Glassy carbon electrode modified with hybrid films containing inorganic molybdate anions trapped in organic matrices of chitosan and ionic liquid for the amperometric sensing of phosphate at neutral pH

This work reports an amperometric method for phosphate analysis based on the use of a surface modified glassy carbon electrode (GC). In one configuration of the electrode the surface is modified with ammonium heptamolybdate incorporated in chitosan matrix. A second configuration of the surface modified electrode is formed by introducing, on top of the chitosan film, an additional layer of molybdate dissolved in ionic liquid, 1-Ethyl-3-methylimidazolium tetrafluroborate. The molybdate layers are then coated with a film of PSS + PEDOT (Poly stryrenesulphonate + Poly (3,4-ethylene dioxythiophene)). The chitosan matrix provides the acidic conditions required for the surface molybdate to react with phosphate forming electoactive phosphomolybdate which allows amperometric determination of phosphate. The reduction of ammonium phopshomolybdate is monitored at -0.140 V vs. NCE (Hg/Hg2Cl2/1 N KCI) at pH 7.2 in Tris buffer. The linear range of detection for phosphate lies between 19 and 100 p,M with the first configuration electrode. The limit of determination could be extended to a lower range of 0 .79-32 mu M using the second configuration electrode. This method is found to be free from interference from anions like arsenate, nitrate and chloride. The method is validated by determining phosphate concentration in a commercial fertilizer sample. This method is highly selective, sensitive, enzyme less and requires no other additional reagents. Additionally it works at neutral pH, hence would be applicable for phosphate analysis in biological samples. Unlike ICP-OES analysis which requires highly sophisticated and costly instrumentation, the proposed method involves simple and cheaper instrumentation requirements and is suitable for field measurements. (C) 2011 Elsevier B.V. All rights reserved.