Determination of low concentrations of organic phosphorus in soil solution

Phosphorus (P) export from agricultural land is an important source of wate r-quality deterioration in many areas of the world. Part of the total phosp horus in the soil solution is represented by dissolved organic P at concent rations that can be as low as 1x10(-6) Mof P. The suitability of four diges tion methods for the destruction of organic P and determination of orthopho sphate at low concentrations and small volumes using the malachite green me thod has been evaluated. The acid digestion procedures evaluated were 1) su lfuric and perchloric acid, 2) sulfuric acid and potassium persulphate, 3) nitric acid, and 4) nitric and perchloric acid. As inositol hexaphosphate ( IHP) represents one of the more resistant molecules to acid hydrolysis in s oils, this compound has been chosen to assess the recovery assay of the rec ommended procedure. The digestion procedures were adapted for the malachite green spectrophotometric method, in order to obtain lower analytical limit s for P determination. The sulfuric-perchloric acid digestion gave excellen t recovery and reproducibility, and can therefore be used for determining o rganic P in solution at concentrations as low as 6.45x10(-7) M.