Colorimetric determination of phosphorus in milk by flow injection analysis using a thermal/UV induced digestion

Two flow injection systems for the determination of total phosphorus in milk were developed: one for the determination of phosphorus using off-line digestion of milk and another with in-line digestion. The first procedure involves a classical Kjeldahl digestion of milk prior to introducing it into the flow system; the second uses acid, heat and UV-catalysed peroxodisulphate oxidation to convert in-line all forms of phosphorus compounds into orthophosphate, allowing a considerable amount of time to be saved. Concentrations of phosphorus in milk within the range of 706 to 984 mg P/L were found and FIA results were in good agreement with those provided by the reference method.