COLORIMETRIC DETERMINATION OF PHOSPHORUS IN CITRATE-BICARBONATE-DITHIONITE EXTRACTS OF SOILS

Existing colorimetric methods for determining phosphorus (P) in citrat e-bicarbonate-dithionite (CBD) extracts from soils and sediments requi re pretreatments of extracts prior to the determination of the element . A method is proposed for the determination of P in CBD extracts with out any chemical treatments. Maintaining the citrate concentration bel ow 2.4 mM, maximum and stable absorbance develops in P-Mo-Sb system wi thin one hour and remains stable for 20 hours. An evaluation of potent ial interference was made by adding varying amounts of P to CBD extrac ts over a range of extractable iron (Fe) and aluminum (Al) levels. Nea r 100 percent recovery of the added P suggests the applicability of th e method to soils and sediments. Major advantages of the method are sp eed, simplicity, reliability and stability of the colored complex.