Lipids chromatographic systems

A general chromatographic system for separation of lipids does not exist. Whereas sophisticated systems for groups of lipids are described in literature, do not hesitate to try other solvent systems. 

Determination of pesticide residues in fatty samples by GC requires the elimination of interfering compounds, mainly lipids, from the extracts before sample injection into the chromatographic system. Even small amounts of lipids can cause damage to the column and contaminate the detector. The effectiveness of HPLC techniques for the separation of different molecules makes this technique adequate for the cleanup of this type of samples. 

Selenomethionine forms optical enantiomers and a chiral column is needed to separate the two forms [160-162], As the presence of salts and organic matter can cause retention times to vary, it is essential that spiking is used to verify them. Also, it should be noted that retention time alone does not allow peaks to be unequivocally assigned. It has been found that the removal of lipid material prior to protein extraction dramatically improves the reproducibility of the chromatographic system and the lifetime of the columns. 

Some chromatographic systems have been designed in which untreated biological samples can be applied directly to the paper. The impure sample on the paper is chromatographed with hexane, which elutes the lipids with the solvent front. After drying, the paper is developed with pure water (if the analyte is water insoluble) to elute salts, sugars, etc. at the front. Finally, development with the proper mobile phase for the analytical separation is carried out, to a point below the purification developments. 

Kuksis A (1966) Quantitative lipid analyses by combined thin-layer and gas-liquid chromatographic systems. Chromatography Reviews 8 172-207. 

The great complexity of natural lipid mixtures normally necessitates the use of some form of chromatography for their separation. Since the nonpolar lipid molecules are often better resolved and recovered from chromatographic systems, the polar head group may be removed or masked with nonpolar groups prior to the chromatographic separation. 

For samples with a high lipid content (e.g., milk), additional cleanup of the extracts may be necessary to eliminate other lipids such as triacylglycerols. In the past, open-column chromatography on magnesia, alumina, or silica gel has been used. More recently, solid-phase extraction (SPE) on disposable prepacked cartridges filled with silica or Cig reversed-phase packing material has been applied to vitamin A analysis. SPE is a refinement of the earlier open-column chromatographic systems. 

The p-ELSD is thus an integrated part of our miniaturized chromatographic system for quantitative analysis of neutral as well as more polar lipids. 

The mobile phase consists of one or more solvents that are pumped through the chromatographic system, resulting in the separation of analytes. Mobile phases may also contain modifiers. Examples of frequently used solvents include hexane, methanol, 2-propanol, acetonitrile (ACN), and water. Examples of modifiers include tri-fluoroacetic acid, acetic acid, or formic acid. In general, the composition of the mobile phase should be kept simple. Factors that influence the choice of mobile phase include the solubility of the sample in the mobile phase, the polarity of the mobile phase, ultraviolet absorption wavelength, refractive index, and viscosity of the solvents. The purity of the solvents in the mobile phase is also important because the region of UV that is used for the detection of lipids (200-215 nm) must be free of interferences. For phospholipids, the most popular solvent systems are transparent to UV in the range of 200-215 nm they include... 

Quantitative Lipid Analysis by Combined Thin-Layer and Gas-Liquid Chromatographic Systems Chromatogr. Rev. 8 172-207 (1966) ... 

This section considers the various chromatographic systems, i.e., combinations of sample mixture, stationary phase, and mobile phase, used during TLC of lipids. Various types of development, i.e., one-dimensional (1-D), multiple development in the same direction, and two-dimensional (2-D), are considered here. 

Linear analyzers, 350-352.357 Linear development of TLC plate, 25-27 Lipids. 683-714 advantages of TLC. 683 chromatographic systems. 691-698 one-dimensional solvent systems, 692-b94 mobile phase, 692 stationary phases, 691-692... 

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