Determination of Zn2+ in Solid Pharmaceutical Dosage Forms by Means of Spectrophotometry in Micellar Media: Method Validation

In this study, a spectrophotometric method for the quantitative determination of zinc in a dietary supplement was validated. Zinc forms a ternary complex with Xylenol Orange and cetylpyridinium chloride in acetate buffer at pH = 5.5. The complex exhibits an absorption maximum at 560 nm. Linearity (range was 0.5–1.5 µg/mL, and correlation coefficient of the calibration curve was 0.9998), precision (repeatability variation coefficient and reproducibility variation coefficient were 1.57% and 1.77%, respectively), and accuracy (confidence interval of the mean recovery was 98.29–100.55%) of this method fulfil current pharmacopeial requests. Results obtained by spectrophotometric method were statistically compared with ones obtained by atomic absorption spectrometry and good agreement was found. The method can be applied routinely for quality control of solid pharmaceutical dosage forms containing zinc.