Isolation of ceramide fractions from skin sample by subcritical chromatography with packed silica and evaporative light scattering detection

Review of available "extraction + purification" methods of natural ceramides and their feasibility for sewage sludge analysis

Natural ceramide, a biologically active compound present in plants, has been used widely in food, cosmetics, and pharmaceutical industries. Abundant ceramide has been detected in sewage sludge, which has inspired the idea to recycle ceramide from it. Therefore, the methods of extracting, purifying, and detecting ceramides from plants were reviewed, with the aim to establish methods to get condensed ceramide from sludge. Ceramide extraction methods include traditional methods (maceration, reflux, and Soxhlet extraction) and green technologies (ultrasound-assisted, microwave-assisted, and supercritical fluid extraction). In the past two decades, more than 70% of the articles have used traditional methods. However, green extraction methods are gradually improved and showed high extraction efficiency with lower solvent consumed. The preferred technique for ceramide purification is chromatography. Common solvent systems include chloroform-methanol, n-hexane-ethyl acetate, petroleum ether-ethyl acetate, and petroleum ether-acetone. For structural determination of ceramide, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry are used in combination. Among quantitative analysis methods for ceramide, liquid chromatography-mass spectrometry was the most accurate. This review concludes that with our prilemenary experiment results it is feasible to apply the plant "extraction + purification" process of ceramide to sludge, but more optimization need to be performed to get better results.

UHPSFC/ESI-MS Analysis of Lipids

This new analytical approach for high-throughput and comprehensive lipidomic analysis of biological samples using ultrahigh-performance supercritical fluid chromatography (UHPSFC) with electrospray ionization-mass spectrometry (ESI-MS) is based on lipid class separation using 1.7 μm particle bridged ethylene hybrid silica columns and a gradient of methanol-water-ammonium acetate mixture as a modifier. The method enables a fast separation of 30 nonpolar and polar lipid classes within 6-min analysis time covering six main lipid categories including fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and prenols. Individual lipid species within lipid classes are identified based on positive- and negative-ion full scan and tandem mass spectra measured with high mass accuracy and high resolving power. The method is used for the quantitative analysis of lipid species in biological tissues using internal standards for each lipid class. This high-throughput, comprehensive, and accurate UHPSFC/ESI-MS method is suitable for the lipidomic analysis of large sample sets in clinical research.

Fast separation of triterpenoids by supercritical fluid chromatography/evaporative light scattering detector

The screening of plant material, the chemical composition, the abundance and the biological activity of triterpenoids are of a major economical importance. The classical analytical methods, such as TLC, GC, and HPLC are either little resolutive, or require derivatization steps, or fail in sensitivity. The supercritical fluid chromatography/evaporative light scattering detector (SFC/ELSD) coupling provides high resolution, fast analysis and higher responses for the analysis of triterpenoids. After the initial screening of seven stationary phases to select the well suited one, analytical conditions (modifier percentage, from 10 to 3%; backpressure (from 12 to 18 MPa) and temperature (from 15 to 25 °C) were studied to improve the separation, and ELSD detection of a standard mixture composed of 8 triterpenoids (oleanolic acid, erythrodiol, β-amyrin, ursolic acid, uvaol, betulinic acid, betulin, lupeol). Applied to apple pomace extracts, this method allows the separation of about 15 triterpenoid compounds, in less than 20 min, with isocratic conditions. Moreover, the ELSD response is dramatically higher than the one provided by UV detection, and avoids derivatization steps. An attempt to identify some compounds was done by collecting chromatographic peaks and further analyzing them with mass spectrometry. Complete identification or molecular formula could be proposed for 11 compounds. However, due to the presence of position and orientation isomers the absolute identification remains difficult, despite some retention rules deduced from the standard analysis.

Corona-Charged Aerosol Detection in Supercritical Fluid Chromatography for Pharmaceutical Analysis

In this paper we describe the coupling of a corona-charged aerosol detector (CAD) to packed column supercritical fluid chromatography (pSFC). The CAD can be coupled to pSFC by connecting the outlet of the back pressure regulator (BPR) directly to the inlet of the detector. To reduce the noise and increase the reproducibility, the transfer line (1 m x 0.25 mm i.d. stainless steel) was placed in a thermostatic bath at 45 degrees C. Limits of detection (LODs) ranged from 3 to 11.5 ng loaded on column, with an average value of 4.5 ng (from 0.6 to 2.3 mg/L, with an average value of 0.9 mg/L for 5 microL injection). To reduce differences in response at different mobile-phase compositions, mobile-phase flow compensation was performed by placing a T-piece before the BPR. In this way, the differences in response were significantly reduced from a factor of 2-3 to a factor of 1.2-1.7. Compared to CAD application without flow compensation, the average LOD was higher by a factor of approximately 1.8. However, the nearly uniform response in gradient analysis with mobile-phase flow compensation far outweighed the slight increase in the LOD. The performance of the pSFC-CAD combination was illustrated by the analysis of selected pharmaceutically related compounds. In addition, a comparison with UV detection was made. Measurement of analytes at a relative concentration of 0.05% versus the main component was demonstrated.

Characterisation of stationary phases in subcritical fluid chromatography with the solvation parameter model

In this third paper, varied types of polar stationary phases, namely silica gel (SI), cyano (CN)- and amino-propyl (NH2)-bonded silica, propanediol-bonded silica (DIOL), poly(ethylene glycol) (PEG) and poly(vinyl alcohol) (PVA), were investigated in subcritical fluid mobile phase. This study was performed to provide a greater knowledge of the properties of these phases in SFC, and to allow a more rapid and efficient choice of polar stationary phase in regard of the chemical nature of the solutes to be separated. The effect of the nature of the stationary phase on interactions between solute and stationary phases and between solute and carbon dioxide-modifier mobile phases was studied by the use of a linear solvation energy relationship (LSER), the solvation parameter model. The retention behaviour observed with sub/supercritical fluid with carbon dioxide-methanol is close to the one reported in normal-phase liquid chromatography with hexane. The hydrogen bond acidity and basicity, and the polarity/polarizability favour the solute retention when the molar volume of the solute reduces it. As with non-polar phases, the absence of water in the subcritical fluid allows the solute/stationary phase interactions to play a greater part in the retention behaviour. As expected, the DIOL phase and the bare silica display a similar behaviour towards acidic and basic solutes, when interactions with basic compounds are lower with the NH2 phase. On the CN phase, all interactions (hydrogen bonding, dipole-dipole and charge transfer) have a nearly equivalent weight on the retention. The polymeric phases, PEG and PVA, provide the most accurate models, possibly due to their better surface homogeneity.

Application of a xenon arc lamp as a light source for evaporative light scattering detection

The standard tungsten-halogen light source used in a commercial evaporative light scattering detector (ELSD) was replaced with a 180 W xenon arc lamp. The xenon arc lamp possesses a broader spectrum in the UV region than the halogen source. The influence of the UV transmittance of five selected solvents was studied with a size-exclusion chromatography column. This solvent parameter was not observed to influence the ELSD response between the two light source settings. With the solvents studied, better sensitivity was obtained with the xenon arc lamp than the halogen lamp. This high-energy source was applied to ceramide III analysis with an octadecyl-grafted silica column and methanol:tetrahydrofuran 97:3 as the mobile phase, and the sensitivity of the quantification of ceramide III increased 16-fold for injected amounts of 14 approximately 140 ng. The molecular species in a sample of naturally occurring ceramides was analyzed using two C18 columns at 40 degrees C and gradient elution from 100% acetonitrile to 100% isopropanol in 30 min. The increased ELSD sensitivity achieved when using the xenon arc lamp allowed both the minor and major ceramide species to be observed, in contrast to the results achieved when the halogen lamp was used, where the increased photomultiplier voltage needed to observed the signals from the minor species caused the signals from the major ceramide species to occur above the detector response window.

Microanalytical systems for separations of stratum corneum ceramides

The small amount of lipids from human skin obtained with noninvasive sampling method led us to investigate microanalytical separation techniques. The lipid class analysis was performed with a micro polyvinyl alcohol-silica (PVA-Sil) column. The gradient elution was from heptane to acetone/butanol 90:10 v/v in 4%/min at 78 microL/min. In addition an evaporative light scattering detector (ELSD) was modified for micro-LC. All solvents contained 0.1% of triethylamine and formic acid in stoichiometric amount, which increased the ELSD response. In these conditions, the cholesterol eluted before free fatty acid, and squalene and triglycerides close to the dead volume. The various ceramide classes eluted following the order of the increased number of hydroxyl groups. The LOD for ceramides was 2.2 ng. The advantages of this method are the use of a normal stationary phase more reliable due to its chemical stability, its surface homogeneity and its development in microchromatography without chlorinated solvents which offers small LOD and the whole profile of lipids present in stratum corneum (SC). A method using a narrow-bore PVA-Sil column was used to collect ceramide fraction. Then the molecular species were analysed with a porous graphitic carbon column in capillary LC using a gradient from CH3OH/CHCl3 70:30 v/v to CHCl3 at 2%/min with a flow rate at 5 microL/min. The LOD obtained for ceramide was 1 ng. Both methods were assessed with SC samples obtained by rinsing a 5.7 cm2 area of the forearm with 25 mL of ethanol.

Modelling of ceramide interactions with porous graphite carbon in non-aqueous liquid chromatography

Interactions of solutes on porous graphitic carbon (PGC) with non-aqueous mobile phases are studied by the linear solvation energy relationship (LSER). Studies have been carried out with eight binary mixtures composed of a weak solvent (acetonitrile or methanol) and a strong solvent (tetrahydrofuran, n-butanol, CH2Cl2, 1,1,2-trichloro-2,2,1-trifluoroethane). The systematic analysis of a set of test compounds was performed for each solvent mixture in isocratic mode (50:50). The results were compared to those obtained on PGC with hydro-organic liquids and supercritical fluids. They were then correlated with the observed retention behaviour of lipid compounds, more particularly ceramides.

Glycolipid class profiling by packed-column subcritical fluid chromatography

The potential of packed-column subcritical fluid chromatography (SubFC) for the separation of lipid classes has been assessed in this study. Three polar stationary phases were checked: silica, diol, and poly(vinyl alcohol). Carbon dioxide (CO2) with methanol as modifier was used as mobile phase and detection performed by evaporative light scattering detection. The influence of methanol content, temperature, and pressure on the chromatographic behavior of sphingolipids and glycolipids were investigated. A complete separation of lipid classes from a crude wheat lipid extract was achieved using a modifier gradient from 10 to 40% methanol in carbon dioxide. Solute selectivity was improved using coupled silica and diol columns in series. Because the variation of eluotropic strength depending on the fluid density changes, a normalized separation factor product (NSP) was used to select the nature, the number and the order of the columns to reach the optimum glycolipid separation.