demonstrated and compared with examples given in the literature.     

The analysis of lubricating oil additives by supercritical fluid chromatography with packed and open tubular capillary columns

Lubricating oil additives have been analyzed by supercritical fluid chromatography on open tubular and packed capillary columns. Carbon dioxide and modified carbon dioxide were used as mobile phases and detection was accomplished by flame ionization and micro UV. Rapid and efficient analysis of the lubricating oil additives was demonstrated.