The paper discusses the electroreduction of Bi(III) ions in the aspect of expanding the ”cap – pair” effect. The ”cap – pair” rule is associated with the acceleration of the electrode’s processes by organic substances. The interpretation of the ”cap – pair” effect mechanism was expanded to include the effect of supporting electrolyte concentration on the acceleration process and the type of electrochemical active as well as used protonated organic substances. It has also been shown that the phenomena occurring at the electrode/solution interface can influence a change in the dynamics of the electrode’s process according to the ”cap – pair” rule.

Abstract. The simple and fast method for the determination of Bi(III) in non-complexing solution was proposed. The catalytic activity of cystine on Bi(III) ions electroreduction process were utilized. The calibration graph of Bi(III) in 4 mol·dm -3 chlorate (VII) in the presence of 1·10 -2 mol·dm -3 cystine is linear in the range of concentrations of Bi(III) from 7·10 -7 to 4·10 -5 mol·dm -3 . The detection and quantification limits were found to be 1.2·10 -7 mol·dm -3 and 4.02·10 -7 mol·dm -3 , respectively. Precision and recovery of the method were investigated by determination of Bi(III).