Turbid solutions

Lipinski et al. [12] and Pan et al. [463] compared several commonly used methods of solubility measurement in early discovery, where samples are often introduced as 10 mM DMSO solutions. Turbidity-based and UV plate scanner-based detections systems were found to be useful. The methods most often used in discovery and in preformulation will be briefly summarized below. 

As is obvious from the Table 9.11, the concentration of Zn2+ ions in alkaline solution increased as the time of sonication increased. In particular, the increase in sonicated solutions was much more than in the unsonicated solution. Turbidity and conductivity of the solutions also increased gradually as time of sonication increased (Table 9.12). 

Retention of a protein or protein activity after 105,000y, 1 hr Chromatography on gel filtration columns with large pore sizes Electron microscopy—however, sample preparation may partially reconstitute membranes Decrease in solution turbidity, which may be detected by a diminution in light scattering or an enhancement in light transmission Diffusion of membrane lipids as assayed by nuclear magnetic resonance and electron spin resonance... 

Paar turbidimeter analychem Avisual-extinction device for measurement of solution turbidity the length of the column of liquid suspension is adjusted until the light filament can no longer be seen. par. tor-bo dim-ad-ar) paired electron phys chem One of two electrons that form a valence bond between two atoms. jperd i lek,tran ... 

PAAR TURBIDIMETER. A visual-extinction device for measurement of solution turbidity. The length of the column of liquid suspension is adjnsted until the light filament can no longer be seen. 

As it was shown, under AG polymerization ([AG] <1.3 mole-11) kinetic dependences of Vp on q % were linear, and polymerization solution remained completely transparent up to high conversions. At higher monomer concentration [AG] >1.5 mole-11 from the initial conversions the micro-heterogeneity is appeared. As far as the monomer is spent in reaction solution at high conversion degrees solution turbidity is gradually reduced and solution becomes absolutely transparent. 

Cellulose microcrystals can be suspended in dilute solution. Turbidity measurements suggest that the particles are not highly associated in the absence of added salt. In the presence of a low salt concentration, large aggregates are formed, as was shown by a study of light scattering by suspensions of ramie microcrystals 15). When the salt concentration is further increased, the microcrystals precipitate. Since the microcrystals... 

One factor which affects the extent of polymer-solvent interactions is relative molar mass of the solute. Therefore the point at which a molecule just ceases to be soluble varies with relative molar mass, which means that careful variation of the quality of the solvent can be used to fractionate a polymer into fairly narrow bands of polymer molar masses. Typically, to carry out fractionation, the quality of the solvent is reduced by adding non-solvent to a dilute solution of polymer until very slight turbidity develops. The precipitated phase is allowed to settle before removing the supernatant, after which a further small amount of non-solvent is added to the polymer solution. Turbidity develops once again, and again the precipitated phase is allowed to settle before removal of the supernatant. Using the technique polymers can be separated, albeit slowly, into fractions of fairly narrow relative molar mass. 

Ribereau-Gayon et al. (1976) emphasized that, in phosphatoferric casse, the wine does not become turbid due to clusters of ferric phosphate molecules, which are rather small and remain in the colloidal state in a clear solution. Turbidity, i.e. white casse, occurs when proteins, positively charged at the pH of wine, neutralize the negative charge of these phosphatoferric clusters, making them hydrophobic and therefore insoluble. Flocculation can only occur under these conditions. 

The test is described as the most sensitive of the contemporary colorimetric methods. The absorbance follows Beer s law and has a maximum at 635 nm. The position of the maximum varies, however, with the solvent used. The sulfamic acid, which is added to the reaction via the ferric chloride reagent, ensures that the colored compound does not precipitate, leaving the test solution turbid. This was often seen in older variants of the method, and... 

The effect of surfactants on the autooxidation of different thiols such as 2-mercaptoethanol (ME), 3-mercapto-1,2-propanediol (MPD), mercaptoacetic acid (MAAc) and dodecylmercaptan (DDM) in the presence of a polymeric catalyst, has been studied [155,156]. Fig. 20 illustrates the change in the initial rate of ME oxidation and the change in solution turbidity as a function of the concentration of the added anionic surfactant, sodium dodecylsulfate (DDS). The strong drop in the reaction rate and the increase in the turbidity of the system are apparently due to the formation of a complex between the polyion and the surfactant. However, the nonionic surfactant, oligoethylene oxide, does not influence ME oxidation. 

Other experiments. Precipitation of PPE from toluene with methanol yielded the same kind of agglomerates as with CO2. A major difference between the experiments was that only a few drops of methanol had to be added to turn the clear polymer solution turbid white, whereas when CO2 is used the liquid level first rises considerably. The way in which the solubility declines is therefore different for methanol and CO2. hi both cases the amount of crystalline material was approximately 25 %, and does not change significantly when methanol is used instead of CO2. 

For light scattering (bottom curve), the change in solution turbidity indicates the appearance of a scattering species of significantly greater size and optical properties than the monomeric solute. The effect on surface tension (middle curve) has already been introduced, but will be discussed in more detail below. These and many other types of measurement serve as evidence for the formation of aggregates or micelles in solutions of surfactants at relatively well-defined concentrations. 

Fig. 14. Graphical representations of increasing microsphere diameter with increasing cross-linker length and average diameters (top) before and after thermal annealing cycles (inset), and solution turbidity during annealing cycles (bottom).

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