Flow-injection spectrofluorimetric determination of dissolved inorganic and organic phosphorus in waters using on-line photo-oxidation

The development and application of a continuous flow method for the rapid determination of inorganic and organic phosphorus in waters is proposed. The flowinjection (FI) system includes a simple ultraviolet photoreactor for the on-line photodegradation of organophosphorus compounds in the presence of peroxydisulphate, and an external decomposition unit for hydrolysing condensed phosphates with 0.5 mol l-1 hydrochloric acid. The fluorimetrically monitored product is thiochrome, which is formed by the oxidation of thiamine by phosphomolybdic acid. The FI configuration designed allows two injections to be performed for each sample; the first, without irradiation, corresponds to inorganic phosphorus and the second, with irradiation, total phosphorus (inorganic plus organic). Calibration graphs are linear up to 350 ng P ml-1 and the detection limit is 0.3 ng P ml-1. The results obtained with this FI system were in good agreement with those obtained by a batch spectrophotometric method.