Phosphate gravimetric analysis

Analysis. Excellent reviews of phosphate analysis are available (28). SoHds characterization methods such as x-ray powder diffraction (xrd) and thermal gravimetric analysis (tga) are used for the identification of individual crystalline phosphates, either alone or in mixtures. These techniques, along with elemental analysis and phosphate species deterrnination, are used to identify unknown phosphates and their mixtures. Particle size analysis, surface area, microscopy, and other standard soHds characterizations are useful in relating soHds properties to performance. SoHd-state nmr is used with increasing frequency. 

For a precipitate used in gravimetric analysis magnesium ammonium phosphate has a rather high solubility (0.1 g dm 3 in water at 20°C). Hence solution volumes should be kept as low as possible and the precipitate must be filtered from cold solution. Furthermore, the solution composition must be carefully controlled to ensure the maintenance of conditions of... 

In these, As04 tetrahedra are built into the polyphosphate chains (309). Since the P—0—As bond has much the same sensitivity to hydrolysis as the As—0—As bond, they are rapidly hydrolyzed in aqueous solution to monoarsenate and mixtures of polyphosphates, the mean chain length of which depends on the As P ratio in the starting material (74)- Contrary to an idea based originally on gravimetric analysis (309), the As atoms are not distributed regularly in the chain, but statistically (308). The observation that, after careful hydrolysis, the phosphate content is exclusively in the form of polyphosphates provides chemical proof of catenation in the poly-arsenatophosphate anions. When arsenatophosphates with more than five P atoms per atom of As are hydrolyzed by hot water trimetaphosphates are formed, just as they are formed for all other high-molecular polyphosphates in solution (316). 

A polyvinyl acetate latex prepared by semi-continuous polymerization at 55° using a polymethacrylic acid-nonylphenol-poly-ethoxylate phosphate ester emulsifier and sodium persulfate-sodium formaldehyde sulfoxylate initiator (23). The latex was cleaned by ion exchange and serum replacement using both Nuclepore and Pellicon membranes, and the cleaned latex and serum fractions were analyzed by conductometric titration. In addition, the dried films were extracted with water and organic solvents, and the extracts were analyzed by infrared spectroscopy and thermo-gravimetric analysis. 

Fig. 8 Thermal gravimetric analysis of dicalcium phosphate dihydrate.

Pyrolysis curves of lead derivatives. 9) Sulphide. 10) Sulphl 11) Hydrogen phosphate. 12) Carbonate. 13) Basic thiocyanate. 14) Oxalate. 15) Phthalate. Reproduced from C. Duval, "Thermo-gravimetric Analysis". Elsevier Publishing Co., Amsterdam (1953) p. 466. 

Basic magnesium phosphates may be characterized by x-ray and thermo-gravimetric analyses and elemental analysis. Magnesium may be determined... 

Since all condensed phosphates are ultimately degraded to monophosphate in hot solution, especially at low pH, the total phosphorus(V) content of a substance may readily be determined after hydrolysis either gravimetrically or titrimetrically (109). However, as soon as it is a question of estimating the content of separate components in mixtures of condensed phosphates insuperable difficulties are encountered if methods depending on precipitation, titration, or a combination of the two are used. Even a quantitative precipitation of monophosphate is impossible if polyphosphates with chain length of n = 3 or more arc present in the solution. The precipitating cation and the compound to be precipitated by it are partly kept in solution by the polyphosphate part of the polyphosphate is also carried down by the precipitate. Both of these effects depend in their extent in different ways on the nature and quantity of the substances present and the analysis gives a correct quantitative result only in isolated instances... 

Phosphorus can serve as a benehcial adjunct or as a deleterious agent. There are several test methods for the determination of phosphorus. In addition to the three test methods described here, reference should also be made to multielement analysis methods such as inductively coupled plasma atomic emission spectroscopy (ICPAES) (ASTM D-4951, ASTM D-5185) and X-ray fluorescence (XRF) (ASTM D-4927, ASTM D-6443) described above in this guide. Phosphorus can also be determined by a photometric procedure (IP 148) or by a test method (ASTM D-1091) in which the organic material in the sample is destroyed, phosphorus in the sample is converted to phosphate ion by oxidation with sulfuric acid, nitric acid, and hydrogen peroxide, and the magnesium pyrophosphate is determined gravimetrically. Another method (ASTM D-4047, IP 149) in which the phosphorus is converted to quinoline phosphomolybdate is also available. 

To increase the precision of quantitative analysis, the plasticizer sample is diluted with carbon disulfide, its infrared absorption measured, and compared with absorptions standard of standard samples prepared also in CS2 to cover the range of concentrations from 0.5 to 3 mg/ml. For each suspected (identified) plasticizer, a series of standards has to be prepared and measured. It is also important to select a suitable wavelength for quantitative analysis. For dioctyl phthalate bands at 1725 and 1121 cm" are usually used. For tricresyl phosphate band at 1191 cm is used. Similar to gravimetric method, the results are subject to various interferences when mixtirres of plasticizers or mixture of plasticizers with other additives ate used. 

A crystalline precipitate of magnesium ammonium phosphate hexahydrate (struvite) is produced when other magnesium salts are added with ammonia to weakly basic or neutral phosphate solutions (5.39). The ignition of this salt to give the pyrophosphate forms the basis of a gravimetric method of analysis for P (Chapter 14.1). 

All the experiments were performed in a water thermostat. Equilibrium was ascertained by repeated analysis of the liquid phase, which was separated from the solid phase by filtration through a mat of platinum wires. Phosphate was determined gravimetrically as Mg2P2 7 Sodium was determined as Na2S04 after phosphoric acid had been removed as lead phosphate. 

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