Indirect method of the biosensor based on flow injection analysis for determination of mercury

In this research a biosensor based on flow injection analysis (FIA) for indirect determination of mercury (Hg (III)) by enzymatic inhibition has been developed. Glucose oxidase in Nafion solution immobilized on a screen-printed carbon electrode (GOx/SPCE) bulk modified with manganese dioxide 5% (m) as a working electrode (Gox/MnO2/SPCE) assembled with an electrochemical cell as a detector based on FIA was experimentally studied.
The optimum conditions of the biosensor based on FIA, an operating potential of +0.46 V versus Ag/AgCl, supporting electrolyte of 0.1 mol.L-1 phosphate buffer solution at pH 7.0, enzyme loading of 80 U.cm-2, glucose loading of 200 mg.L-1 with 250 L injection volume and flow rate 1.2 mL.min-1, were continually studied.
The accuracy of the biosensor responded to mercury was evaluated in terms of a linear range of 100-1000 g.L-1 with the linear equation of y=0.0407x-0.5760 and r2=0.9975. The limit of detection and limit of quantification were of 29 g.L-1 and 96 g.L-1, respectively. The repeatability and reproducibility were of 3.68% (10 measurements) and 4.12% (3 sensors), respectively. After inhibition, the biosensor surface was regenerated by flowing through 0.05 mol.L-1 EDTA for 2 min and percentage of regeneration was at 100%. The storage stability of the biosensor had been investigated after the electrodes were stored in dry condition at 4 C in a refrigerator and its stability yielded more than 21 days with relative current percentage of 62%.
Moreover, interferences of an inhibition-based enzyme catalytic process were investigated; the results presented only Pb(II), Cd(II) and Cu(II) having a significant effect at high concentration of 10 mg.L-1 but no effect at low concentration of 1 mg.L-1
Furthermore, the kinetic catalytic reaction of GOx was studied. The apparent Michaelis-Menten (Km) constant and Imax could be calculated to be 5.80 mmol.L-1 and 4.41 A, respectively. The immobilized glucose oxidase indicated acts as the free enzyme. Besides, the kinetic inhibition of GOx was investigated. The result was found and concluded that GOx was inhibited by mercury as a noncompetitive inhibition type.
The biosensor based FIA was evaluated to detect mercury in certified reference material (DORM-2) with certified values of 4.640.26 mg.Kg-1 mercury. As the results, the proposed biosensor presented mercury at 4.550.07 mg.Kg-1 with good recovery of 98%.
Moreover, the practical biosensor was successfully demonstrated in determination of mercury in real samples, and the samples were detected by cold vapor generation atomic absorption spectrometry as the reference method. The results from both methods were calculated using paired t-test. The t-value is significantly smaller than the tabulates critical value indicating that it is not significant statistical different between these results at a confidence interval for 95% probability.