Development of a sol–gel optical sensor for analysis of zinc in pharmaceuticals

Abstract

A Zn(II) optical sensor was developed by incorporating 4-(2-pyridylazo)resorcinol (PAR) in a sol–gel thin film. Acid- and base-catalyzed methods to prepare the sol–gel layers have been studied, as well as different types of precursors and different PAR concentrations. Sensors based on co-polymerization of tetraethoxysilane (TEOS) with 3-amynopropyltriethoxysilane (3-APTES), basic catalysis, water:alkoxyde ratio of 4 and PAR concentration of 1.0gl−1 showed optimum performance in the proposed working conditions. The sensor was coupled to a multicommutated flow system and applied to the direct determination of Zn(II) in injectable insulins. Optical transduction was based on the use of a dual-color LED and a photodiode. The sensor showed optimum response at pH 5.5 with maximum absorbance at 500nm. Its regeneration was accomplished with a solution of KSCN acidified to pH 3.0 with HCl. Linear response was obtained for Zn(II) concentration range of 5.0–25.0μgl−1, with detection limit of 2.0μgl−1 and sampling frequency of 16 samplesh−1. Interference from foreign ions was studied at 10:1 (w/w) ratio added ion:Zn. The results obtained on real samples analyzed were in good agreement with those obtained by a standard method, with relative deviation errors inferior to 1.2%.