Sensitive assay procedure for ethambutol hydrochloride via charge transfer complex formation

The charge transfer complex formation between ethambutol and iodine was investigated and utilized as the basis for a sensitive spectrophotometric procedure for ethambutol and its dosage forms. The solutions exhibited blue-shifted iodine bands at 293 and 360 nm. A Job's plot of corrected absorbance against the mole ratio of ethambutol to iodine indicated a 1:2 drug-iodine ratio. At 293 nm, the absorbance was linear (r=0.9998) over the 0.25-15-microgram/ml concentration range, but the concentration range for best accuracy is 1.6-5.8 microgram/ml. The method can be applied successfully to the analysis of commercially available ethambutol tablets.