Sodium tripolyphosphate, control

Sodium tripolyphosphate is produced by calcination of an intimate mixture of orthophosphate salts containing the correct overall Na/P mole ratio of 1.67. The proportions of the two anhydrous STP phases are controlled by the calcination conditions. Commercial STP typically contain a few percent of tetrasodium pyrophosphate and some trimetaphosphate. A small amount of unconverted orthophosphates and long-chain polyphosphates also may be present. 

To produce sodium tripolyphosphate, a definite temperature control is necessary. When monosodium phosphate and disodium phosphate in correct proportions, or equivalent mixtures of other phosphates, are heated for a substantial time between 300 and 500°C and slowly cooled, the product is practically all in the form of the tripolyphosphate. 

In sequestration (chelation) the hardness ions are bound to the builder in the form of soluble complexes. Phosphates, citrates, and nitrilotriacetic acid (NTA) are examples of this class of builder compound. Table 8.3 lists the calcium binding capacities of various builders. Other strongly chelating compounds exist, such as phosphonates and EDTA, but they are generally not extensively used in HDLDs. The most efficient builder is sodium tripolyphosphate (STPP). Unfortunately, tripolyphosphate has been identified as a possible cause of eutrophication in lakes and rivers. It is severely controlled and even banned in several countries. As a result, most countries in North America and Europe have converted to nonphosphate formulations. Other regions are also gradually imposing restrictions on the use of phosphates. 

A controlled potential coulomctric titration has also been developed for the determination of technetium. Pertcchnetatc was titrated in an acetate buffered (pH 4.7) aqueous solution of sodium tripolyphosphate (NasP-.Oio) at a potential of-0.70 V vs SCE. Under these conditions TcOj was found to be quantitatively reduced to Tc(lII). In the range of 0.5-5 mg of titrated TCO4, the relative error of the method was about 1 % and the relative standard deviation 0.5%. The ions Fc(lll), Mo(Vf), Ru(fV), U(V1). V(IV), F , and NOs" interfere strongly. Technetium can be removed from these ions by distillation from cone, sulphuric acid solution [102[. 

Sodium hexametaphosphate is one of a series of chain polymers termed polyphosphates, and threshold treatment using various members of the series has found extensive use in controlling calcium carbonate scale formation. Veale [1984] states that typically 5 mg/l of polyphosphate will inhibit the precipitation of 500 mg/l of CaCOy To control scale in sea water evaporation an additive mixture could include sodium tripolyphosphate, lignin sulphonates and an antifoaming agent. 

Practical laundry detergent formulations usually include builders for control of polyvalent metal ion activities so that the relevant salts of the anionic surfactant, which is usually present, are not precipitated out of solution. The presence of builders also has implications for the effectiveness of antifoam action because they may prevent the precipitation of calcium soaps. We can illustrate the relevant issues if we consider, for example, the concentration of calcium harduess uecessary to just initiate calcium soap precipitation in the case of a solution built by sodium tripolyphosphate at a pH >10.5. If we iguore the effect of solubilizatiou of soaps and calcium binding in anionic surfactant micelles, then, according to Irani and Callis [4],... 

Figure 9.24(a) Apparent viscosity, zeta potential, amount of adsorption, and pH in zinc oxide-water (50/50) suspensions versus initial concentration, c, curves for Na salt of polyacrylic acid (PA) (O), Na salt of formalin condensate of -naphthalene sulphonate acid (NSF) (C), and sodium tripolyphosphate ( ). The initial concentrations of PA and NSF refer to the mole concentrations expressed/monomer unit of them. A dotted line refers to the apparent viscosity versus c curve for PA at a controlled pH of 10.1. C = initial mole concentration of surfactant and polyphosphate, (b) Apparent viscosity, zeta potential, amount of adsorption, and pH in zinc oxide-water (50/50) suspensions versus initial concentration, c, curves for Na salt of formalin condensate of alkyl (C4) naphthalene sulphonic acid (Al-NSF) (Ci), sodium alkyl (C4) naphthalene sulphonate ( >), and sodium dodecyl benzene sulphonate (O). The initial concentrations of Al-NSF refer to the mole concentrations expressed/monomer unit. C = initial mole concentration of surfactant. From [61] with permission. 

After the synthesis, impurities of sodium, chlorine, pyrophosphate ions and unreacted tripolyphosphate ions remained in the colloidal solutions that can affect optical properties and stability. Thereby, after the synthesis the solution was purified with dialysis membranes (cut-off 12 kD). The purification efficiency was controlled by the measurement of the dialysate electroconductivity. During the first hour of dialysis, a slight increase in dialyzates electroconductivity occurs. After 24 h, the electroconductivity of dialysate and distilled water became equal. During the whole time of dialysis the terbium luminescence intensity was constant. 

Chitosan was also formulated in a controlled-release protein delivery system using bovine serum albumin (BSA) as a model drug. Chitosan was reacted with sodium alginate in the presence of tripolyphosphate for bead formation [94]. Parenteral administration of proteins/peptides requires repeated injections because of their extremely short biological half-life. Daily multiple injections are highly risky and require close medical supervision. On this basis, bovine serum albumin (BSA)-loaded chitosan microspheres were prepared to test the drug release behavior in buffers with different pH values. BSA-chitosan microspheres with particle sizes in the range from 5 to 10 pm... 

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