Simple regression model using an optode for the simultaneous determination of zinc and cadmium mixtures in aqueous samples

An optical-fiber chemical sensor (optode) is described for the simultaneous determination of Zn2+ and Cd2+ mixtures using 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol immobilized onto XAD-4 (Br-PADAP/XAD-4). A simultaneous analysis was achieved by using a single-wavelength kinetic approach coupled with a regression model. Here, the regression model was derived for the slope response of Br-PADAP/XAD-4 to binary mixtures of the metal ions, Zn2+ and Cd2+, at pH 8. The model was used then to predict the concentration of one metal ion while the other was kept constant. This was found to be reasonably successful for Zn2+ and Cd2+, with deviations of 3% and 10%, respectively. The sensor was also found to provide excellent sensitivity for both metal ions with excellent LODs (< 0.1 ppm) and very short analysis times (< 30 s).