INDEX orthophosphates

Calcium dihydrogen orthophosphate 1-hydrate crystallizes as large, white, shining, triclinic plates which may be up to 1 mm. in diameter. The refractive indexes for the crystals are 1.528, 1.518, and 1.501.1 No increase in weight is detectable when calcium dihydrogen orthophosphate... 

Figure 7.24. A. Relationship between 8 so values and the summed bond strengths of the oxygen atoms for a number of phosphates. Opien symbols denote orthophosphates, closed symbols denote higher phosphates. From Cheetham et al. (1986), by permission of the Royal Society of Chemistry. B. Relationship between the CSA for several orthophosphates and the geometrical distortion index (DI) of the phosphate group. From data of Turner et al. (1986a).

Properties Water-white to amber liquid depending on purity hygroscopic. D 1.20, refr index 1.420, bp (pure compound) 135-138C (1 mm Hg). Miscible with water and all organic solvents except aliphatic hydrocarbons hydrolyzed in water with formation of mono-, di-, and triethyl orthophosphates water solutions attack metals commercial material contains 40% TEPP. 

Anhydrous sodium trimetaphosphate is crystalline and water-soluble, but has no calcium-sequestering value. The trimetaphosphate is not precipitated by zinc, silver, or barium ions. Slow hydrolysis occurs in aqueous solution to give orthophosphate ions with intermediate formation of triphosphate ions. Conversion to triphosphate occurs very rapidly when the trimetaphophate is heated for a few minutes at 100° in the presence of an excess of sodium hydroude. No satisfactory quantitative method for its determination has been reported. It can, however, be identified by its refractive indexes, since the crystals are biaxial negative with a = 1.471, jS = 1.476, y = 1.480 ( .002). 

Quitasol and Krastins [504] used a polyhydroxyethylmethacrylate (Universal Anion, Grace Alltech, USA) as a stationary phase 5 mmol/L potassium nitrate adjusted to pH 3.5 with nitric acid serving as an eluent. Under these chromatographic conditions, the organic phosphate can be separated to baseline from orthophosphate and orthophosphite within 10 min. Because Quitasol and Krastins determined only the drug component in various pharmaceutical formulations, they used a refractive index detector for the sake of simplicity. This procedure can be validated in terms of precision, accuracy, and linearity without any difficulties. 

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