The molybdate/ascorbic acid blue method for the phosphorus determination in very dilute and colored extracts by segmented flow analysis

Abstract

A segmented flow analysis method for the determination of trace levels of orthophosphate is described. The method was based on the world wide accepted procedure of Murphy and Riley, using ascorbic acid as reductant, allowing the use of the common automated systems with minor adaptations. A segmented flow system was built using a single 700 mm long dialysis path. The dialyzer was used to overcome the interferences due to organic and colloidal matter, often present in waste waters and 0.01 mol/L CaCl₂ or similar extracts of soils. The loss of sensitivity was minimized by the optimization of the dialysis. The detection limit was 3 μg/L. To prevent calcium sulphate precipitation, the use of H₂SO₄ to acidify the medium and the use of wetting agents with sulphate compounds was also prevented. No coating on the coil or on the tubing of the system was observed, decreasing the need of a frequent maintenance procedure.