Determination of chromium(VI) by differential-pulse polarography with a sodium fluoride supporting electrolyte

Abstract

The polarographic determination of Cr(VI) is usually performed in a sodium hydroxide, ammonium tartrate or ammonium acetate supporting electrolyte. This study suggests that 0.2 M sodium fluoride solution is a superior medium for trace level determinations. With differential-pulse polarography, the sensitivity in this medium is 0.64 nA (nmol l^–1)^–1 Cr(VI) at the 10^–8M level, and the detection limit is 1.6 × 10^–8M Cr(VI). With 1 × 10^–7M Cr(VI), 10-fold excesses of Fe(III), Cl^– and NO₃^– do not change the current by more than 4%; Cu(II) causes an 8% decrease. The presence of Fe(III), Cu(II) and Cl^– causes significant error with ammonium acetate and ammonium tartrate electrolytes.