Methods of Fractionation

A number of patents on the fractionation of starch concern the industrial production of starch fractions. Although most of them have not been applied in actual practice (and, therefore, no adequate evaluation of their results is possible), it is of some interest to give a short description of their details. 

This situation does not apply to the method of fractionation based on the use of aqueous salt solutions, as this process has been in actual operation for several years and the resulting products are commercially avail-able consequently, a more detailed description of this process is possible. The experimental results and the fundamentals of the mechanisms involved in the salt method have been treated at length in Section IV its technological features will now be mentioned briefly. 

The presence of relatively high concentrations of alcohol in the fractionating media has the additional advantage that defatting of the com starch, prior to its fractionation, is unnecessary. It is clear that this process lends itself to continuous operation in a closed cycle, as the aqueous alcohol can, after removal of the amylopectin fraction, be used for dissolving and processing fresh portions of starch. 

In order to effect complete dissolution of starch at temperatures below 100°, Bauer and Pacsu recommended the use either of dilute alkali or of dilute acid solutions. Accoixling to their so-called alkali process, defatted corn starch is dissolved in 0.5 to 1.0 N alkali at room temperature. Sufficient mineral acid is added to the resulting solution to bring its pH within the limits of 10-4. After saturation with (for example) Pentasol (a mixture of primary amyl alcohols), the system is heated for several minutes at a temperature between 60° and 100° on cooling, an amylose precipitate is obtained which can readily be separated in an ordinary, industrial centrifuge. Addition of excess methanol to the supernatant liquor causes precipitation of the amylopectin. Different kinds of starches can be fractionated by this method. Starch concentrations of up to 5% are claimed to give about a 24% yield of amylose (showing an iodine value of 16.0%) and a 76% yield of amylopectin (with a 0.9% iodine absorption). 

If dilute acids are employed as fractionating media, far higher starch concentrations can be handled. Starch concentrations of up to 20% 

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Physical methods of fractionation of tar sand bitumen usually indicate high proportions of nonvolatile asphaltenes and resins, even in amounts up to 50% wt/wt (or higher) of the bitumen. In addition, the presence of ash-forming metallic constituents, including such organometaUic compounds as those of vanadium and nickel, is also a distinguishing feature of bitumen. 

Another method of fractional crystallization, in which advantage is taken of different ciystallization rates, is sometimes used. Thus, a solution saturated with borax and potassium chloride will, in the absence of borax seed ciystals, precipitate only potassium chloride on rapid coohng. The borax remains behind as a supersaturated solution, and the potassium chloride crystals can be removed before the slower borax crystalhzation starts. 

LMWHs are formed by various methods of fractionation or depolymerization of polymeric heparin (Table 7.1). Although they are enzymatically derived from UFH, they have a different site of achon and can be administered subcutaneously. LMWHs exert their anhcoagulant effect by inhibiting factor Xa and augmenting tissue-factor-pathway inhibitor, but minimally affect thrombin or factor Ila (Figs. 7.1 and 7.2)." Thus, the PTT, a measure of antithrombin (anh-factor Ila) achvity, is not used to measure the achvity of LMWHs. 

Of course these classes do not constitute a single protein but mixtures of proteins having the same solubility characteristics. Improved methods of fractionation reveal how many different components are present in each fractionation. 

ABN separation a method of fractionation by which petroleum is separated into acidic, basic, and nentral constitnents. 

The program listing below represents an interactive program written in turbo PASCAL to simulate a cyclic voltammogram. The iterative procedure employs the method of fractional steps. ... 

Meanwhile, the described methods of fractionation came into general synthetic practice. For instance, mesitaldehyde-3,5-d2 was prepared by reaction of mesitaldehyde with D2SO4 following up to the arene protio-deuterio exchange method (Jiao et al. 2007). 

An alternative method of fraction (see Fig. 2) has been developed which takes advantage of the observation that cleavage of the single disulfide bond induces the dimer - monomer transition of fraction IV (B6, S17, S19). If the fractionation procedure is carried out in the presence of a reducing agent, such as j8-mercapthoethanol, the reduced IV can be reoxidized into the dimer form by oxygen. The choice of the method... 

The fluorimetric determination of corticosteroids in sulfuric acid-ethanol mixtures has given rise to numerous studies, particularly with the aim of estimating these compounds in urine or plasma. These all require prior methods of fractionation to permit a more or less selective separation of the various corticosteroids. The purified sample solution is then evaporated to dryness, and the residue treated with the reagent to yield fluorescence which can be measured [72]. 

The development of adsorption as a method of fractionation has been analogous to the development of distillation. In both cases the operation was originally carried out in a simple batch unit. After many years, rectification was added and close fractionation became possible. In the case of distillation this was done by adding a packed or bubble plate column to the still kettle. In the case of adsorption it involved the use of an adsorbent-packed column to obtain chromatographic separation, which gave a rectification effect. 

Long ago it has been established that nitrocellulose is not a homogeneous substance. The earliest experiments in this field were made by Stepanov [100] who used the method of fractional precipitation from an acetone solution by the addition of water. Stepanov added different amounts of water stepwise to a solution of nitrocellulose in acetone to obtain fractions varying slightly, corresponding with the nitrogen content. The first and least soluble fraction contained 13.15% of nitrogen, while the N-content of the last, fifth portion, was 12.90%. 

In other experiments, the opposite method of fractionation by dissolution was applied. In this way G. Meissner [107] prepared a soluble fraction with a nitrogen content of 10.28%, in quantity about 4% by extracting a specimen of nitrocellulose with 12.17% N using 50 50 ether-alcohol. The insoluble part was composed of nitrocellulose of 12.32% N. 

In 1905 Hall and Smith 2 investigated all the then known methods for the removal of titanium, and tried various other processes they were unable, however, to improve on Marignac s method of fractional recrystallisation of the double potassium fluorides.3 This method has the disadvantage that in the case of the niobium salt protracted and tedious repetition is necessary before it is obtained free from titanium, and the method becomes impossible with small quantities of material.4... 

Ruff and Schiller 8 determined the solubilities of the double fluorides of niobium and tantalum, K2NbF7 and KaTaF7, in varying quantities of hydrofluoric add and potassium fluoride, and based a method of fractional separation on the results, which showed that the solubility of both fluorides diminishes with increasing concentration of potassium fluoride and decreasing concentration of hydrofluoric acid the solubility increases rapidly with rising temperature, and is always... 

Various procedures are used to separate milk proteins into fractions or individual components that can quantitated separately. A classic method of fractionation is by precipitation at pH 4.6, which separates the proteins into two groups—caseins in the precipitate and whey proteins in the supernatant. All proteins are precipitated from a second aliquot with trichloroacetic acid at 12% (w/v) concentration (Rowland 1938), and concentrations of casein and whey proteins are calculated as follows ... 

Other methods of fractionation which utilize the presence of ionizable groups, either natural (such as carboxyl or amino groups), or induced (such as borate complexes), may be useful. Such methods have been discussed in reviews.248 2W Complexation (for example, with Fehling solution) was found useful in the study of a polymannose.216 An insoluble complex was formed, as with natural mannans. 

Gel-filtration is not especially effective for the purification of IgG, which tends to elute in a broad peak and is usually contaminated with albumin (mainly derived from dimeric albumin, Mr 135,000). The technique is more useful for the purification of IgM or may be used as an adjunct to ion-exchange chromatography. Some IgGs (monoclonal), however, possess pis that make them difficult to purify using ion-exchange chromatography. In such cases using gel filtration as a method of fractionation may be desirable (5). 

The methods of fractional liquefaction and distillation have very many similar and important applications in the chemistry of gases. 

The method of fractionation allows effective separation of the different components of the crude polymerizates the results are valid enough even if some limitations exist concerning the fraction eluted with di-methylformamide, which might dissolve grafted copolymers with a PVC content > 70%. 

The chemical composition of the heavier feedstocks is complex. Physical methods of fractionation usually indicate high proportions of asphaltenes and... 

There are many procedures that have received attention over the years (Speight, 1999 and references cited therein) but for the purposes of this text, this section will focus on the standard (ASTM) methods of fractionation. 

Other methods of fractionation with supercritical fluids are conceivable. One such possiblility could involve manipulation of the pressure during the destraction or upon subsequent separation of the fluid and residuum. The relative merits of such possibilities remain to be explored. Successful development of such technology will result in the ability to fractionate and characterize material currently intractable by conventional methods. 

The radiochemical procedures required skill and delicacy but they were not conceptually new. To verify the presence of radium, Hahn and StraKmann tried to separate it from its barium carrier, using Marie Curie s method of fractional... 

The methods of fractionation listed in Lewkowitsch (1904) soon led to the separation and determination of individual fatty acids in fats. These were listed in Hilditch and Williams (1964) and the values obtained for major components were usually very similar to those later determined by GC. 

A proper method of fractionation is indispensable in the study of the composition of coal-derived liquids (CDL). Data in Table II show large differences between solvent extraction and distillation as fractionation methods. Two fractions, ES and EI-AS, from ethanol extraction exhibited little differences from each other, while two fractions from distillation of ES revealed marked differences in molecular weight, H/C ratio, hydroxyl group content and physical appearance. 

Infrared data on all fractions of Polymer XX (Table X) collected by both methods of fractionation revealed no discernible differences by comparison of any two fractions. 

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