Amperometric detection of periodate using a graphite electrode modified with a novel alpha-Keggin-type silicotungstic acid salt and determination of ethylene glycol in antifreeze fluids

A novel, water-insoluble, salt of alpha -Keggin-type silicotungstic heterop olyacid with hexadecylpyridinium cation (SiW(12)Hex) was synthesized. The s alt was immobilized onto the surface of spectroscopic graphite electrodes t hrough physical adsorption from acetone solution to produce chemically modi fied electrodes (SiW(12)Hex-CMEs). Some preliminary electrochemical data of soluble silicotungstate salts as well as of the modified electrode are giv en. Parameters such as the roughness of the electrode surface, the surface coverage and pH effect were investigated. The modified electrode was employ ed for the amperometric detection of periodate through its electrocatalytic reduction to iodate at -0.40V (vs. Ag-/AgCl) at pH 4.5 and for the indirec t determination of ethylene glycol in antifreezing fluids. Linear plots of cathodic current versus the ethylene glycol concentration in the range of 0 .2-5 mM ethylene glycol were obtained. An accuracy better than 2.1% and a r eproducibility (relative standard deviation) of 1.9% (n = 10) for a 5 x 10( -4) M standard solution of ethylene glycol were achieved. The recovery was 98-101 %.