Condensed phosphates analysis

P shows magnetic properties similar to 1H and 19F 31P with l = 1/2 exhibits sharp NMR peaks with chemical shifts extending over range of 700 ppm, 31P NMR has been used in the quantitative analysis of condensed phosphates, hydroxymethyl phosphines and thiophosphates. 

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... 

Since the labeling technique was introduced, a large number of further publications on the paper chromatography of phosphates have appeared (159), but these papers will not be considered separately here. They serve to confirm what was already partly known, and they describe improvements in technique, thereby reducing the risk of hydrolysis of the condensed phosphates in the acid medium used in chromatography. They also show how the accuracy of quantitative analysis could be increased (226). 

The most recent proposal for analysis of condensed phosphates depends on the examination of nuclear magnetic resonance spectra (43, 343). 

Reliable identification of polyphosphates often includes the Thilo and Wicker method of chromatographic analysis of the products of partial hydrolysis (Thilo and Wicker, 1957). In this approach, the hydrolysis of condensed phosphates in neutral solution at 60 °C yields... 

Y. Sekiguchi, A. Matsunaga, A. Yamamoto and Y. Inoue (2000). Analysis of condensed phosphates in food products by ion chromatography with an on-line hydroxide eluent generator. J. Chromatogr., 881, 639-644. 

Fig. 8-52. Analysis of condensed phosphates in detergents. - Separator column IonPac AS7 eluent 0.07 mol/L HN03 flow rate 0.5 mL/min detection photometry at 330 nm after reaction with ferric nitrate injection 50 pL of a 0.1% washing powder solution.

A quantitative analysis of the phosphate separated on the paper was done by Smith s method (42). Lucena-Conde and Prat s reagent (43) was successfully employed for the colorimetric determination of orthophosphate or condensed phosphates eluted from the sheet of paper. 

The hydrolysis of condensed phosphates during the orthophosphate analysis was virtually eliminated by minimizing contact time between the acidic reagents and the sample. Negative results were obtained when concentrated solutions of sodium tripolyphosphate were analyzed by this technique, however in the reactive phosphate technique of Strickland and Parsons (20)—a widely used oceanographic method—considerable hydrolysis of the polyphosphate took place. 

Even if the instrumental techniques gain ever more ground, some of them in automated form, evaluated and documented by computer, the simple, manual methods such as paper and thin-layer chromatography still have their role to play. One need only think of the separation of the various forms of phosphate such as orthophosphate, pyrophosphate, metaphosphate, polymeric phosphates and condensed phosphates, or the separation of polycyclic aromatic hydrocarbons (specifically with thin-layer chromatography) in water analysis. 

The analysis of condensed phosphates in the totally ionized form, especially together with standard inorganic anions, is possible only by utilizing gradient elution and suppressed conductivity detection, because the retention behavior... 

Application of the phosphorus-specific detection (see Sections 3.8.2 and 8.2.1.2) described by Vaeth et al. [142] allows the use of the AS7 column for the analysis of higher condensed phosphates. A mixture of potassium chloride and EDTA [143] is used as an eluent. The potassium chloride concentration determines retention EDTA is added only for improving peak symmetry. However, postcolumn derivatization with ferric nitrate, as mentioned above, cannot be applied in this case because the Fe(III) ions of the derivatization reagent form... 

---