Feasibility of performing multiple
coulometric titrations in a single course of electrolysis is presented.
In these titrations, three pairs of cathode and anode compartments
were connected with a network of electrodes and salt bridges. Passage
of current through the cell caused concurrent electrolysis in cathode
and anode compartments. Electrogenerated reagents produced in these
compartments were used as titrants for quantifying the analyte samples.
Endpoints of the titrations were determined from the visual color
change of an indicator. The charge passing through the cell was monitored
and Faraday’s laws of electrolysis were applied to assess the
quantitative relation between the charge and analyte concentration.
Experimentally determined coulombs required to titrate aqueous potassium
hydrogen phthalate, MnO
4
–
, OH
–
, and S
2
O
3
2–
were 0.100,
0.466, 0.103, and 0.0934 C, respectively. These results matched with
estimated values of 0.0965, 0.482, 0.0965, and 0.0965 C, respectively.
Agreement between the coulombs determined from experimental results
and reaction stoichiometry suggests a feasible application of concurrent
coulometric titrations. Efficacy of the method was tested for determining
the active ingredients in household vinegar and vitamin C dietary
supplement tablets. Quantities of acetic acid and ascorbic acid in
these products were 5.1% and 980 mg, respectively, agreeing with the
quantities determined from volumetric titrations (5.1% and 990 mg)
and manufacturer’s label (5.0% and 1000 mg).