Photometric determination of phosphorus in niobium steel with molybdenum blue method

Abstract

A photometric determination of phosphorus in niobium steel with molybdenum blue has been studied. The established procedure is as follows: 0.5 to 1 g of sample is decomposed with 10 ml of aqua regia, to this is added 10 to 15 ml of perchloric acid and it is evaporated until nitric acid is removed fuming perchloric acid vigorously.
After cooling, the solution is diluted to approximately 50 ml with hot water, to this 10 ml of hydrofluoric acid (1+4) is added. It is then heated, and 4 g of boric acid is added and mixed.
After masking interfering niobium, Fe³⁺ is reduced. by sodium bisulfite, and subsequently, a mixture of hydrazin sulfate and ammonium molybdate is added to the solution and finally it is colored by heating on either a water bath or a hot plate.
The absorbance is measured at 825 mμ. The time required for the analysis is about 40 minutes.