Levent Pelit

ABSTRACT The preparation and characterization of a novel solid-phase microextraction fiber is reported with application to the determination of pesticides in fruit juice. The fiber was fabricated by electrochemically coating a stainless steel wire with a thin polymeric film of 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl) benzenamine. The procedure was initiated in 10 milliliters of acetonitrile containing 5.5 milligrams of monomer, 0.1 molar NaClO4, and 0.1 molar LiClO4 by cycling the potential between −0.5 and 1.2 volts with a scan rate of 100 millivolts per second. The morphology of the fiber surface was examined by scanning electron microscopy and its stability was characterized by thermal gravimetric analysis. The fiber was exposed to headspace extraction of bromopropylate, chlorpyrifos, lambda-cyhalothrin, penconazole and procymidone prior to the analysis by gas chromatography with an electron capture detector. Operational parameters affecting the extraction efficiency, adsorption and desorption times and temperature, and stirring rate were screened using a Plackett-Burmann Design. Emerging parameters were further optimized via Central Composite Design that were twenty minutes at 64 degree celsius for adsorption and 4.4 minutes at 250 degree celsius for desorption. Solution parameters were optimized to be 5.0 milliliters of sample in pH 2.0 Britton-Robinson buffer containing 0.1 milligram per liter NaCl to promote the volatilization of the analytes. The limits of detection were at the nanogram per milliliter level for the pesticides. The fiber was used as a selective and sensitive tool for the trace determination of these pesticides in grape juice.

ABSTRACT 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 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.