[The determination of clonidine by charge-transfer-complex formation with iodine]

The donor clonidine (1) forms a charge-transfer-complex of stoichiometric composition 1:1 with the sigma-acceptor iodine. The association constant was determined by means of the Hildebrand-Beneshi equation being 38,000 l/mol. At first it forms an outer complex, characterized by charge-transfer band at 285 nm and the blue-shifted iodine band at 393 nm. From this complex the inner ionic complex results depending on time in which iodine iones arise reacting with unconnected iodine to triiodiones. These show absorptions at 291 and 364 nm. Resulting from it an assay of 1 worked out. The regression line is y = (4.370 +/- 0.256) x + (0.411 +/- 0.053), Srel = 1.3% (n = 10) and the linear range is placed between 0.01-0.25 mg/10 ml solution.