Electrocatalytic reduction of nitrite at a carbon fiber microelectrode chemically modified by palladium(II)-substituted Dawson type heptadecatungstodiphosphate

A new type of chemically modified electrode (CME) was fabricated by electro deposition of palladium(II)-substituted Dawson type heptadecatungstodiphosp hate, K-8[P2W17O61Pd(H2O)] (abbreviated as P2W17Pd in the following), onto a carbon fiber microelectrode (CFME). A pair of waves was observed on the P 2W17Pd CFME, which is ascribed to the redox process of the palladium center in the heteropolytungstate. After continuous potential scanning for 30 min in a pH 4.0 buffer, 92% of the original electrode response remained for th e P2W17Pd CFME. The P2W17Pd CFME had high electrocatalytic activity for nit rite reduction and exhibited good reproducibility and stability. The cataly tic peak current was found to be linear with the nitrite concentration in t he range of 1.0 x 10(-7) similar to 1.2 x 10(-3) mol l(-1) (at 25 degrees C ) with a correlation coefficient of 0.9886 The detection limit (signal/nois e = 3) was found to be 2.0 x 10(-8) mol l(-1). The response time of the mic rosensor for nitrite measurement was less than 15 s. For 10 parallel measur ements of 1.0 x 10(-5) mol l(-1) nitrite, the relative standard deviation ( RSD) was found to be 4.5%. The sensitivity of the microsensor was 0.57 nA ( mu mol l(-1))(-1). The P2W17Pd CME was applied successfully as an electroch emical detector (ECD) to determine the nitrite level in rat brain by flow i njection analysis (FIA) coupled with microdialysis sampling. The linear ran ge was over three orders of magnitude and the detection limit was 3.0 pmol for nitrite determination. The mechanism of the catalytic reaction was also addressed. (C) 1999 Elsevier Science S.A. All rights reserved.