Determination of total phosphorus in waters and wastewaters by on-line microwave-induced digestion and flow-injection analysis

Abstract

An on-line flow-injection system for the determination of total phosphorus in waters and wastewaters is described. Digestion was performed using a flow-through reactor in a modified domestic microwave oven, and the orthophosphate formed was detected as phosphomolybdenum blue after on-line filtration. The modifications and operation of the microwave complied with Australian Standards. Reagent and digestion conditions required to give optimal oxidation and hydrolysis of organic and condensed model species are reported. The flow-injection method gave complete recovery for almost all the model P compounds tested, with the exception of condensed phosphates. When the proposed method was applied to a series of wastewater samples, the results obtained were in close agreement with those from a conventional batch digestion method. The technique was rapid (7 samples h −1, 4 replicates), with a linear range of interest for wastewaters 0–18 mg P 1 −1, and a detection limit of 0.09 mg P 1 −1.