Vanadomolybdate method

Phosphorus (dissolved orthophosphate plus dissolved organic phosphorus) Waste waters UV-irradiation for organic phosphorus oxidation to orthophosphate UV—Vis 0.08 mg L 1 Multi-pumping flow system vanadomolybdate method for detecting the orthophosphate [442]... 

The online photooxidative decomposition of phosphoms compounds to orthophosphate has also been applied to the determination of dissolved organic phosphoms (DOP) and TP in soil extracts and leachates, mnoff waters, natural, and wastewaters. For instance, the MPFS depicted in Figure 7.33 allows the spectrophotometric determination of dissolved orthophosphate and DOP in wastewater samples [106]. The determination of orthophosphate is based on the vanadomolybdate method. Inline ultraviolet photooxidation is employed to mineralize organic phosphoms to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow toward the UV lamp to carry out the determination of organic phosphoms. 

In the method for extractable phosphorus [62, 64-66] the phosphorus is extracted from the soil at 20 1°C with sodium bicarbonate solution at pH8.5. After filtration and release of carbon dioxide the extracts are introduced into a flow-injection system for the determination of phosphate. Phosphate is determined by reaction with vanadomolybdate and the yellow colour evaluated at 410nm. Between 20 and lOOOmg kg-1 phosphorus in soil has been determined using this method. 

The determination of phosphate concentration in a washing powder requires first the hydrolysis of the tripolyphosphate components into the phosphate ion or its protonated forms. Then a quantitative colorimetric method based upon the absorption of the yellow complex of phosphate and ammonium vanado-molybdate can be used. A series of standard solutions was prepared. The complex was then developed in 10 ml aliquots of these solutions by adding a 5.0 ml aliquot of an ammonium vanadomolybdate solution. 

Spectrophotometric methods are usually preferred for routine analysis of this parameter, most of them relying on the reaction between orthophosphate ions and molybdate in acidic medium in order to form a heteropoly acid. Color formation can be enhanced by adding vanadate to obtain the yellow vanadomolybdate complex (vanadomolybdophosphoric acid method) or by reducing the molybdo-phosphoric acid to yield strongly colored phosphomolybdenum blue species. 

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