Normal and differential demasking flow-injection manifold for the direct spectrophotometric determination of zinc(II) in biological materials and pharmaceutical formulations

A normal and a differential demasking flow-injection (FI) manifold were dev eloped and optimized for the spectrophotometric determination of microamoun ts of Zn(ii) in biological materials and pharmaceutical formulations. The r eported method is very sensitive, rapid, simple and it is based upon the re action of Zn(ii) with 2,2'-dipyridyl-2-pyridylhydrazone (DPPH) in a strongl y basic medium to form a yellow-coloured complex (lambda (max) = 448 nm). B y using the differential demasking manifold, the tolerance of the method to many cations was enhanced by a mean factor of 25. The obtained calibration graphs were linear in the range of 0-10 mg l(-1) Zn(II), at a sampling rat e of 120 injections h(-1) in both cases. The precisions of both manifolds w ere very good (RSD = 0.6 and 0.8%, respectively) and the 3 sigma detection limits were quite satisfactory (c(L) = 4 and 6 ng ml(-1) respectively). The method has been successfully applied to the determination of Zn(ii) in ser um, human hair and pharmaceutical formulations with recoveries ranging betw een 98.0 and 101.6%. The obtained results were also in excellent agreement with flame atomic absorption spectrometry (FAAS), since the mean relative e rror was e(r) = 0.9%.