An alternative method for ethambutol (ETB) determination by UV spectrophotometry in pharmaceutical formulations using ETB complexation with Cu(II) was optimized employing a 3² full experimental design having Cu(II) and aqueous acetic acid/sodium acetate buffer at pH 4.6 as variables. The predominant complex stoichiometry in aqueous buffer solution at this pH and formation constant were obtained by using Job's method and Scatchard diagram, respectively. The complex crystalline structure of monocrystal was obtained by X-ray diffraction. The developed method was applied to the pharmaceutical formulation analysis being found: 408.0 ± 11.9 mg of ETB·2HCl, recovery range of 100.9-104.0% and detection and quantification limits of 0.8 and 2.8 mg L-1, respectively. The spectrophotometric method was compared to zone capillary electrophoresis and no significant difference was found within the 95% confidence interval
ethambutol; complexation; spectrophotometry; crystal structure
