Analysis of phthalates via HPLC-UV in environmental water samples after concentration by solid-phase extraction using ionic liquid mixed hemimicelles

Ionic liquid mixed hemimicelles-based solid-phase extraction for the preconcentration of five phthalates in environmental water sample was investigated in this paper. A comparative study on the use of room temperature ionic liquids (RTILs) 1-hexyl-3-methylimidazolium bromide ([C6mim]Br) and 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br)-coated silica as sorbents was presented. Owing to having bigger adsorption amounts for analytes [C12mim], Br-coated silica was selected as SPE material and the five analytes di-ethyl-phthalate (DEP), di-n-propyl-phthalate (DnPP), di-n-butyl-phthalate (DnBP), di-cyclohexyl-phthalate (DcHP) and di-(2-ethylhexyl)-phthalate (DEHP) can be quantitatively extracted under optimal conditions. The analytes retained on the cartridge were desorbed completely with 3 mL methanol (pH 2). Predominant factors influencing the extraction efficiency, such as RTILs concentration, pH value, ionic strength and breakthrough volume were discussed. The proposed method had been applied to determining the five phthalates in four environmental water samples and concentration factor of 600 was achieved easily. Detection limits obtained ranged between 0.12 and 0.17 μg/L. The accuracy of this method was evaluated by recovery measurement on spiked samples, and good recovery results (85–107%) with relative standard deviation (R.S.D.) of below 6% were achieved.