Abstract

A. K. Biswas and K. P. Tomar

Malachite green method is by far the most sensitive spectrophotometry method for estimation of P in soil-water and other extracts. The phosphomolybdo-dye colour intensity and the colour stability are greatly influenced by the solution acidity and the concentration of polyvinyl alcohol (PVA). Optimum combinations of H2SO4 acidity and PVA required to stabilize the coloured complex have been evaluated in this study. A minimum PVA level of 0.04 percent (w/v) and a minimum acidity of 0.4N H2SO4 have been recommended to prevent agglutination and precipitation of the coloured complex. The acid stability plateau at a PVA concentration of 0.06 per cent was between 0.8 and 1.2N H2SO4 at all P levels. The plateau moves slightly towards lower normality of H2S04 at higher PVA concentrations. At 1 .ON H2SO4 and 0.06 percent PVA, the Beer-Lambert law was excellently followed by the coloured complex up to 0.4 mg P L^-1 when absorbance was recorded at 635 nm wavelength using 1-cm path length cells.

spectrophotometry; agglutination; polyvinyl H2SO4

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