Precipitation fractionation

The clear serum of this example is an amber liquid free from prothrombin, thrombin, fibrinogen and fibrin. It contains profibrinolysin and is excellently suited to further purification by salt precipitation fractionation, as given below. 

Also, the figures contain nephelometric curves for the product t (that is, for p + s, in the proportions formed in the synthesis) and the fraction o, which was also a thermally precipitating product and deposited onto the walls of the reaction vessel in the course of the copolymerization of NVC1 with NVIAz at their initial molar ratio of 85 15 (Table 1). One can see that the precipitation behaviour of the total product t differs, although the amount of the s-fraction is almost the same at 31-33%. Obviously, this depends on the properties of the s-fraction. For instance, the heat-induced precipitation of the sample t formed from the feed with a comonomer molar ratio of 90 10 (Fig. 3b) is suppressed by the presence of its own s-fraction to a markedly lesser extent when compared to the product t obtained at the comonomer molar ratio of 85 15 (Fig. 3a). Most likely, such differences reflect the divergent influence of the s-fractions on the coagulation processes in the thermo-precipitating fractions of the total product t. These differences, for example different surface... 

Table 2 Molecular parameters of the thermally precipitating and non-precipitating fractions of poly(NVCl-co-NVIAz) in aqueous solutions at 20 and 50 °C (the data from [42])... 

Figure 1. Compositional distribution of a predominantly syndiotactic copolymer bearing COCHiSOsN(CHs)t units (DPn = 650, DSm = O 366) from precipitation fractionation data. System 1 (6) CHCls—Et2C) system II (O) DMF—Hs0 + O, 5% NH4Cl cross fractionation ( ) intermediate fractions obtained from system II are further fractionated according to System I.

The fractions coilected are each run dropwise into 100 ml of stirred methanol to which two drops of concentrated hydrochloric acid have been added.Turbidity or precipitation will be observed from about the 6th fraction to about the 20th fraction.The precipitated fractions are filtered off, washed with methanol and dried to constant weight in vacuum at 20 °C. For each fraction the viscosity is measured in water at 25 °C using a capillary viscometer (capillary diameter 0.35 mm) and at as high a concentration as possible (10 g/l) in order to minimize errors.The limiting viscosity number, and hence the molecular weight, is estimated (see Sect. 2.3.3.3.1). Adjacent fractions for which there may be insufficient material for a viscosity measurement,can be combined where necessary. 

The classical solvent precipitation fractionation technique provides reproducible fractionations for determining molecular weight distributions of CTPB and almost 100% recovery of the sample from the column. A solvent-nonsolvent combination which has been used effectively is the toluene—acetone-methanol system, where acetone and methanol are used as the nonsolvents. The precipitating fractions are required to stand approximately 24 hours to ensure complete separation. Each fraction is vacuum stripped of solvent at approximately 30 °C., and the molecular weight of each fraction is then determined by either VPO or intrinsic viscosity. 

Figure 18. Reproducibility of the solvent precipitation fractionation technique for determining molecular weight distribution (molecular weights by intrinsic viscosity)...

Reactive extraction of lignin from red spruce has been studied using supercritical methylamine and methyla-mine-nitrous oxide binary mixtures. The wood residues and precipitated fractions after extractions have been characterized by chemical and spectroscopic procedures. 

The cis and trans isomers may be separated by fractional precipitation, fractional crystallization, or careful fractional distillation. 

A salt-precipitated fraction of ribonuclease contained two contaminating protein bands in addition to the ribonuclease. Further studies showed that one contaminant had a molecular weight of about 13,000... 

The critical surface tensions of the doubly precipitated fractions versus conversion are shown in Figure 16. Here we note an abrupt rise in yc and then a plateau band between 34 and 35.5 dyne/cm. These increases in yc, though higher than expected, could be caused predominantly by the grafting of styrene to the rubber as observed in normal random copolymerization (37, 38). 

Fig. 13. Schematic representation of successive precipitation fractionation (SPF) and successive solution fractionation (SSF)38)...

Strong interaction of volatile aldehydes occur naturally in soy protein products (9). Arai et al. (10) found that 1-hexanal is one of the major odorants of soybean and that this aldehyde interacts readily with soy protein. In order to determine whether the interaction is enhanced by denaturation of protein, Arai et al. (9) did three experiments under different conditions. In the first experiment (I), an acid-precipitated fraction of... 

The classical approach is based on the dependence of copolymer solubility on composition and chain length. A solvent/nonsolvent combination fractionating solely by molar mass would be appropriate for the evaluation of MMD, another one separating with respect to chemical composition would be suited for determining CCD or FTD. However, in reality, precipitation fractionation yields fractions which vary both in chemical composition and molar mass. Even high resolution fractionation would not improve the result. Narrower fractions can be obtained by cross-fractionation separating in two different directions. However, even in this case, it is almost impossible to obtain perfectly homogeneous fractions. 

Figure 1, a modification of the method used by Puski and Melnychyn (JO, shows the preparative procedure used to isolate an acid-precipitated fraction of soymilk protein (RDP). 

The functionality distribution of HTPB 134> can be obtained using the double detection procedure after derivatization of the OH groups with phenyl isocyanate. However, a true fractionation can been obtained by stepwise elution from silica gel n8,120) and, coupled with GPC, it enables establishment of the relationship between functionality and molecular weight distributions. Precipitation fractionation can also be used... 

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