Controlled-potential back-titration with electrogenerated iodine as an intermediate: application to the determination of thiols.
A controlled-potential electroanalytical method has been devised for the accurate determination of small amounts of thiols. An adequate excess of iodine is generated, the sample is added and the unreacted iodine is then electrolytically reduced. The iodine consumed is calculated from the measured number of coulombs. Amounts of thiols in the range 0.2-5 mg may be determined with an error of +/- 0.05 %. A coulometric cell has been constructed which permits very high electrolysis rates, owing to efficient stirring by a large rotating platinum electrode combined with a high electrode-area to solution-volume ratio. A constant of 0.11 sec(-1) is found for the reduction of iodine. The necessity of careful control of background currents and current efficiency in coulometric determinations is discussed.
Torstensson
L G
LG
Department of Analytical Chemistry, Chemical Center, University of Lund, S-220 07 Lund 7, Sweden.