A normal and a differential demasking flow-injection (FI)
manifold were developed and optimized for the spectrophotometric
determination of microamounts of Zn(II) in biological materials
and pharmaceutical formulations. The reported method is very sensitive,
rapid, simple and it is based upon the reaction of Zn(II) with
2,2′-dipyridyl-2-pyridylhydrazone (DPPH) in a strongly basic medium
to form a yellow-coloured complex (λmax = 448
nm). By 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 rate of 120
injections h−1 in both cases. The precisions of both
manifolds were very good (RSD = 0.6 and 0.8%, respectively) and the
3σ detection limits were quite satisfactory
(cL = 4 and 6 ng ml−1 respectively).
The method has been successfully applied to the determination of
Zn(II) in serum, human hair and pharmaceutical formulations with
recoveries ranging between 98.0 and 101.6%. The obtained results were also
in excellent agreement with flame atomic absorption spectrometry (FAAS),
since the mean relative error was er = 0.9%.
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