Phosphates, colloidal

In principle, it would be logical to combine plots of the buffer index curves of each of the buffer components of milk and thus obtain a plot which could be compared with that actually found for milk. It is not difficult, of course, to conclude that the principal buffer components are phosphate, citrate, bicarbonate, and proteins, but quantitative assignment of the buffer capacity to these components proves to be rather difficult. This problem arises primarily from the presence of calcium and magnesium in the system. These alkaline earths are present as free ions as soluble, undissociated complexes with phosphates, citrate, and casein and as colloidal phosphates associated with casein. Thus precise definition of the ionic equilibria in milk becomes rather complicated. It is difficult to obtain ratios for the various physical states of some of the components, even in simple systems. Some concentrations must be calculated from the dissociation constants, whose... 

Calcium and magnesium influence the titration curves of milk because as the pH is raised they precipitate as colloidal phosphates, and as the pH is lowered, colloidal calcium and magnesium phosphates are solubilized. Since these changes in state are sluggish and the composition of the precipitates depends on the conditions (Boulet and Marier 1961), the slope of the titration curves and the position of the maximum buffering depend upon the speed of the titration. 

It is necessary to forewarm milk to impart adequate heat stability to the concentrate to permit it to withstand subsequent sterilization treatments. The heat-induced casein micelle-whey protein complexes in forewarmed milk are less sensitive to heat than native whey proteins and thus provide the required stability to the concentrate. The forewarming treatment also stabilizes the milk mineral system by com-plexing Ca and Mg ions with casein micelles and by converting ionic forms to the less reactive form of colloidal phosphate (Morr 1975). 

The colloidal phosphate, prepared by the action of concentrated ammonium hydroxide on ferric phosphate, has been studied by Holmes and Rmdfusz, J. Amer. Chem. Soc., 1916, 38, 1970. 

Phosphorus Bonemeal Colloidal phosphate Rock phosphate... 

In the next section, we shall discuss at some lei th the reversal of chaise of colloids of acidic nature with a greater number of inoi anic cations in neutral or slightly acid media, the ionogenic groups of all three kinds of colloids (phosphate, carboxyl, sulphate colloids) thus being practically wholly ionised. 

As a result of these tests, use of ground phosphate rock increased in the United States to a maximum of more than 1 million tpy in 1953. However, more recently use has decreased sharply, and in 1976 consumption amounted to only about 37,000 tonnes, including colloidal phosphate," a fine material recovered from Florida waste ponds. 

Colloidal phosphates of Ce, Hf, Sn, Ti adjusted to pH 9 with a volatile base. 

The actual surface structure is, of course, more complex than represented. A silica-based cation exchanger of this type could be used to separate metal ions such as Ag, Cu, Fe, Ca +, according to Kautsky and Wesslau (546). Ion-exchange surfaces of this type have been described by Yates (547), who prepared colloidal phosphates of Ti +, Zr +, Sn +, Hf, and Ce + and adsorbed them on the silica surface. The advantage of making an exchanger with a silica base rather than entirely of the polyvalent metal phosphate is that silica is easier to form into the wide-pored structure of high surface area needed for efficient performance. 

Richard Willstatter, who had already distinguished himself by elucidating the structure of chlorophyll, relied upon the same protein tests as he attempted to purify enzymes. His method of preparation was to adsorb the enzyme on kaolin, colloidal aluminum hydroxide, or colloidal phosphates of heavy metals. After impurities had been discarded, Willstatter eluted the enzyme from the colloid. He found that as he progressively purified the enzyme, positive color tests for protein became negative, although enzyme activity remained. In 1927 he said The protein therefore is no part of the enzyme. The protein in an enzyme solution, he thought, is merely a protective colloid on which the enzyme is adsorbed. Likewise, Willstatter con-... 

It has been shown that both the acid conditions used and the presence of molybdate can enhance hydrolysis of dissolved organic and condensed phosphates to give an overestimate of orthophosphate [91,92]. Similarly, colloidal phosphates in the filterable fraction may be molybdate reactive, which again will lead to an overestimation of the orthophosphate concentration [93]. Rigler observed that this overestimation of the true orthophosphate concentration may be as much as 10-100 times the true concentration of orthophosphate [94]. In attempts to avoid these hydrolytic effects, a "6-second extraction method" was developed in which phosphomolybdate formed was rapidly removed from the acidic environment [95], or excess molybdate was complexed with a citrate-arsenite reagent [96]. 

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