In this present study, 1-butyl-3-methylimidazolium chloride ([C 4 MIM]Cl), 1-octyl-3-methylimidazolium chloride ([C 8 MIM]Cl), and 1-decyl-3-methylimidazolium chloride ([C 10 MIM]Cl) were adopted as mobile phase additives in the high performance liquid chromatography (HPLC) to simultaneously separate phenoxy acid herbicides and phenols at neutral pH. It was found that by using 20 mM of [C 4 MIM]Cl, baseline separation and good chromatograms for all the acid compounds were obtained on a normal reversedphase C 18 column. The retention time of the target acid compounds shortened with the increase of the alkyl chain length and the concentrations of ionic liquids, probably due to the delocalization of the positive charge on the imidazolium cation, the repulsion between chlorine ions of ionic liquids and the acid compounds, as well as the stereo-hindrance effect. The mechanism with ionic liquids as mobile additives for the separation of acid compounds was discussed.
Traces of phenoxy acid herbicides and phenols were determined in environmental water samples by high performance liquid chromatography (HPLC) coupled to thin liquid film extraction (TLFE). A TLFE sampling device was prepared by dipping pieces of a polypropylene microporous hollow fiber membrane into dihexyl ether (containing 10% tri-n-octylphosphine oxide as carrier) for a few minutes to impregnate the pores of the hollow fiber wall. Extraction of analytes takes place from the outer aqueous phase into the immobilized solvent. After extraction the removal of the organic solvent was accomplished with a few µl of methanol which was used for HPLC analysis. Enrichment factors as high as 446 were obtained for the target compounds. The method provided detection limits as low as 0.4-1.2 µg L −1 , good repeatability (the RSD ranging from 2.1 to 6.3%, n=5) and a linear range from 2 to 200 µg L −1 for the target compounds. Real sample analysis showed recoveries between 84.6% and 112% for all compounds investigated.
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