| The ionic liquid has not detectable vapor pressure under normal conditions and was called as"green solvent", it may replace traditional organic medium for solvent extraction. However, present ionic liquids lack good hydrophobic property and is easy to stick on wall of the bulk during extraction process. In order to overcome the difficulty, we designed and synthesized a new temperature-controlled ionic liquid 1-isooctyl-3-methylimidazolium hexafluorophosphate.The modified two-steps method using non-solvent and temperature programmed technologies was developed for synthesis of ionic liquids1-isooctyl-3-methylimidazolium hexafluorophosphate. After the crude products were diluted by acetone, it was decolored with activated carbon and almost colorless ionic liquids were obtained. There is no obvious absorption peak in the wavelength range of 400-800nm. Moreover, the results of the IR and 1H-NMR analysis confirmed the structure of the ionic liquid.The physical and chemical properties of the ionic liquid such as thermal stability and solubility were investigated in detail. It can be seen from the results of Differential Scanning Calorimetry and Thermo gravimetry analysis that its melting point is about to 52.6℃and the initial decomposition temperature is at 373℃, this indicated the ionic liquid remain a liquid state under temperature between 52.6℃and 350℃. Before reaching the decomposition temperature, no obvious loss of weight was observed. The ionic liquid is easy to dissolve in acetone, methanol and acetonitrile and difficult to dissolve in water, toluene and carbon tetrachloride. Moreover, a new spectrophotometry was developed and applied to measure solubility of ionic liquids in water based on the absorbance of imidazole cation at 210nm linearly increasing with the concentration of the ionic liquid in water. It was found the solubility of 1-isooctyl-3-methylimidazolium hexafluorophosphate is 2.897 mg/mL.A 250ml of the solution containing 10μg of standard pesticide (dicofol, deltamethrin, cypermethrin and fenvalerate) was used for study on the effect of various factors of the extraction efficiency to optimize extraction conditions. The optimized conditions are listed in the following: temperature: 60℃, extraction time:1min,ionic liquid mass:4g,pH 7. Ions in environmental water such as calcium and magnesium do not interfere with the extraction of the ultra trace pesticide, their enrichment factors are in the range from 238 to 247. The linear range is the range of 0.81~2024 ng·L-1 for dicofol, 0.81~2075 ng·L-1for cypermethrin, 0.81~2049 ng·L-1 for fenvalerate and 2.1~2521 ng·L-1 for deltamethrin. Detection limit and good spiked recoveries for method of above extraction combined with GC-MS was found to be between 0.243 ng·L-1 and 0.63ng·L-1 and 91%~111%, respectively. The proposed method has been successfully applied to determination of ultra trace pesticides in environmental water samples.The dispersive phase micro-extraction has large contact area between analyte and acceptor phase, this results in remarkably reducing extraction time and increasing enrichment factors. Thus, analysts was widely and strongly interested in dispersive liquid phase micro-extraction in recent years. A procedure was developed for dispersive phase micro-extraction of ultra-trace DCF and the degeneration products of DCF in environmental water samples, in which ionic liquid 1-isooctyl-3-methylimidazolium hexafluorophosphate was used as extraction solvent and methanol as diffusion solvent. The optimum enrichment factors 785 for different pesticides was obtained with 0.5mL of 0.2g·mL-1ionic liquid-methanol solutions per 20mL of water sample with 0.01μgDCF. The linear range for the method of above extraction combined with GC-MS, detection limit and good spiked recoveries was found to be 0.255~637ng·L-1, 0.0765 ng·L-1and 99-112%, respectively. The proposed method has been successfully applied to determination of ultra trace pesticides in environmental water samples.
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