Determination of five phthalate esters in running water and milk by micellar electrokinetic capillary chromatography

Abstract

A simple, reproducible and sensitive micellar electrokinetic chromatography method was developed for the separation and determination of dimethyl phthalate (DMP), diethyl phthalate (DEP), dibuthyl phthalate (DBP), dihexyl phthalate (DHP) and bis(2-ethylhexyl) phthalate (DEHP) in running water and milk. Field-enhanced sample injection with reverse migrating micelles was used for on-line preconcentration of the analytes. The buffer contained 50 mM H3PO4–NaOH, 160 mM sodium dodecyl sulfate (SDS), 15% acetonitrile and 20% 2-propanol, at the pH of 2.0. The sample solution was diluted with water containing 5 mM SDS and injected for 5 s with–20 kV after gravity injection of 5 s water plug at 20 cm high. Under the optimum conditions, the analytes were well separated and by optimizing the stacking conditions, about 51, 62, 57, 48 and 43 fold improvement in the detection sensitivities were obtained for DMP, DEP, DBP, DHP and DEHP, respectively. The instrument detection limits (S/N = 3) of DMP, DEP, DBP, DHP and DEHP were 0.1, 0.05, 0.05, 0.02 and 0.05 µg/mL, respectively. The recoveries of DMP, DEP, DBP, DHP and DEHP in water were 86.9–98.7, 88.9–105.2, 91.7–109.4, 93.0–108.2 and 91.0–99.2%, respectively. The phthalates were successfully determined in running water and milk with satisfactory repeatability and recovery. The contents of DEHP and DHP in the running water were 0.45 and 1.23 µg/mL, respectively. The other analytes were not detected in the analyzed running water and milk.