Solubility calcium phosphate

Again, there are several choices of extractant, and the preferred one depends mainly on the type of soil under test. One of the most widely used procedures is the Olsen method (Olsen ef al., 1954), which was developed in the USA to correlate crop response to fertilizer on calcareous soils. The amount of P extracted will vary with temperature (increases by 0.43 mg P kg- per degree rise between 20°C and 30°C) and shaking speed, so conditions should be standardized. The extractant is 0.5 M sodium bicarbonate adjusted to pH 8.5. The bicarbonate competes with phosphate on the adsorption sites extracts, and removes most, but not all of it, together with some soluble calcium phosphate. Addition of phosphate-free activated carbon before shaking is necessary if coloured soil extracts are obtained, and then they will require filtration. 

Addition of alkali has the opposite effect, and at about pH 11 almost all the soluble calcium phosphate occurs in the colloidal phase. These changes are not reversible on subsequent dialysis against untreated milk. 

Freezing milk causes crystallization of pure water and the unfrozen liquid becomes more saturated with respect to various salts. Some soluble calcium phosphate precipitates as Ca,(POj2, with the release of H+ and a decrease in pH (e.g. to 5.8 at — 20°C). 

Decrease in pH. After heating at 140°C for 20 min, the pH of milk has decreased to about 5.8 due to acid production from pyrolysis of lactose, precipitation of soluble calcium phosphate as Ca3(P04)2, with the release of H+, and dephosphorylation of casein with subsequent precipitation of the liberated phosphate as Ca3(P04)2 with the release of H+. The heat-induced precipitation of Ca3(P04)2 is partially reversible on cooling so that the actual pH of milk at 140°C at the point of coagulation is much lower than the measured value and is probably below 5.0. 

Precipitation of soluble calcium phosphate as Ca3(P04)2 with the release of H+. After heating at 140°C for 5-10 min, most (> 90%) of the soluble phosphate has been precipitated. 

Milk contains a range of groups which are effective in buffering over a wide pH range. The principal buffering compounds in milk are its salts (particularly soluble calcium phosphate, citrate and bicarbonate) and acidic and basic amino acid side-chains on proteins (particularly the caseins). The contribution of these components to the buffering of milk was discussed in detail by Singh, McCarthy and Lucey (1997). 

The measurement of pH in cheese making is extremely important to control fermentation/acid production and hence the final quality. While there are no standard methods available for measuring cheese pH, there have been few methods reported in the literature. One method involves preparing a slurry of 10 g of grated cheese in water and measuring the pH potentiometrically (Fox et al., 2004a). However, this method may alter the balance between colloidal and soluble calcium phosphate and hence it is preferable to measure the pH of the cheese directly. The quinhydrone electrode method (Marshall, 1992) measures the pH directly. The potential (mV) created by a paste of cheese and quinhydrone in saturated KC1 is measured and used to determine the pH at a particular temperature. 

Electrolytic Methods.—If apatite or other phosphatic material is placed round the anode in a solution of sodium chloride which is being electrolysed, a citrate-soluble calcium phosphate is precipitated. Or perchloric acid may be made separately in the anode compartment and mixed with the alkali produced at the kathode, giving a precipitate of Ca2H2P2Og.2... 

The deposition of sparingly soluble calcium phosphates on PHEMA hydrogels, both in vitro and in vivo, can be modified by the incorporation of citric acid into the PHEMA hydrogels. In the presence of citrate anions the formation of hydroxyapatites was prevented. The calcium phosphate deposits which formed in vitro on PHEMA were mainly monocalcium phosphate monohydrate and dicalcium phosphate dihydrate. The types of deposits formed in vivo were quite different from those formed in vitro. The in vivo deposits formed on PHEMA were mostly hydroxyapatites deficient in calcium and hydroxyl ions. Citrate anions were also observed to prevent significantly the deposition in vivo of protein onto PHEMA hydrogels. 

Eh In mineral soils dominated by iron, minerals associated with phosphorus are stable under aerobic or drained soil conditions. As the soil undergoes reduction, a decrease in Eh increases phosphorus solubility through reduction of FeP04. Accumulation of organic acids and dissolved carbon dioxide can also potentially increase the solubility calcium phosphates. 

Similarly influence the soluble fluorides for example the F ions released from NaF to the solution form the insoluble CaFj which covers the cement grains. The complex fluorosilicates Na2SiFg and NajAlFg can additionally result in the precipitation of siUcate or aluminate gel on the surface of cement grain poor in calcium. Phosphogypsum, soluble calcium phosphates and sodium fluoroaluminates containing by-products exhibits the retarding effect too [96]. 

Slightly soluble calcium phosphates can be used to control the availabiUty of Ca " in the formation of calcium pectinate or calcium alginate gels. In this way, optimum performance can be obtained in their use in jams, jellies, aqueous desserts, and so on. The beneficial effects from alginates, combined with phosphates, on the properties of ice cream and frozen desserts have been known for some time [104,105]. 

Hydroxyapatite is the most stable and, at neutral pH, least soluble calcium phosphate. Calcium hydrogen phosphate, which is readily formed by precipitation, is considerably more soluble. 

Solid phase Cells Soluble calcium phosphates... 

Interestingly, the composition, phase, morphology, and placement of hydroxyapatite will influence the speed and extent of bone growth. Since the resorption process is siuface-driven by the adsorption of osteoblasts, the ultimate solubility of a ceramic will be directly related to its surface area - i.e., crystal size and density. In addition, careful cmitrol of processing parameters is necessary to prevent thermal decomposition of hydroxyapatite into other soluble calcium phosphate phases (e.g., tricalcium phosphate, Ca3(P04)2, tetracalcium phosphate, Ca4(P04)20, and CaO), which... 

Polyphosphate inhibitors induce fllm formation. They form complexes with calcium ions. Above pH 7.5, the complexes are transformed into orthophosphates, which convert into poorly soluble calcium phosphate at higher temperatures. Polyphosphate has low toxicity, but increases the eutroph-... 

Besides, biphasic calcium phosphate (BCPs) are bioceramics consisting of two different calcium phosphate phases which are mixed. Typically, BCI used in nanoconq)osites aimed at bone regeneration consist of a low solubility calcium phosphate phase such as hydroxy atite (HA) and a more soluble one such as beta-tricalcium phosphate (TCP) [22]. MSCs, mesenchymal stem cells OCP, octacalcium phosphate. 

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