Simple, sensitive and accurate colorimetric methods have been developed for the determination of tizanidine HCl(I) and pancrunium bromide (II) in pure and in pharmaceutical formulations. These methods are based on the formation of an ion pair complex between the drug and BTB, BPB, BCP, and BCG at ph range from 3 – 4.5. The complexes are extracted into chloroform showing an absorption maximum at 410 nm. Beer`s law, Ringbom optimum concentration ranges, molar absorptivity, Sandell sensitivity were also calculated. The formed ion pair complexes into chloroform at ph 3.o and maximum absorbance at 410 nm. The stoichiometric ratio of the ion pair complexes was established to be 1:1 for all studied drug forms. The validity was assessed by applying the standard addityion techniques. The results were compared statistically with the official methods showing a good egreement with high precision and accuracy.

Egypt J. Pharm. Sci., 39, 463–474 (1998).