Molybdophosphate Lakes

Heleropoly adds will form highly coloured lakes with certain basic dyestuffs and these lakes can be used for colorimetric estimation of P. Best known of these are the coloured complexes formed with malachite green (14.15a) and crystal violet (14.15b), although several other complexes have been utilised (Chapter 12.8). Trace quantities 10-40 parts per billion of orthophosphate in water can 

FIGURE 14.1 Absorption spectra of heteropoly molybdenum blues. 

Colorimetric estimations are the most widely used method for the determination of soil P, after extraction with NaHCOj solution at pH = 8.5. Other applications are the estimation of P in metals, silicon, silicates, cements, coke, textiles, foodstuffs, fertilizers, lubricating oil additives, effluents and natural waters. 

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