Coprecipitation and X-ray fluorescence determination of bismuth in copper and silver metals

Abstract

Bismuth (<100μg) was coprecipitated with iron(III) hydroxide (100μg as iron) from 20 to 500ml of aqueous solutions in the pH range of 811. As the X-ray intensity of bismuth decreased gradually with aging of the precipitate, filtration should be made immediately after precipitation. A linear calibration curve was obtained over (1100)μg of bismuth. The coefficient of variation was 1.8% with 10μg of bismuth in five runs. Sensitivity was 20 (counts/s)/μg Bi. The following amounts of foreign ions were tolerated in the determination of 100μg of bismuth:Zn and Cd 1g, Ni 250mg, Co 25mg, Se(IV) 2mg, Mn(II) and Sn(IV) 200μg, As(III) 100μg, P(V)and Cr(III) 50μg, Pb(II) 25μg. The procedure is as follows: Dissolve 2g of copper or silver in 20ml of 6.5M nitric acid. Add 100μg of iron(III), adjust pH to 910 with aqueous ammonia, and collect the precipitate on a membrane filter (25mm, 0.3μm). Wash the precipitate with a dilute solution of ammonia (pH9). Measure the intensity of BiLα line (2θ=33.0°) and that of background (2θ=32.6°), respectively, in a vacuum for 40s by using a molybdenum-target tube (50kV, 20mA), a LiF (200)crystal and a scintillation counter.