く形波ポーラログラフ法でタンタル中のニオブを定量する場合の共存元素の干渉

抄録

For the square-wave(s.w.)polarographic determination of niobium in tantalum, was studied the influence of coexisting ions, such as Bi, Cr, Cu, Fe, Mo, Mn, Ni, Sb, Sn, Ti, V, W, Zr and Ta. A s.w. polarograph of Yanagimoto type PA-210 was used. The capillary characteristics (m^2/3t^1/6) and the drop time of DME were 2.17 mg^2/3s^-1/2 and 3.75 s, respectively, at-0.20 V vs. Hg-pool in concn. HCl. The analytical procedure is as follows. Dissolve less than 0.2 g Ta in 15 ml of 1:1 HF containing several drops of concn. HNO₃, 4 ml of 1:1 H₂SO₄, and 1 g of (NH₄)₂SO₄. Evaporate the solution on a hot plate until a syrup-like product is obtained, and heat 10 min more evolving the dense fume of SO₃. After cooling the syrup-like product, add 10 ml of concn. HCl to it. Dilute the solution with concn. HCl in a 25 ml volumetric flask, together with an appropriate quantity of coexisting ions of different concentration, while the solution contains (1.21 × 10^-4 4.0 × 10^-5) mol dm^-3 of Nb. The results found are summarized as follows. (A) Influence of the added Ta for the s.w. polarographic peak height of Nb is shown by the empirical formula;
h= 1.6071 × 10⁴ × 1.91 ^n-1 × (C_Nb/C_Ta) ^1.076…(1)
C_Ta=1.1× 10^-2×2^n-1…(2)
h: Peak height of Nb(mm), C_Ta: Concentration of Ta (mol dm^-3), C_Nb: Concentration of Nb (mol dm^-3) The concentration of Nb in the sample is determined from the peak heights by means of these equations. (B) The determination of Nb by this method was not interfered with 200 μg/g Ta of Mo, 100 μg/g Ta each of Bi·Fe and Zr, 20 μg/g Ta each of Cr·Sn and W, 10 μg/g Ta of Ti, 8 μg/g Ta of Ni, 4 μg/g Ta of V, 2 μg/g Ta of Mn, or 1 μg/g Ta of Sb, but was interfered with 1μg/g Ta of Cu. (C) The concentration range of the determination of Nb by this method was 1.7 × 10^-5 mol dm^-3 to 1.3 × 10^-4 mol dm^-3. The lower limit of the detection of Nb by a standard addition technique was 3.2 × 10^-6 mol dm^-3.