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A novel polymer-clay composite solid phase microextraction fiber is reported for the adsorption of methanol in biodiesel with subsequent determination by gas chromatography coupled with a flame ionization detector. The fiber was fabricated using a stainless steel wire that was subjected to electropolymerization in 0.1 molar NaClO4 containing thiophene and montmorillonite clay dispersed in acetonitrile. Electrochemical deposition was maintained by cycling the potential from 0.2 to 2.2 volts at a scan rate of 50 millivolts per second. Examination of the surface by scanning electron microscopy revealed that the fiber had a porous surface suitable for the adsorption of volatile analytes. The properties of the fiber were investigated by Downloaded by [New York University] at 10:12 29 May 20152 thermogravimetric analysis and infrared spectroscopy that showed that the clay was inserted in the structure. The fiber was exposed to methanol in biodiesel. The adsorption time, adsorption temperature, and desorption temperature were optimized. Under the optimized conditions, the linear dynamic range for methanol extended from 0.029 to 0.24 percent (m/m) with a limit of detection of 0.009 percent (m/m). The method was employed for the analysis of biodiesel and the results were validated with a standard EN 14110 method.