The multi-wall carbon nanotubes were used as an immobilization matrix to incorporate thionin as electron transfer mediator onto a glassy carbon electrode surface. Due to unique electronic properties of MWCNTs and electrocatalytic activity of thionin, the combination of thionin and MWCNTs results in a remarkable synergistic augmentation on the response. A chemically modified electrode prepared by adsorption of thioinin on CNT shows excellent catalytic activity for reduction iodate, periodate and nitrite in acidic buffer solutions at unusual positive and it can be used as stable and sensitive sensor for these analytes. The results indicated that the modified electrode exhibited efficiently electrocatalytic reduction for iodate, periodate and nitrite in acidic buffer solutions at unusual positive potential. Nitrite, iodate and periodate were determined amperomerically on rotated modified electrode in pH 2. Under optimized condition in amperometry method the concentration calibration range, detection limit and sensitivity were about, 1m M -10mM, 0.4m M and 12.44 nA/m M for periodate, 2.0m M -10 mM, 1m M and 5.36 nA/m M for iodate and 6 m M-15 mM, m M and 2 nA/m M for nitrite. The catalytic rate constants for oxoanions reduction were determined by cyclic voltammetry method based on the Laviron theory, they were about 1.34 ×104 , 1.68 ×104 and 4.93 ×103 M-1 s-1 , for iodate, periodate and nitrite, respectively. The resultant thionin / MWCNTs modified glassy carbon electrodes exhibit high catalytic activity, fast response time ( within 5 s) to above anions reduction, excellent stability, long term life and good reproducibility. This sensor indicate great promise as an amperometry detector for analysis of nitrite, iodate and periodate in chromatographic or flow systems.
