RAPID-DETERMINATION OF DISSOLVED ORGANIC PHOSPHORUS IN SOIL LEACHATESAND RUNOFF WATERS BY FLOW-INJECTION ANALYSIS WITH ONLINE PHOTOOXIDATION

A rapid method suitable for the determination of dissolved organic pho sphorus (DOP) in soil leachates and runoff waters is presented. The fl ow injection (FI) manifold contains an in-line PTFE reaction coil wrap ped around a low power UV lamp and is based on the spectrophotometric determination of dissolved reactive phosphorus (DRP) and mineralised D OP at 690 nm after reduction of phosphomolybdate to molybdenum blue wi th tin(II) chloride. The linear range was 0-1.5 mg 1(-1) PO4-P, with a detection limit (3 s) of 7 mu g 1(-1) and a sample throughput of 40 h (-1) Tolerance to potential matrix interferences in soil pore waters, particularly Al(III), Si(IV), Fe(II) and Fe(III), was achieved using a combination of on-line sample pre-treatment by a strong acid ion exc hange column, low photoreactor pH and acid induced control of the kine tics of the molybdenum blue reaction. The results obtained with this m anifold were in good agreement with those obtained by a batch spectrop hotometric reference method. (C) 1997 Elsevier Science B.V.