Multi-pumping flow system for the determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples

A multi-pumping flow system (MPFS) for the spectrophotometric determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples is proposed. The determination of orthophosphate is based on the vanadomolybdate method. In-line ultraviolet photo-oxidation is employed to mineralise organic phosphorus to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow towards the UV-lamp to carry out the determination of organic phosphorus. Calibration was found to be linear up to 20 mg P L^-1, with a detection limit (3s_b/S) of 0.08 mg P L^-1, an injection throughput of 75 injections h^-1 and a repeatability (R.S.D.) of 0.6% for the direct determination of orthophosphate. On the other hand, calibration graphs were linear up to 40 mg P L^-1, with a detection limit (3s_b/S) of 0.5 mg P L^-1, an injection throughput of 11 injections h^-1 and a repeatability (R.S.D.) inferior to 2.3% for the procedures involving UV photo-oxidation.