Electrochemical fabrication of hydrophobic ionic liquid-polyaniline composite coating for solid-phase microextraction and its application in the GC determination of phenolic compounds

Abstract

A stainless steel wire was immersed in a hydrophobic ionic liquid (IL, i.e. 1-octyl-3-methylimidazolium hexafluorophosphate), then was heated under an infrared lighter to make the viscous IL form an even and reproducible film on the steel wire. After that polyaniline (PANI) was electrodeposited on it from an aqueous solution containing 0.1 mol • L-1 aniline and 1.0 mol• L-1 HNO3 through cyclic voltammetry. The potential range was -0.2~1.2 V (vs. saturated calomel electrode, SCE), the scan rate was 50 mV • s-1 and the cyclic potential scan was repeated for 70 times. For the electrodeposition a conventional three-electrode system was adopted, including the IL coated stainless steel wire as working electrode, a platinum wire as counter electrode and a saturated calomel electrode as reference electrode. The resulting PANI-IL composite coating was rinsed with methanol and distilled water. Following this, it was conditioned in a electric furnace with nitrogen atmosphere at 90°C for 30 min, at 250°C for 150 min. When the obtained fiber was cool, it was fixed on a home-made device for solid-phase microextraction (SPME) with epoxy resin. The coating showed netlike structure, with smaller hole and larger surface area than that of PANI. Taking several phenolic derivatives (i.e. 2-chlorophenol, 2-methylphenol, 2, 6-dimethylphenol, 2, 4-dimethylphenol and 3-methylphenol) as models, the analytical performance of the fiber was investigated. Under the optimized conditions (i.e. extraction temperature: 60°C; extraction time: 40 min; stirring rate: 600 r/min; NaCl concentration: 0.35 g • mL-1; desorption time: 3 min; desorption temperature: 250°C), when the phenols were determined by GC after headspace solid-phase microextraction with the fiber, the linear ranges were 0.048~400 μg • L-1 with correlation coefficients above 0.99; the detection limits were 6.1~98 ng • L-1 (S/N=3). The relative standard deviations (RSD) of chromatographic peak area were smaller than 5.5% for five successive measurements with single fiber, and the fiber to fiber RSD was 3.7%~12% for different phenols (n=3). The fiber also presented good stability and its extraction efficiency kept almost unchanged after being used for about 150 times; when the temperature was up to 300°C it did not decompose. In comparison with PANI fiber, the PANI-IL fiber showed higher extraction capability. The PANI-IL fiber was successfully applied to the determination of phenols in waste water from a chemical factory. © 2012 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.