Determination of small amounts of phosphorus(V) oxide in flat glass

Abstract

We studied the factors which affect the reproducibility of the resul~s of the determination of P20~ in relation to the yellow phosphovanadomolybdate complex: the size of the portion, the aliquot, and acidity of the solutions. The studies were carried out on flat glass with a known concentration of P205 (0.35%). The optimal conditions for the formation of the yellow phosphovanadomolybdate complex were found experimentally. The determination of P~05 was carried out in a I N solution of nitric acid in a cell where the length of the working layer was 20 mm and ~ = 450 nm (dark-blue filter). The recommended sizes of ~he portion as a function of the proposed concentration of P~Os are given below: Concentration of P205 Mass of portion in the glass, % of glass, g 0.2-0.4 0.5 0.5-0.6 0.3 0.7-1.0 0.2 Construction of Calibration Graph. In order to allow for the possibly disturbing effect of all the components of the glass, a standard specimen (GSO-3425-86) of a flat glass composition which did not contain P20s was used to construct the calibration graph. Into eight Pt beakers we weighed out 0.5 g each of the GS0-3425-86 flat glass which was decomposed using a mixture of 3 ml nitric acid and I0 ml HF acids; the contents of the beakers were then evaporated to dryness. The dry salt residue was dissolved by heating in 3 ml of nitric acid, 30 ml of water was then added, and the contents of the beaker transferred to a 100-ml measuring flask (in this case the volume of liquid in the flask must be ! 50 ml). Then into seven flasks we poured, respectively, 2, 4, 6, 8, I0, 12, and 14 ml of the standard solution containing 0.2 mg/ml of P205. The solution in the eighth flask was the control. We poured 20 ml of the vanadate--molybdate reagent into each of the eight flasks, water was added up to the mark, and the contents carefully stirred. In this case ~he acidity of the medium was made ~i N by nitric acid. After 30 min we measured the optical density of the solutions in a photoelectric colorimeter at ~ = 450 nm (dark-blue filter) using a cell in which the length of the working layer was 20 mm, From the data obtained we constructed the calibration graphs plotting the concentration of P~Os in mg/100 ml of solution along the abscissa while along the ordinate we plotted the corresponding values of the optical density. Preparation of the Vanadate--Molybdate Reasent. Solution I: 1.5 g of ammonium vanadate was dissolved with heating in 250 ml-of water; a few drops of a concentrated ammonia solution was added to remove the color of the solution; the solution was filtered and 250 ml of nitric acid solution, dilution 2:3, added. Solution II: 40 g of ammonium molybdate was dissolved with heating in 400 ml of water; the solution was filtered and a further I00 ml of water added. The vanadate-molybdate reagent was made immediately before us~ by mixing with vigorous stirring 50 g each of solutions I and II and adding 9 ml of concentrated nitric acid. *Here and elsewhere concentration by mass is given.