Chromatography main components

Tar. Before the development of gas chromatography (gc) and high pressure Hquid chromatography (hplc), the quantitative analyses of tar distillate oils involved tedious high efficiency fractionation and refractionation, followed by identification or estimation of individual components by ir or uv spectroscopy. In the 1990s, the main components of the distillate fractions of coal tars are deterrnined by gc and hplc (54). The analytical procedures included in the specifications for tar bulk products are given in the relevant Standardi2ation of Tar Products Tests Committee (STPTC) (33), ISO (55), and ASTM (35) standards. 

Gel permeation chromatography studies using both refractive index and UV(260 nm) absorption detections have confirmed that both Acacia Senegal and Acacia seyal gums consist of three main components (Islam et al., 1997, Idris et al., 1998, Williams Phillips, 2000, Al Assaf 2006) ... 

The thermal cracking of a light ffaction of mixed plastics waste was carried out in a fluidised bed reactor and the fractions obtained were analysed by elemental analysis, gas chromatography and ashing. The main components of the waste were PE and PP with a small amount of PS and the bed was fluidised by pyrolysis gas, nitrogen or preheated steam. Experiments conducted at different temperatures and residence times were compared by calculating the crack severity for each experiment. The results obtained revealed that the amounts of ethene and propene obtained by pyrolysis with steam were comparable with those obtained using a commercial steam cracker. 

The main components of each fraction were purified by a combination of gel permeation and anionic interchange chromatography and their structure partially elucidated. 

In reversed-phase thin-layer chromatography (RP-TLC), the choice of solvents for the mobile phase is carried out in a reversed order of strength, comparing with the classical TLC, which determines a reversed order of values of compounds. The reversed order of separation assumes that water is the main component of the mobile phase. Aqueous mixmres of some organic solvents (diethyl ether, methanol, acetone, acetonitrile, dioxane, i-propanol, etc.) are used with good results. 

Figure 7.26 Structure, name and abundance of the main components of Irgafos P-EPQ, according to the manufacturer (Ciba-Geigy Ltd). After Bruheim el al. [511]. From I. Bruheim et al., Journal of High Resolution Chromatography, 23, 525 -530 (2000). Wiley-VCH, 2000. Reproduced by permission of Wiley-VCH...

From a practical point of view, and related to method development for impurity testing, it can be recommended that a method be developed in such a way that the impurity elutes before the main component. It will be easier to obtain a baseline separation and one that reduces quantification problems that might occur when the impurity elutes in the tail of the main peak. Moreover, the peak obtained for the main compound might be rather broad and tailing in chiral chromatography (as will be shown further in this chapter) which favors even more the development of methods with the impurity eluting first. 

During the last decade capillary electrophoresis (CE) has become a mature separation technique for pharmaceutical analysis. Numerous validated methods from pharmaceutical R D lahoratories and academia have been reported in literature, including identity confirmation, main component assay, purity determination, enantiomeric separation, and stoichiometry determination. In addition, CE is frequently applied as an orthogonal technique during the development of stability indicating liquid chromatography methods. As a result CE... 

The reaction of nitroethane/sodium ethoxide with the dialdehyde (31), obtained by periodate oxidation of methyl a-L-rhamnopyranoside (30), leads after deionization to a sirupy mixture (32), which was shown by thin-layer chromatography to contain five main components together with traces of other substances. After acetylation one di-O-acetate (33) crystallized from the mixture and was isolated in 12.5% 5deld, based on the rhamnoside (30). Reduction ot (33) with lithium aluminiumhydride gave methyl 3-C-methyl-3-amino-3,6-dideoxy-a-L-glucopyranoside (34), which was additionally characterized as the triacetate (35)... 

Exhaustive chlorination of thianthrene yields a mixture of polychloro-derivatives, the main component being 2,3,7,8-tetrachlorothianthrene (77USP3989715). In a survey, authors looking for dioxinlike activity in sediment from a sanitary sewer near a chemical factory detected tetrachlo-rothianthrene using gas-liquid chromatography and mass spectrometry (85MI4). 

Colistin is a linear-ring peptide antibiotic. Its main components are colistin A and colistin B. It is a member of the polymyxin family of antibiotics that is stable in dry form and in water solution. The sulfate salt of colistin, which is usually administered as feed additive, is soluble in water, slightly soluble in methanol, and practically insoluble in acetone and ether. Colistin components do not have any specific fluorophore and UV chromophore, so detection by liquid chromatography at residue levels of interest is difficult without including a suitable derivatization step in the analytical method. 

The volatiles of fresh leaves, buds, flowers and fruits were isolated by solvent extraction and analysed by capillary gas chromatography-mass spectrometry. Their odour quality was characterized by gas chromatography-olfactometry—mass spectrometry (HRGC-O-MS) and aroma extract dilution analysis (AEDA). In fresh bay leaves, 1,8-cineole was the major component, together with a-terpinyl acetate, sabinene, a-pinene, P-pinene, P-elemene, a-terpineol, linalool and eugenol. Besides 1,8-cineole and the pinenes, the main components in the flowers were a-eudesmol, P-elemene and P-caryophyllene, in the fruits (EJ-P-ocimene and biclyclogermacrene, and... 

Does the order of retention of the main components of the essential oils correlate with the structural differences in the main components For instance, anethole (main component in anise oil) is retained longer than is eugenol (main component in clove oil) explain this in terms of reverse-phase chromatography. If you cannot explain why the retention is as it occurs, refer to Chapter 4 and 5 or to the results of Chapter 12 (Experiment 5 Reverse-Phase Chromatography) for suggestions. 

Cholesterol is one of the main components of cell membranes and has several functions in the body, including the synthesis of certain hormones such as vitamin D and bile acid. Over the years, gas chromatography has been used to characterize cholesterol and its derivatives. Thiam et al. [123] developed an isocratic CEC method that allows baseline separation of a complex mixture of cholesterol and 12 ester derivatives in less than 40 min. The use of a polymeric surfactant, poly(sodium N-undecanoyl-L-glycinate), in the CEC buffer reduced migration time and improved resolution of the analytes. 

Acetylation of the mixture of products from the oxo reaction on the 3-acetate of (65) afforded a mixture of compounds that was shown, by gas — liquid chromatography, to consist of three main components in about 90% yield. Further work is in progress on the determination of the structure of the remaining components. 

Several approaches were taken. Capillary-column gas chromatography on a vinylation reaction product showed 24 separate peaks present in the hexenyl acetate fraction however, six of the peaks accounted for about 90% of the total sample. Hydrogenation of the reaction mixture (hydrogen over platinum on carbon) reduced the hexenyl acetates to a mixture of three hexyl acetates and thereby greatly simplified determining the position of oxygen substitution with, however, loss of information on olefin position. We tried to synthesize the specific hexenyl acetate isomers by the ester interchange reactions (Reactions 7a, 7b, and 7c). Mixtures of isomers were obtained, but they corresponded to the main components of the vinylation reaction mixture. For example, the main products isolated from the vinylation of hexene-1 corresponded to the products from Reactions 7a and 7b—i.c., vinyl rather than allyl esters. 

Fig. 1 Schematic representation of a mass spectrometer depicting its main components and the different modes used. Abbreviations DIP direct insertion probe DEP direct exposure probe GC gas chromatography LC liquid chromatography CE capillary chromatography TEC thin-layer chromatography FEE field-flow fractionation APCI atmospheric pressure ionization El electron impact Cl chemical ionization FAB fast-atom bombardment PD plasma desorption MALDI matrix-assisted laser desorption ionization ED laser desorption TSP thermospray ESI electron spray ionization HSI hypherthermal surface ionization Q quadropole QQQ triple quadropole TOE time-of-fiight FTMS Fourier transform mass spectrometer IT ion trap EM electrom multiplier PM photomultiplier ICR ion cyclotron resonance.

Starting with the description of the main components of a chromatographic unit, Chapter 5 gives an overview of process concepts available for preparative chromatography. 

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