Spectrophotometric determination of dissolved organic phosphorus in natural waters using in-line photo-oxidation and flow injection

A rapid in-line photochemical digestion for use with flow injection (Fl) to determine the dissolved organic phosphorus (DOP) in natural waters is described. The Fl system includes a simple ultraviolet (UV) photoreactor and uses the tin(II) chloride reduction of phosphomolybdate for the spectrophotometric determination of the dissolved reactive phosphorus (DRP) produced by the photo-oxidation. Samples in the range 0.1–4 and < 0.1 mg l–1 of P can be analysed at rates of 72 and 50 samples h–1, respectively. The effective detection limit of the technique was 0.01 mg l–1. Comparison of the results for DOP obtained using the proposed method were in good agreement with those obtained using standard methods. The DRP could also be determined using the same Fl manifold but without UV irradiation.