Spectrophotometric Estimation of Bismuth 465nm or at UV region 337nm

Estimation of Bismuth

Introduction:

Iodide Complxes:

The iodine Complxes   of Bismuth (III) are orange colored, and Beers law is obeyed in the presence of an excess of I- ions (concentration of potassium iodide greater than   1%)

The complex is soluble in alcohols, esters, and ketones.

Sensitivity:

The molar coefficient ε ~ 34,000 at 337 nm in water

The coloration is stable for three to four hrs. The acidity should be fixed between the limit 1-2 N H2SO4

Interfering ions:

Oxidizing agents liberate iodine and should be reduced with e.g.: Sulpurous acid. CuI and AgI can be separated by precipitation without Loss of Bi (III), but PbI2 retains Bi (3) and interferences. Large amounts of   Cd (II) consume (2) I- by the formation of complexes .Hg (II) does so to an even greater extent .1000ppm of iron, 100 ppm of pb (II), 20 ppm of Cu (II) and 400 ppm of As, F-. and tartarate ions do not interfere

Pt (IV), Pd (II), Sn (IV) and Sb (III) produce interfering colors, but Sb (III) only interferes above 200 ppm, and the same doubtless applies to Sn (IV) .Sb (III) and Bi (III) can be estimated simultaneously, Cl- and F- weaken the coloration

REAGENTS:

Potassium iodide, 10% in water;

Sulphurous Acid solution, 5% freshly prepared;

Hypo phosphorous acid, 30% in water

Operating Procedure:

The initial solution consists of 10-20ml, containing from 5-50μg of bismuth (III). The acidity should be adjusted to 1-2N H2SO4. Then .0.1ml

Of sulphurous acid, 1ml of hypo phosphorous acid, and 3ml of iodide are added and the volume made up to 25ml. Colorimetry is performed at 465nm, or alternatively in the UV at 337nm

The blank test or the calibration curve should be determined under identical conditions with respect to acidity and the concentration of salts and iodine