Phosphate salts, solubility

Congruent phosphate programs are modifications of coordinated phosphate programs that operate at a Na P04 ratio lower than the normal 2.8 or 2.85 1. Experience has demonstrated that (contrary to theory) diminished phosphate salt solubility (phosphate hideout) takes place under high-load conditions. This is in addition to the recognized problems of high-temperature crystallization of TSP at the higher ratio of 3 1 (with the formation of some DSP and free caustic). 

Potassium Phosphates. The K2O—P20 —H2O system parallels the sodium system in many respects. In addition to the three simple phosphate salts obtained by successive replacement of the protons of phosphoric acid by potassium ions, the system contains a number of crystalline hydrates and double salts (Table 7). Monopotassium phosphate (MKP), known only as the anhydrous salt, is the least soluble of the potassium orthophosphates. Monopotassium phosphate has been studied extensively owing to its piezoelectric and ferroelectric properties (see Ferroelectrics). At ordinary temperatures, KH2PO4 is so far above its Curie point as to give piezoelectric effects in which the emf is proportional to the distorting force. There is virtually no hysteresis. 

Alkali Meta.IPhospha.tes, A significant proportion of the phosphoric acid consumed in the manufacture of industrial, food, and pharmaceutical phosphates in the United States is used for the production of sodium salts. Alkali metal orthophosphates generally exhibit congment solubility and are therefore usually manufactured by either crystallisation from solution or drying of the entire reaction mass. Alkaline-earth and other phosphate salts of polyvalent cations typically exhibit incongment solubility and are prepared either by precipitation from solution having a metal oxide/P20 ratio considerably lower than that of the product, or by drying a solution or slurry with the proper metal oxide/P20 ratio. 

Silver Phosphates. Silver phosphate [7784-09-0], or silver orthophosphate, Ag3P04, is a bright yellow material formed by treating silver nitrate with a soluble phosphate salt or phosphoric acid. Silver pyrophosphate [13465-97-9], is a white salt prepared by the addition of a soluble... 

Lead and Alloys Chemical leads of 99.9+ percent purity are used primarily in the chemical industiy in environments that form thin, insoluble, and self-repairable protective films, for example, salts such as sulfates, carbonates, or phosphates. More soluble films such as nitrates, acetates, or chlorides offer little protection. 

A patchy form of rust that attacks paint films from underneath, can be caused by sweaty hands, residues from fluxes, etc. Examples of the latter include residues from phosphating and soluble salts (including those from unsuitable rinsing water) and they can manifest themselves on steel in the form of a creeping filiform corrosion, i.e. as progressing threads of rust which loosen the coating. This can be followed visually through transparent films. It occurs, however, only when the relative humidity of the surround-... 

Urinary pH. The solubility of phosphate salts increases at lower pH values, while pH scarcely affects the solubility of Ca(C204) over a pH range of 5.7 to 7.5. Bacteria that metabolize urea contribute to an alkaline medium, thus decreasing the solubility of phosphates. 

Buffered tetrabutylammonium acetate (final pH 7.1) showed the best results, superior to the more popular phosphate salt, because of its high solubility in aqueous methanol and acetone and its fast reaction with chlorophylls to form hydrophobic... 

The example of amprenavir, an HIV-1 protease inhibitor, shows that intestinal metabolism can also be used as a strategy to enhance the bioavailability of compounds. In the biopharmaceutics classification system (BCS), amprenavir can be categorized as a class II compound it is poorly soluble but highly permeable [51]. Fosamprenavir, the water-soluble phosphate salt of amprenavir, on the other hand, shows poor transepithelial transport. However, after oral administration of fosamprenavir, this compound is metabolized into amprenavir in the intestinal lumen and in the enterocytes mainly by alkaline phosphatases, resulting in an increased intestinal absorption [51, 174],... 

The physical and chemical properties of elemental thorium and a few representative water soluble and insoluble thorium compounds are presented in Table 3-2. Water soluble thorium compounds include the chloride, fluoride, nitrate, and sulfate salts (Weast 1983). These compounds dissolve fairly readily in water. Soluble thorium compounds, as a class, have greater bioavailability than the insoluble thorium compounds. Water insoluble thorium compounds include the dioxide, carbonate, hydroxide, oxalate, and phosphate salts. Thorium carbonate is soluble in concentrated sodium carbonate (Weast 1983). Thorium metal and several of its compounds are commercially available. No general specifications for commercially prepared thorium metal or compounds have been established. Manufacturers prepare thorium products according to contractual specifications (Hedrick 1985). 

On the other hand, remineralisation may occur at such a rate that the surface layer is retained (Table 2). This requires continuous renewal of ions, either from among those newly solubilised or from those present anyway in the saliva. This process has been discussed in terms of thermodynamics, in particular of the solubilities of the various possible calcium phosphate salts [34]. The present authors are wary of this approach, as what is involved is essentially a kinetic... 

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. 

The elements have remarkably low specific gravity, and a high atomic volume (q.v.). The oxides and hydroxides are markedly basic they do not exhibit acidic qualities. The physical properties of the salts—solubility in water, molecular volume, optical properties, and the variation in the form of the crystals show the same order of variation as the atomic weights of the elements. Lithium differs in mafiy respects from the other members of the family. The salts of the alkali metals —nitrates, chlorides, sulphides, sulphates, phosphates, carbonates, etc.—are nearly all soluble in water, although lithium, carbonate, phosphate, and fluoride are very... 

If vitamins are added to a product to make a nutritional claim, it is critical that shelf-life studies are undertaken to prove that the overages added are sufficient to ensure that the label claims can be met at the end of product shelf life. This is important as none of the vitamins are fully stable in a soft drink environment and some, for instance vitamin C, are very quickly lost in the presence of oxygen. The addition of the fat-soluble vitamins to a soft drink also offers a formulation challenge to ensure that they are fully dispersed and that there are no problems with neck ringing during storage. Trace metals, particularly the transition elements, can also have a deleterious effect on vitamin shelf life, and sometimes metal scavengers, such as EDTA or phosphate salts, are added to improve the shelf life. 

Salt formation is often used to enhance the solubility of insoluble compounds. The very low intrinsic solubilities of these insoluble compounds coupled with weak basicity or acidity may make the solubility determination of these salts veryLdiblt. For example, the water solubility of the phosphate salt of a very insoluble compound GW1818X was determined to be 6.8 mg/mL and the pH of the saturated solution was 5.0 (Tong and Whitesell, 1998). The solubility at this pH was shown to be limited by the solubility of the base and did not adequately represent the solubility of the salt. One way to avoid this problem is to determine solubility in a diluted acidic solution using the same acid that formed the salt with the base. The solubility can then be estimated by correcting for the common ion effect from the acid. Keep in mind that it is only from a solubility experiment at a pH less than p x that the solubility of the salt can be estimated. 

Recent experiments to determine the dimension stabilizing efficiency of water soluble fire retardent chemicals (41) showed ammonium sulfamate to be superior to phosphate salts, giving anti shrink efficiencies of 51 to 66% compared to polyethylene glycol-1000 values of 63 to 77%. Sodium silicate, because of its alkalinity, caused collapse of the wood that resulted in negative anti shrink efficiencies. Strongly alkaline systems should hence be avoided. 

Figure 8.14 Changes in the content of nucleic acids, phospholipids, Pi and PolyPs, and the activities of exopolyphosphatase (PolyPase) and pyrophosphatase (PPase) during synchronous growth of Schizosaccharomyces pombe (Kulaev et al., 1973b) (a) 1, number of cells PL, phospholipids OP, P J P, total phosphate (b) PPi, acid-soluble polyphosphate PP2, salt-soluble polyphosphate (c) PP3, alkali-soluble polyphosphate PP4, hot-perchloric-acid-soluble polyphosphate JZPolyP, total polyphosphate.

In the same way, organic bases such as amines can be dissolved by lowering the pH. Codeine (7,8-didehydro-4,5-epoxy-3-methoxy-17-methylmorphinan-6-ol) is a commonly used painkiller. Codeine itself is not very soluble in water but it does contain a basic nitrogen atom that can be proto-nated to give a more soluble salt. It is usually encountered as a phosphate salt. The structure is com-... 

The above discussion indicates that acidic phosphate salts may play an important role in forming CBPCs. To use acid phosphates as the acidic components in acid-base reactions, primary requirement is solubility in water. Table 4.1 lists solubilities of some of the common hydrogen phosphates that are available in the literature and are useful intermediate phases during formation of CBCs. 

In addition to these acid phosphates, Sugama and Kukacka [5] also used (NH4)2HP04 which is an alkaline phosphate to react with MgO and produce ceramics. Such monohydrogen phosphate salts may often be used because their solubility is lower than the dihydrogen phosphates, but generally, the solubility of such salts, except for that of ammonium, is too low. Furthermore, these are not acid salts and hence the reaction with an oxide is not an acid-base reaction. For these reasons, detailed discussion of these salts is not included here. 

In forming CBPCs, this dissociation is essential. The cations formed by dissociation react with phosphate anions that are present in the aqueous solution and form phosphate salt molecules. These salt molecules connect to each other and form a network and consolidate into a crystalline phosphate ceramic. Thus, success in forming CBPCs lies mainly in successfully dissociating sparsely soluble oxides in acidic solutions and precipitating salt in crystalline form. We wiU discuss the fundamentals of this dissociation in the next several chapters and present methods of dissociating various oxides in phosphate solutions to form ceramics. 

The plots in Fig. 5.2 show that (Mg " (aq)) decreases linearly as the pH increases. Thus, its solubility in H3PO4 solution is high, but will be significantly less if acid phosphate solutions of higher pH are used to form the ceramics. For this reason, as stated above, acid phosphate salts are used in fabrication of almost all Mg-phosphate ceramics. 

Since calcium oxide is more than sparsely soluble and its reaction with phosphoric acid or a soluble phosphate is highly exothermic, researchers have used less soluble salts of calcium to react with the phosphates and form a phosphate ceramic [4-12]. In the acidic medium of the phosphate solutions, the salts of calcium dissolve slowly and release Ca (aq) into the solution, which subsequently reacts with phosphate anions and forms calcium phosphates. The best calcium minerals for forming CBPCs are combination of oxides of calcium and insoluble oxides such as silica or alumina, e.g., calcium silicate (CaSi03) and calcium aluminate (CaAl204), or even a phosphate of calcium such as tetracalcium phosphate (Ca4(P04)2 0). These minerals are reacted with acid phosphate salts to form phosphate cements. 

Note in Fig. 13.2 that the solubility of monocalcium silicate is higher than that of the corresponding aluminate at any pH > 3. In the acidic region that is of interest for forming CBPCs, both may be considered as sparsely soluble, and if they are reacted with a phosphate salt, ceramics may be formed. Thus, monocalcium silicate and aluminate are starter minerals to form calcium phosphate ceramics. 

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