DETERMINATION OF PHOSPHATE IN SOLUTION AT DIFFERENT IONIC COMPOSITIONUSING MALACHITE GREEN

The malachite green method was sometimes used to determine low concent rations of inorganic phosphate due to its high sensitivity. The aim of this work was to test the suitability of this method for the determin ation of phosphorus (P) extracted by various reagents, e.g., KCl 0.01- 1.20M, CaCl2 0.01-0.1M, Na2SO4 0.01-0.40M, NaHCO3 0.1M at pH 8.5, and NaOH 0.1M+NaCl 1M. The malachite green method was also compared with t he traditional molybdenum blue method on 35 soil extracts. Color devel opment reached stability within 2 hrs and was stable for up to 24 hrs for dilute solutions. For concentrated solutions the stability was inv ersely proportional to the concentration of the reagent. Salt concentr ation appeared to have no effect on absorbance in KCl extracts of up t o 1.2M and in Na2SO4 extracts of up to 0.05M. Higher concentrations of sodium sulfate induced flocculation and precipitation of the dye comp lex, as did CaCl2 above 0.04 M. A strong correlation was found between the malachite green and the molybdenum blue method. The malachite gre en method can be used for P determination in soil extracts when approp riate time of color development is provided and salt concentration is taken into account.