THE MOLYBDATE ASCORBIC-ACID BLUE METHOD FOR THE PHOSPHORUS DETERMINATION IN VERY DILUTE AND COLORED EXTRACTS BY SEGMENTED FLOW-ANALYSIS

A segmented flow analysis method for the determination of trace levels of orthophosphate is described. The method was based on the world wid e accepted procedure of Murphy and Riley, using ascorbic acid as reduc tant, allowing the use of the common automated systems with minor adap tations. 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 w as minimized by the optimization of the dialysis. The detection limit was 3 mu g/L. To prevent calcium sulphate precipitation, the use of H2 SO4 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 maintena nce procedure.