Schiff bis bases: analytical reagents. II. Spectrophotometric determination of manganese from pharmaceutical forms.

By condensing ethyl-o-hydroxybenzene with ethylene diamine, and 1-ethyl-salicylidene bis ethylene diamine, a Salen-type Schiff bis base is obtained. These Schiff bis bases present a good capacity of complexing the Mn(II) ions, resulting brown complexes. In this paper, the results of a study concerning the use of the Schiff bis base as reagent in spectrophotometric determination of the Mn(II) is presented. The above mentioned Schiff bis base forms a brown complex with Mn(II) cation, with maximum absorbance at 460 nm, and molar absorbtivity (epsilon)=9.8 x 10(4). The complex with Mn(II) presents a maximum stability at pH 6.0. The combination ratio was established by isomolar series method, and it is 1:2 (metal:ligand). The calculated apparent stability constant is beta(n)=2.943 x 10(-5). The absorbance is proportional to Mn(II) concentration in the range of 10-70 microg ml(-1). In this range, the Lambert-Beer law is respected, the linearity coefficient being 0.9989, S.D.=0.83, R.S.D.=0.88 (n=7). In these conditions, the complexation reaction of Mn(II) is interfered by other cations, Fe(II); Fe(III); Ni(II). The results obtained for spectrophotometric determination of Mn(II) using this Schiff base as reagent were successfully applied to pharmaceutical products containing Mn(II) cation.