Using water plug-assisted analyte focusing by micelle collapse in combination with microemulsion electrokinetic chromatography for analyzing phthalate esters

• A water plug-assisted analyte focusing by micelle collapse in combination with microemulsion electrokinetic chromatography (WPA-AFMC-MEEKC) method is developed.
• Sensitivity enhancement is approximately 100 folds in comparison to the conventional MEEKC method.
• The method is successfully applied to pediatric pharmaceuticals for screening of phthalate esters.

Phthalate plasticizers are widely used in the plastics industry, but they have been detected in soft drinks, pharmaceuticals and food products. This study developed a method that uses water plug-assisted analyte focusing by micelle collapse and microemulsion electrokinetic chromatography (WPA-AFMC-MEEKC) for quantifying benzyl butyl phthalate (BBP), dibutyl phthalate (DBP), diethylhexyl phthalate (DEHP), and diisodecyl phthalate (DIDP) in pediatric pharmaceuticals. The AFMC strategy was applied to improve the detection sensitivity, and a short water plug was introduced to assist micelle collapse in the micelle dilution zone for sample stacking. To carry neutral phthalates into the capillary through electrokinetic injection, sodium dodecyl sulfate (SDS) was added to the sample solution, and 8 mM SDS was selected as the optimal concentration. The optimized background solution (BGS) contained 16.13 mM phosphate buffer (pH = 2.5), 150 mM SDS, 0.75% n-octane (v/v), 5% 1-butanol (BuOH), 22.5% acetonitrile (ACN), and 15% isopropanol (IPA). Under the optimal separation conditions, four phthalates could be quantified within 20 min with enhancement factors of 58, 200, 86 and 90 for DIDP, DEHP, BBP, and DBP, respectively, compared to the conventional MEEKC mode. The limits of detection were within the range of 0.047–0.010 μg mL−1. The accuracy of the method was within the range of 96–117%. The WPA-AFMC-MEEKC method was applied for the analysis of six pediatric pharmaceuticals, and the results demonstrated that the developed method is sensitive and accurate, allowing it to be used for quality control of pediatric pharmaceuticals.