The chromatomembrane method used for sample preparations in the spectrophotometric determination of zinc and copper in pharmaceuticals

The chromatomembrane cell (CMC) was used to extract zinc and copper and to preconcentrate them for their separation from pharmaceutical preparations. The method performance was evaluated at the determination of the enrichment factor, the linearity of response, the reproducibility, the accuracy and the sensitivity. In practice a five-fold enrichment has been enough provided that sample sizes of 0.825 ml were introduced. Good linearities for zinc and copper (r² > 0.99) were observed under this condition. The relative standard deviation (<3%) proved the good reproducibility of the method. The accuracy has been verified using model solutions, which were prepared from a certified reference. Recoveries of 98.8, 99.5 and 100.3% were achieved with solutions containing 0.1, 0.3 and 0.5 μg ml^-1 Zn(II), respectively. In case of copper 101.2, 99.6 and 100.6% recovery were obtained for 0.1, 0.4 and 0.7 μg ml^-1 Cu(II), respectively. The detection limits (three-fold of the signal-to-noise ratio) were estimated at 0.04 μg ml^-1 for both. The proposed method was applied on pharmaceutical preparations and the results were found to be in a good agreement with the contents guaranteed by the producers.