Mustafa Demirbüker

Argentation supercritical fluid chromatography for quantitative analysis of triacylglycerols

A method for quantitative analysis of neutral lipids has been developed. Four different techniques have been combined for this purpose—supercritical fluid chromatography (SFC), silver ion chromatography, packed microcolumns and miniaturized evaporative light-scattering detection (ELSD). The development and optimization of the method are discussed. The separation of a series of vegetable, fish and hydrogenated oils was demonstrated. Application of eluent composition programming resulted in excellent separation of complex samples. Packed microcolumn argentation SFC provides at least as high a separation power as corresponding high-performance liquid chromatography methods. The combination of packed microcolumn SFC and miniaturized ELSD constitutes a powerful analytical system for the quantitative analysis of triacylglycerols.

Separation of triacylglycerols by supercritical-fluid argentation chromatography

Abstract Microcolumns packed with a silica-based cation exchanger were used to separate triacylglycerols in vegetable oils. A supercritical mobile phase consisting of carbon dioxide, acetonitrile and isopropanol was used. Argentation chromatography results in separation according to the number of double bonds; in this work, separation was also obtained according to chain length and the nature of the double bonds. Full separation of molecular species of triacylglycerols in the investigated oils could be obtained after fractionation in reversed-phase liquid chromatography.

Separation of unsaturated fatty acid methyl esters by packed capillary supercritical fluid chromatography: Comparison of different column packings

Abstract Packed capillary supercritical fluid chromatography with ultraviolet detection was applied to the separation of methyl esters of unsaturated fatty acids obtained from a fish oil. Separation was attempted on three different types of column packing: cation exchanger impregnated with silver nitrate, silica and anion exchanger treated with potassium permanganate. Separation on the argentation column resulted in relatively good resolution of geometric isomers of dienes and trienes. Further, this column performed well in the separation of fatty acid methyl esters from a fish oil. Separatiaon of the same sample on a column packed with silica was somewhat less complete. Finally, a permanganate-treated anion exchanger separated the fatty acid methyl esters into groups according to the degree of unsaturation.

Characterization of fuels by multi-dimensional supercritical fluid chromatography and supercritical fluid chromatography-mass spectrometry

Abstract A multi-dimensional supercritical fluid chromatographic (SFC) system was evaluated for the determination of saturated compounds, alkenes, mono-, di- and triaromatics and polar compounds in diesel fuel distillates. The system consisted of three packed microcolumns, which were packed with cyano-modified silica, silica and in situ silver ion-impregnated cation exchanger. Further, an interface for SFC—electron impact MS was constructed. The application of direct fluid introduction was possible when packed microcolumns of 50 μm I.D. were employed. The different groups of organic compounds were readily separated, with the exception of alkanes/alkenes and monoaromatics. This separation became increasingly incomplete as the boiling range of the distillates was increased. Using SFC-MS, it was found that the lack of baseline separation depended solely on the tailing of the alkane/alkene peak. However, for most diesel distillates, only a minor part of the alkane/alkene peak co-eluted with the monoaromatics. In addition, examination by SFC-MS provided data for the proper selection of integration limits. The determination of aromatics was in good agreement with the results obtained using the HPLC method IP 391/90.

Quantitative hydrocarbon group analysis of gasoline and diesel fuel by supercritical fluid chromatography

A two-dimensional supercritical fluid chromatographic system is described for the determination of saturates, alkenes and mono-, di- and tri-aromatics in gasoline and diesel fuel. Aromatics were isolated from saturates/alkenes and group separated according to the number of aromatic rings on a capillary column packed with silica of particle size 4 μm. The alkenes were separated from saturates on a 38-mm capillary column packed with a silica-based cation exchanger which had been modified in situ with silver nitrate. Elution of alkenes was facilitated by the use of a relatively high column temperature, 65°C, and operation in the back-flush mode. Carbon dioxide was used as the mobile phase. Relative standard deviations were generally in the range 0.4–20.0%. At a low content of alkenes, 0.5%, a relative standard deviation of 8.4% was achieved. The analysis time was under 8 min. The utility of the method is demonstrated by the analysis of feedstock before and after hydration.

Semi-continuous extraction/purification of lipids by means of supercritical fluids

Abstract A method for semi-continuous extraction using supercritical carbon dioxide has been developed. In this technique, two streams, a solution of the material that will be fractionated and supercritical carbon dioxide, are coaxially introduced to a nozzle where a spray is formed. Extensive physical contact between the supercritical fluid and the feed solution is achieved in the spray thus facilitating extraction. The performance of the extractor is illustrated by the extraction of triacylglycerols (TGs) from an acetone extract of oat bran. In the extractor, the TGs are dissolved in the CO2 and removed from the precipitation unit with the stream of CO2. The target product, which is digalactosyldiacylglycerol (DGDG) is trapped in the precipitation unit. Through-put is related to the desired purity of the product. A DGDG purity of 95.4% was obtained at a solvent/feed ratio (S/F) of 48, the rate of production was then about 1 g/h. At a S/F of 200 the purity of the DGDG was 97%.

Characterization of triacylglycerols in the seeds ofAquilegia vulgaris by chromatographic and mass spectrometric methods

A combination of analytical techniques is generally necessary to properly characterize complex lipid materials. Chromatographic separation in conjunction with spectroscopic characterization was utilized for the analysis of the triacylglycerols in the seeds ofAquilegia vulgaris. Reversed-phase high-performance liquid chromatography (HPLC), micropacked argentation supercritical fluid chromatography (SFC), and combinations of the two techniques were used. The fatty acid profile was determined by gas chromatography/mass spectrometry of the picolinyl esters and by gas chromatography/flame-ionization detection of the methyl esters. The major components were also identified by direct inlet mass spectrometry. The excellent selectivity of packed fused silica argentation SFC for the separation of triacylglycerols was demonstrated.

Supercritical fluid chromatography: Open tubular vs. packed columns

Abstract This review covers the performance of open tubular and packed columns in SFC. Issues such as column dimensions, stationary phases, pressure drop, mobile phase gradients, injection and detection are considered. Further, the role of SFC in chromatography is discussed. Generally, open tubular columns are preferred for separations of complex mixtures, isomers and for eluting polar solutes with neat carbon dioxide. With current techniques high plate counts can be obtained, but analysis times are then relatively long. Although packed columns can give quite rapid separations, due to the pressure drop restriction, high plate numbers cannot be achieved. Universal detection is possible, also when polar mobile phase modifiers are used, with e.g. the evaporative light scattering detector and the mass spectrometer. The advantages of mobile phase composition programming are demonstrated.

Permanganate-impregnated packed capillary columns for group separation of triacylglycerols using supercritical media as mobile phases

Abstract Capillary columns packed with a silica-based anion exchanger were treated in situ with a solution of potassium permanganate. These columns showed highly reproducible retention times when used under supercritical conditions. Column temperatures up to 140°C could be applied. This type of column was successfully used for the group separation of triacylglycerols from vegetable oils according to their degree of unsaturation.

Modifications of poly(methyl-3-propylthiol)siloxane to give stationary phases for open tubular supercritical fluid chromatography

SummaryPoly(methyl-3-propylthiol)siloxane has been evaluated for use as stationary phase in open tubular columns for gas and supercritical fluid chromatography. Immobilization of the stationary phase was achieved by crosslinking with 2,4,6-trichloro-1,3,5-triazine. The poly(methyl-3-propylthiol)siloxane stationary phase film was in situ oxidized to the disulphide and sulphonic acid forms and both have been evaluated for use in supercritical fluid chromatography. Good selectivity towards polar polycyclic aromatic compounds has been shown. All the modified forms of the stationary phase were loaded with silver ions and were evaluated with regard to ligand exchange chromatography using supercritical fluid carbon dioxide as a mobile phase. The utility of the stationary phase, having sulphonic acid groups loaded with silver ions, has been demonstrated by separation of fatty acid methyl esters according to their unsaturation.