The extent of quaternization can be monitored by determining the bromide ion concentration. When samples are dissolved in acetic acid, bromide ion is formed, the concentration of which depends on the degree of quaternization of the polyvinylpyridine. The electrogenerated iodine(I) forms a stable compound IBr with the bromide ion. It was established experimentally that electrophilic substitution by the iodine(I) on the pyridine ring does not occur
