SPECTROPHOTOMETRIC-COMPLEXOMETRIC TITRATIONS(Ⅰ)——THE TITRATION OF MICRO-QUANTITIES OF IRON(Ⅲ)
Chen Yongzhao, Chen Huanguang
1982, 3(3):
319-326.
Asbtract
(
)
PDF (556KB)
(
)
Related Articles |
Metrics
The stability constant of Fe(III)-EDTAcomplex is rather large (logK = 25.1). Iron should be titrated at as low as pH 1, but owing to no suitable indicator to give a sharp end point, it has to be titrated at pH 2-3, which minimizes the selectivity of the titration. Through the comparison of the absorption curves of Bi-xylenol orange complex at different pHvalues, we found that at a wave length of 540 nm and at pH 0,8, the end point of the spectrophotometric titration of bismuth still was very clear. So we chose bismuth nitrate as the back titrant in the back titration of iron at a much lower pHvalue.This paper reports the optimum conditions for the spectrophotometric titration of 3-100Mg of iron in about 30 ml volume. The selectivity of this method is very high. 1 to 2 mg of Al, Ti(IV), Cr(III), Cu, Pb, Zn, Mn, La, Ce(III), W(VI), Mo(VI), V(Y), As(I), Mg, Ca and Ag, and 100ug of Hg, Sb(III), Ni and Th, as well as large amounts of chloride, fluoride and phosphate anions do not interfere. Using ammonium fluoride as a masking agent, 10 mg of Al, 200 ,ug of Zr and 100 Mg of Sn(IV) can be tolerated. Sodium sulfate can mask thorium up to 500 Mg. Co(II) is the only cation that interferes, and in the presence of EDTAit is easily oxidized to Co(III), which is cotitrated with iron.Micro-quantities of iron in quartz, tap water, aluminium alloys and pure aluminium, without preliminary separation, can be successfully and accurately determined with this method.
