Analytical Sciences

Simple Regression Model Using an Optode for the Simultaneous Determination of Zinc and Cadmium Mixtures in Aqueous Samples

Bambang KUSWANDI,*  Andrew A. VAUGHAN,** and Ramaier NARAYANASWAMY**

*Department of Chemistry, University of Jember, Jember, Indonesia, 68121
**Department of Instrumentation and Analytical Science, UMIST, P. O. Box 88, Manchester, M60 1QD, UK

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).

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