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A RAPID AND SENSITIVE METHOD FOR THE FLUORIMETRIC DETERMINATION OF PHOSPHATE BY FLOW-INJECTION

A rapid and sensitive fluorimetric method for the determination of phosphate by flow-injection analysis (FIA) has been developed. The determination is based on the following reaction: phosphate is firstly converted to 12-molybdophosphate in acid solution, which is then reacted with non-fluorescent thiamine at pH 9.0 to produce highly fluorescent thiochrome (The maximal excitation and emission wavelengths are 370 nm and 440 nm respectively.). Under the optimum operating conditions, a rather wide linear response range was obtained over the range of 0.02 mg L−1–20 mg L−1, with a detection limit of 0.01 mg L−1 (Signal/Noise = 3.0). The relative standard deviations (RSD) were 0.48%, 2.63% and 5.73% for 10 repeated analyses of 5.0 mg L−1, 0.5 mg L−1 and 0.05 mg L−1 of phosphate, respectively. The sampling throughput was 80 h−1. In addition, an automatic system was set up so that all the measurements could be accomplished by computer control. Phosphate in natural water samples was determined by the proposed method with good recovery rates.