Electrophoretic rapid separation and quantitative determination of Hg(II), Pb(II), Cd(II), Cu(II) and Bi(III)

Abstract

Hg²⁺, Pb²⁺, Cd²⁺, Cu²⁺ and Bi³⁺, i.e., hazardous heavy metal ions, were rapidly separated from each other by electrophoresis and determined quantitatively by colorimetry.
The suitable condition for the electrophoretic separation was found by analyzing pH-migration mobility curves (Figs. 1, 2, 3) obtained by the multicell-electrophoresis.
Cellulose acetate(2 cm×11 cm strips) and “Cellogel” (2.5 cm×15 cm strips) were used as supporting material.
As electrolyte, sodium citrate, lactic acid and α-hydroxyisobutyric acid (α-HIBA), each at 0.1M, were examined, and pH was adjusted to 18 with 0.1 M HCl and 0.1 M NaOH.
At 4 cm from the strip-end(anodic side) 0.5 μl of sample solution(2 mg/ml) was spotted.
The migration rates(shown in Figs. 1, 2, 3) in each solution at different values of pH on the cellulose acetate strip were obtained by applying the electric field of 300 V/11 cm for 5 min. Good separation was obtained in 0.1 M α-HIBA solution of pH 2.3 as shown in Fig 3.
For the concentrations of α-HIBA ranging from 0.2 M to 1.0 M, the higher the concentration the less was the migration mobility, and the narrower and clearer were the electrophoretic spots except for the solutions of 0.8 and 1.0 M, since in such solutions the suporting material, cellulose acetate, shrunk by being electrically heated too much. In the solutions more dilute than 0.2 M the separated spots became not clear due to the diffusion. Therefore, 0.4 M α-HIBA solution (pH 2.2) was used.
For quantitative determination, “Cellogel” was used as supporting material, instead of cellulose acetate, because of its pure quality and little affinity to the samples.
One microliter of a mixture of the five metal ions was spotted at 1.5 cm from the strip-end (anodic side). Migration was carried out for 10 min under the electric field of 800 V/15 cm.
As developing color reagents, 0.01 g/100 ml dithizonecarbontetrachloride and ammonium vapour were used, and after being dried the metal-ionogram was cut into five strip pieces. Ten milliliter of 10 g/100 ml NaOH solution was added to the Cd strip, and 10 ml of 10 g/100 ml ammonium citrate solution of pH 10 to the strips of Pb, Bi or Hg, respectively. Two milliliter of 10 g/100 ml ammonium citrate solution of pH 10 and 10 ml of water was added to the Cu strip. Each strip was shaken with the solution for 10 min. The pH of each solution was adjusted before the extraction by adding hydrochloric acid (1 : 1); for Pb and Cu to pH 9, for Hg to pH 4.8 (solutions of Cd and Bi were left unadjusted).
The metals were extracted from the solution with dithizone-carbontetrachloride, except copper, which was extracted with sodium diethyldithiocarbamate-carbontetrachloride. The absorbances of the organic phases were measured at 518 nm for Cd and Pb, at 436 nm for Cu, and at 490 nm for Bi and Hg.
The experimental error was within 5%. The minimum limits of determination were 0.5 μg for Bi, 1.0 μg for Cd and Hg, while 1.5 μg for Pb and Cu.