Method development for determination of Iodide ion in egg using electrochemical techniques

Abstract

The electrochemical detection with flow injection (FI) system was developed for the determination of iodide ion in egg samples. The oxidation potential of iodide was investigated using cyclic voltammetry (CV) in 60mM phosphate buffer (pH 5). The experiments were compared between using boron-doped diamond (BDD) and using glassy carbon electrodes (GC). It was found that both electrodes provided well-defined cyclic voltammograms. However, the background current of BDD electrode was much lower than the background current of GC electrode. The BDD electrode was selected as working electrode for this work. The pulsed potential waveform was also studied and applied with flow injection amperometric detection in order to improve the stability of the signal that might affected by the adsorption of electrochemical species at the electrode surface. The optimized pulsed potential waveform parameters were 0.8 V detection potential; 30 msec delay time; 30 msec integration time; 1.2 V oxidation potential; 700 msec oxidation time; 1.1 V reduction potential; and 30 msec reduction time. The FI-PAD-BDD was carried out in 60 mM phosphate buffer pH 5 at flow rate of 1 ml/min. The method was evaluated with standard iodide. The linear dynamic range was 50 to 2000 mug/L. The limit of detection and the limit of quantitation were 5.4 mug/L and 16.5 mug/L, respectively. The recovery was 114% with 6% RSD. The method was intended to apply for determination of iodide in egg sample after alkali dry ashing; however, there was a problem with the incompatibility of the matrix to the electrochemical system. Alternatively, microdialysis sampling was attempted in order to retrieve iodide ion from egg samples. The preliminary results of iodide in egg samples obtained from both microdialysis with FI-PAD-BDD method (1.06 mug/g of egg with 6% RSD) and alkali dry ashing with catalytic colorimetric method (1.11 mug/g of egg with 0.1% RSD) were comparable.