Calcium phosphate solubility product

Some signs and symptoms of hyperphosphatemia are a result of the low solubility of the calcium-phosphate complexation product. Calcium-phosphate crystals are likely to form when the product of the serum calcium and phosphate concentrations exceeds 50 to 60 mg2/dL2. 

Calcium Phosphates. The alkaline-earth phosphates are generally much less soluble than those of the alkaH metals. Calcium phosphates include the most abundant natural form of phosphoms, ie, apatites, Ca2Q(P0 3X2, where X = OH, F, Cl, etc. Apatite ores are the predominant basic raw material for the production of phosphoms and its derivatives. Calcium phosphates are the main component of bones and teeth. After sodium phosphates, the calcium salts are the next largest volume technical- and food-grade phosphates. Many commercial appHcations of the calcium phosphates depend on thek low solubiHties. 

C18-0073. For the following salts, write a balanced equation showing the solubility equilibrium and write the solubility product expression for each (a) silver chloride (b) barium sulfate (c) iron(H) hydroxide and (d) calcium phosphate. 

The product, Ca(H2P04)2, is more soluble than the phosphate. Sulfuric acid is produced in the largest quantity of any compound, with production that approaches 100 billion pounds annually. Approximately two-thirds of this amount is used in the production of fertilizers. The mixture containing calcium dihydrogen phosphate and calcium sulfate (gypsum) is known as superphosphate of lime, and it contains a higher percent of phosphorus than does calcium phosphate. 

Pertinent calcium phosphates relevant to aqueous systems, their formula, structure and negative logarithm of the solubility product pK... 

A different application of visible microscopy was pioneered by Gomori. In 1941 he showed that alkaline phosphatase could be specifically located by its hydrolysis of soluble phosphate esters (initially glycerophosphate). If calcium ions were present in the medium in which the sections were incubated, insoluble calcium phosphate precipitated as a result of the action of the hydrolase. The site of the precipitate could be visualized if cobalt or lead salts were subsequently added to replace calcium and the sections exposed to hydrogen sulfide. In principle many hydrolases and other enzymes could be studied using the appropriate substrates and precipitants. It was important to ensure that the products of the enzyme reactions did not diffuse from the sites where the enzymes were located. It was also essential that the reagents could reach the enzyme site. 

Fluorapatite is a highly insoluble calcium phosphate phase. The solubility product of stoichiometric fluorapatite at 37°C is 3.19 0.14x10 " mol 1 (for Cas(P04)3F as reported by Moreno et al. [53]) and appears significantly lower than that of HA in the same conditions (7.36 0.93 x 10 ° mol for Ca5(P04)30H). Asuggested explanation for this very low solubility product is that cohesive forces are stronger in fluorapatite than in other apatites due to smaller unit-cell dimensions. The complete solid solution Ca-,o(P04)6(OH)2-xFx can be obtained. Initial solubility determinations have shown a solubility minimum for x close to 1 [54], related to the formation of hydrogen bonding between F and OH ions. These results were subsequently... 

The stabilizing effect of buffers that have multiple charged species in solution should also be investigated to determine the potential reaction between excipients and API. For example, buffers that use carbonates, citrate, tartrate, and various phosphate salts may precipitate with calcium ions by forming sparingly soluble salts. However, this precipitation is dependent upon the solution pH. Because phosphate can exist in mono-, di-, and tribasic forms, each calcium salt has its own solubility product, and precipitation will only occur when one of the solubility product is exceeded. Calcium ions may also interact or chelate with various amino acids, and other excipients, which may also lower the effective concentration of calcium that is capable of interacting with phosphate ions. Finally, the activity of phosphate ions may be lowered due to interactions with other solution components. 

Milk serum is supersaturated with calcium phosphate, the excess being present in the colloidal phase, as described above. The balance between the colloidal and soluble phases may be upset by various factors, including changes in temperature, dilution or concentration, addition of acid, alkali or salts. The solubility product for secondary calcium phosphate, [Ca2+][HPOr] is about 1.5 x 1(T5 or pKs = 4.85. 

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. 

The mechanism by which the mineral leaves the mitochondrion is only one of the problems of this theory. The mineral in the mitochondrion exists in association with the fluid contents. Thus, unless this water is in some structural form with abnormal solubilities, the mineral must be saturating the fluid, and solubility products apply. It follows that the mitochondrial calcium and phosphate concentrations must be similar to those of the extracellular fluids, i. e. calcium must be concentrated thousandfold to overcome the low intracellular values. 

Three approaches have been used in attempting to account for the buffer behavior of milk in terms of the properties of its components. These are calculation, fractionation, and titration of artificial mixtures. Whittier (1933A.B) derived equations for dB/dpH in calcium phosphate and calcium citrate solutions, taking into account available data on dissociation constants and solubility products. Presumably this approach could be extended to calculate the entire buffer curve. It demands precise knowledge of the dissociation constants of the several buffers, the dissociation of the calcium and magnesium complexes, and the solubility products of the calcium and magnesium phosphates under the conditions of a titration of milk. 

This relationship varies slightly because of the vertical fluctuation in the phosphorus content in the sea. For saline water systems, data on the solubility product of a calcium phosphate is difficult to obtain inasmuch as — aside from temperature and hydrostatic pressure — the solubility product is dependent on the type and amount of solutes present. The apparent dissociation constants of H3P04 are defined by the equations129,130 ... 

No reliable estimates presently exist on the degree of saturation of sea water with respect to calcium phosphate. The apparent solubility product reported in the literature131 ... 

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. 

An independent means of establishing the chemical nature of the colloidal calcium phosphate is provided by the form and magnitude of the solubility product that governs the equilibrium between the ions in the milk serum and the solid phase. A thermodynamic model of the equilibria can be constructed as follows. First, ions in solution are supposed to be in equilibrium or quasi-equilibrium with a calcium... 

The divalent mineral-binding effect of CPPs can be put in use in applications where one wants to increase the availability for absorption of these minerals in the gut. Drinks with calcium and iron are examples for commercial uses of CPPs examples can be found especially in the Japanese market. Products for children that incorporate calcium or milk minerals and CPPs in sweets or cookies are found in the South Asian market. As mineral accretion is high during early childhood, incorporation of CPPs provides good solubility and availability for absorption of calcium or zinc and thus is worth considering for infant nutrition. Other possible uses are in calcium-enriched dairy products and natural calcium supplements. In addition, dental applications are obvious, since complexes of calcium, CPPs and phosphate may reduce caries in a dose-dependent fashion. 

Alternatively, antisealants can be used to control calcium carbonate scale at LSI values as high as 2.0-2.5, depending on the specific antisealants. Calcium also forms scales with fluoride, sulfate, and phosphate. The LSI will not help predict these scales analysis of water quality, using the ion product and solubility constants, is required to determine the potential for scaling with calcium fluoride or calcium phosphate. Antisealants currently available can address calcium fluoride and calcium sulfate scale they do not address calcium phosphate scale (although newer antisealants will be available in the near future to address this scale). 

Calcium phosphate has become a common problem with the increase in treatment of municipal waste-water for reuse. Surface waters can also contain phosphate. Calcium phosphate compounds can contain hydroxyl, chloride, fluoride, aluminum, and/ or iron. Several calcium phosphate compounds have low solubility, as shown in Table 7.2. Solubility for calcium carbonate and barium sulfate are also shown by comparison. The potential for scaling RO membranes with the calcium phosphate compounds listed in Table 7.2 is high and will occur when the ion product exceeds the solubility constant. This can occur at orthophosphate concentrations as low as 0.5 ppm. Sodium softening or antisealants together with low pH help to control phosphate-based scaling. 

Enormous quantities of phosphorus compounds are used in the production of fertilizers. Calcium phosphate is found in many regions of the world, but its direct use as a fertilizer is not very effective because of its low solubility. As was mentioned in Chapter 1, sulfuric acid plays an important role in fertilizer production and approximately 65% of the sulfuric acid manufactured (more than 80 billion pounds annually) is used for this purpose. 

If a good deal of the organic protein (ossein) has been left in the bone, as is the case when the fat has been extracted by solvents, and not by steaming, the resulting bone-meal quickly decomposes in the soil, the phosphoric acid being made partly soluble by the decomposition products of the proteins. Such a bone-meal will contain (approximately) 45 per cent, of calcium phosphate, 1-5 per cent, of magnesium phosphate and over 30 per cent, of organic matter. 

It is also deposited when any aqueous solution of calcium phosphate is evaporated to dryness with hydrochloric acid. It occurs as an anhydrous more soluble form and as a hydrated less soluble crystalline form (monoclinic needles). The solubility product [Ca++][HP04 =] is... 

Calcium Phosphate Compounds and their Solubility Product Constants (p/sTsp). 

In discussions of the precipitation of calciinn phosphate, the phase which is usually emphasized is the thermodynamically most stable, HAP. However, most calcium phosphate solutions in which precipitation experiments are made, are initially supersaturated with respect to four additional phases. The solubility isotherms are shown in Figure 1 as a function of pH. Thus, at a pH of 7.0, in order of increasing solubilities, it is necessary to take into account tricalcium phosphate (Ca3(PO )2 hereafter TCP), octacalcium phosphate (Ca H(PO ). 2 1/2 H2O, hereafter OCP), anhydrous dicalcium phosphate (CaHPO, hereafter DCPA), and dicalciiam phosphate dihydrate (CaHPO. 2H2O, hereafter DCPD). The corresponding thermodynamic solubility products. 

---