Thin-layer chromatography distribution

Lipid Screening. The problems of lipid analysis in the newborn is difficult because of the fact that most methods for analysis for lipids require substantial amounts of serum, yet a total lipid determination is very important in various types of disease. This problem can be solved by thin-layer chromatography (59). Figure 38 shows a typical pattern obtained when an extract 7rom 10 microliters of serum is subjected to thin-layer chromatography. If these specimens are scanned, and an internal standard is run, one can obtain a rough approximation of the distribution of the various lipids in the serum. This is shown in Figure 39, in which a normal specimen is run in an adult. 

FIGURE 12.3 Particle sizes and particle size distribution of silica stationary phases for planar chromatography. (From Nyiredy, S., Preparative layer chromatography, in Handbook of Thin Layer Chromatography, 3rd ed., Vol. 89, Sherma, J. and Fried, B., lids., Marcel Dekker, New York, 2003, pp. 99-133. With permission.)... 

Lipophilicity represents the affinity of a molecule or a moiety for a lipophilic environment. It is commonly measured by its distribution behavior in a biphasic system, either liquid-liquid (e.g. partition coefficient in 1-octanol-water) or solid-liquid (retention on reversed-phase high-performance liquid chromatography or thin-layer chromatography system). 

The theoretical work that exploited the advantages of the multidimensional separation format appears to have been developed much later than the original experimental work. One of the earliest studies was conducted by Connors (1974), who assumed that the distribution of spots on a two-dimensional thin-layer chromatography (2DTLC) plate could be modeled using a Poisson distribution of data on each retention axis. He then constructed equations that related the number of chromatographic systems needed to resolve a specific number of compounds. One... 

The logarithm of the 1 -octanol - water partition coefficient, denoted log Kq j or log P, indicates the distribution of the compound between the organic and the water phase. For highly lipophilic compounds, the log P is determined via reversed-phase thin-layer chromatography, giving the so-called log P tlc value1. 

Molyneux, R.J., James, L.F., Panter, K.E. and Ralphs, M.H. (1991b). Analysis and distribution of swainsonine and related polyhydroxyindolizidine alkaloids by thin layer chromatography, Phytochem. Anal., 2, 125-129. 

The only method that can be used routinely to identify organoas-tatine compounds is measurement of radioactivity based upon its distribution over two or more phases. Such techniques are gas-liquid chromatography (GLC), high-pressure liquid chromatography (HPLC), thin-layer chromatography (TLC), and electrophoresis. 

Thin-layer chromatography (75) and sodium dodecylsulfate-(poly)acrylamide gel electrophoresis (SDS-PAGE) are helpful for analyses of the lipid and protein composition, respectively. Size-exclusion chromatography allows estimation of the size distribution of the (proteo)liposomes and crude fractionation of the material as reviewed in Ref. 76. Accurate determinations of size distributions require analyses by static or dynamic... 

Amino acids have high melting or decomposition points and are best examined for purity by paper or thin layer chromatography. The spots are developed with ninhydrin (see Lederer and Lederer, p.44). Customary methods for the purification of small quantities of amino acids obtained from natural sources (i.e. l-5g) are ion-exchange chromatography (see p. 20) or countercurrent distribution (see p. 28). For general treatment of amino acids see Greenstein and Winitz [The Amino Acids, Vols 1-3, J.Wiley Sons, New York 1961]. 

Thin-layer chromatography (TLC) is a common laboratory technique for separating complex mixtures of solutes, usually by an adsorbtion mechanism. Several laboratories have applied the technique to the separation of polymer fractions and characterization of polymer molecular weight distributions. This work reviews the experimental results and theoretical approaches to the fractionation mechanisms. 

Because of the similarities in the theory and practice of these two procedures, they will be considered together. Both are examples of partition chromatography. In paper chromatography, the cellulose support is extensively hydrated, so distribution of the solutes occurs between the immobilized water (stationary phase) and the mobile developing solvent. The initial stationary liquid phase in thin-layer chromatography (TLC) is the solvent used to prepare the thin layer of adsorbent. However, as developing solvent molecules move through the stationary phase, polar solvent molecules may bind to the immobilized support and become the stationary phase. 

The scope of this review is limited to the hop-borne a- and /3-acids and to products derived from them that have appreciable commercial relevance. Thus, the liquid chromatography of the iso-a-acids and their chemically modified counterparts as well as of the hulupones will be considered. By far the major focus here will be HPLC analyses, but other methodologies that have been applied (countercurrent distribution, gas chromatography, supercritical-fluid chromatography, thin-layer chromatography, and micellar electrokinetic chromatography) will also be briefly considered. 

Chromatography is a separation process which depends on the differential distributions of the components of a mixture between a mobile bulk phase and an essentially thin film stationary phase.53-56 The stationary phase may be either in the form of a packed column (column chromatography) through which a mobile phase is allowed to flow, or in the form of a thin layer adhering to a suitable form of backing material (thin-layer chromatography) over which the mobile phase is allowed to ascend by capillary action. 

The enzyme DGAT has not been purified to date, probably because it is a hydrophobic and integral membrane protein. Therefore, DGAT activity was measured using rat liver microsomes as an enzyme source and radiolabeled palmitate as a substrate by the method of Mayorek and Bar-Tana [52] with some modifications [53], The reaction mixture contains microsomal protein, BSA, [14C]palmi-toyl-CoA, MgCl2, diisopropyl fluorophosphate, 1,2-dioleoyl-vw-glyccrol, and a test sample in a total volume of 0.2 ml. After a 15-min incubation at 23°C, lipids are extracted and separated by thin-layer chromatography (TLC). The distribution of radioactivity on TLC is analyzed with a radioscanner to determine the amount of [14C]TG. 

Distribution of Pesticides in Human Organs as Determined by Quantitative Thin-Layer Chromatography... 

Fig. 4.5. Sphingomyelin synthesis in Hymenolepis diminuta distribution of label in various intermediates, separated by thin-layer chromatography, after incubation with cytidine-5 -diphospho [methyl-13C]choline. The position of the lipid standards is indicated by the arrows, (a) sphingomyelin (b) dihydrosphingosine (c) sphingosine (d) ketosphingosine (e) ceramide. The origin is at band O. d.p.m., disintegrations/min. (After Bankov Barrett, 1985.)...

Methyl Esters. These long-chain acyl esters are subjected to thin-layer chromatography, colorimetric analysis, and gas-liquid chromatography, coupled with mass spectrometry, as described in Chapter 4. These assays will provide information on the ester/P molar ratio (based on starting phosphate value it should be 2.0) and on the composition and relative distribution of fatty acyl residues. 

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