Fractionation methods chromatographic

Although the traditional method of separating the diastereomeric compounds generated in a resolution procedure is fractional crystallization, chromatographic procedures are now common and convenient. Diastereomeric compounds exhibit different adsorption... 

Separation methods The methodology for their separation often consists of fractionation methods (see Section 3.3.4) and chromatographic methods of the soluble species. Common detection methods are AAS, ICP-OES, and fluoride electrode methods. 

The fractions from elution chromatography were studied by a number of spectroscopic methods, n.m.r., i.r., u.v., fluorescence and phosphorescence spectroscopy. Equivalent fractions from chromatographic separation of the various oils showed no significant differences in their spectra and it appears that the composition of the fractions was independent of the catalyst concentration used to produce the oil. Though, as previously mentioned the amounts of the various fractions especially the polar fractions differ with the catalyst concentration. G.1.C. analysis of the saturate fractions also indicated no changes with different catalyst concentrations. 

In this chapter, we restrict our discussion to a chromatographic technique normally used for molecular weight measurements. The chromatographic concept can also be used for direct size (instead of molecular weights) measurement in the case of rigid particles, as we illustrate in our description of field-flow fractionation methods in Chapter 2. 

Methods of Analysis. Water Content of Fractions. A chromatographic method was employed using a glass column (6 ft x 0.2 mm ID) packed with Po-rapak QS. The chromatographs used were a Varian 3700 or a Hewlett Packard 5880. Water contents were also determined by the Karl Fisher method by Huffman Laboratories, Golden, Colorado. 

This book covers some of the significant advances in hyphenated chromatographic separation methods for polymer characterization. Chromatographic separation techniques in this volume include size-exclusion chromatography, liquid chromatography, and field flow fractionation methods that are used in conjunction with information-rich detectors such as molecular size-sensitive or compositional-sensitive detectors or coupled in cross-fractionation modes. 

E-3 Advantages of Field-Flow Fractionation over Chromatographic Methods... 

As a fractionation method, I developed chromatography of nucleic acids on hydroxyapatite, a calcium phosphate which had been used by Tiselius et al. (1956) for the fractionation of proteins. Previous observations (Bernardi and Cook, 1960a,b,c) that hydroxyapatite was particularly good as a chromatographic substrate for fractionating of phospholipoproteins characterized by different phosphorylation levels convinced me to try it on DNA. The main discovery was that hydroxyapatite could fractionate single- from double-stranded DNA (Fig. 1.4 left panel), the former being eluted by a lower phosphate... 

The approach adopted to obtain an exploitable pure plant constituent involves interdisciplinary work in botany, pharmacognosy, pharmacology, chemistry, toxicology. The plant material is extracted by solvents of increasing polarity, the extracts are screened with different bioassays and submitted to fractionation with chromatographic techniques. This process is repeated until the isolation of a pure active constituent which is finally identified by spectroscopic methods (bioactivity-guided isolation)(Fig. 1). 

Preparative GC offers the greatest resolving power of the fractionation methods. Traditionally, a flavor concentrate was chromatographed on a 0.125-inch or 0.25-inch o.d. packed column and the effluent collected via cold trap in numerous fractions. The solvent-free fractions could be subjected to sensory evaluation at this point to focus on a specific sensory property (e.g., an off-flavor or desirable note) or subjected to additional chromatographic separations. Today it is more common to use large... 

The most convenient way of separating phenols from the bulk of the material excreted in urine is steam distillation. Comparatively few compounds, however, are volatile in steam and a more general method which can be applied to almost all simple phenols is to extract the hydrolywd urine with ether in a continuous extractor for several hours. By adjusting the pH of the urine, it may be possible to separate phenols from phenolic acids a pH of 7.8 usually serves to prevent extraction of the acids while it permits extraction of other phenols. The phenolic acids can be subsequently extracted if the residual urine is adjusted to pH 1 (cf. Schmidt (80)). Tests may then be applied to the residue left after evaporation of the ether. If the phenols are liable to oxidation by atmospheric oxygen, e. g., aminophe-nols, the ether should be removed in vacuo or in a stream of nitrogen. The ether extract can be fractionated by conventional methods. Chromatographic separation of an ether extract on columns of powdered cellulose often provides a convenient method for the separation of mixtures of phenolic compounds (Section 11,4). 

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