Cobalt and copper hexacyanoferrate modified carbon fiber microelectrode asan all-solid potentiometric microsensor for hydrazine

This article reports on the novel mixed cobalt and copper hexacyanoferrate (CoCuHCF)-modified carbon fiber cylinder microelectrode (CFCME) and its- ap plication to potentiometric determination of highly toxic hydrazine. The su bstrate CFCMEs were fabricated in a standard manner using carbon fibers of 7 mu m in diameter The CoCuHCF film was deposited electrochemically by cycl ing the potential between 0 and + 1.0 V (vs. Ag/AgCl) in a solution contain ing the precursor salts. It exhibited good chemical stability in the pH ran ge from 1 to 9. The effects of the coverage/thickness of the CoCuHCF coatin g, of the pH of a measurement solution, and of the activation of the sensor , on the potentiometric response to hydrazine were examined in detail. The potentiometric behavior of CoCuHCF film in the presence of hydrazine. with the potential (emf) slope of - 55mV/decade, was compared with those of four single metal HCF films (CoHCF, CuHCF FeHCF, and NiHCF) prepared in the sam e way, and the possible role of the CoCuHCF film components is explored and discussed. The emf versus log C-Hyd calibration plot was linear over 3 ord ers of magnitude, from 1.0 x 10 (- 6) to 1.0 x 10 (- 3) mol/L, with a corre lation coefficient of 0.995. The limit of detection was found to be 5 x 10 mol/L. The response times of 10 to 30 s and the temperature coefficients of ca -2.7 mV/degrees C were obtained at various hydrazine concentrations. Th e repeatability of measurements was very good with the relative standard de viation ranging from 3 to 4 % (n = 10), depending on hydrazine concentratio n. The selectivity of the reported microsensor was found excellent, except in the case of a feu negatively charged interferents for which it was great ely improved by an additional Nafion coating. The useful lifetime of the al l-solid microsensor was found to be more than 2 months when stored in air.