Determination of phthalate esters from food-contacted materials by on-line microdialysis and liquid chromatography

Phthalates (endocrine disrupters) released from food-contacted plastics into aqueous solution during microwave conditioning were measured with microdialysis enrichment on-lined high-performance liquid chromatography. The released phthalates in aqueous solution were diffused through a cellular dialysis membrane into the perfusion stream and thus enriched prior to HPLC analysis. Conditions for obtaining optimum enrichment such as the hollow dialysis fiber, flow-rate and polarity modifier in perfusion stream, pH, added-salt and stirring rate in sample solution, as well as chromatographic conditions were investigated. Experimental results indicated that microdialysis enrichment with a 20-cm polysulfone hollow dialysis fiber and heptane as the perfusate at 0.10-microL/min flow-rate to collect phthalates from aqueous sample in 0.5M KCl matrix (optional pH) at 250 rpm stirring offered the optimum enriched efficiency. The dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP) were well separated within 16 min by a C-18 column and eluted gradient from 40 to 90% aqueous acetonitrile (at pH 6.0) and 1.0 to 1.5 mL/min flow-rate. Detection was carried out with an UV detector at 225 nm. The enrichment factors were 14, 140 and 201 (at 0.10-microL/min perfusate flow-rate) for DMP, DEP and DBP, respectively, with less than 4% RSD. The proposed method provided a very simple, fast and eco-friendly enriched procedure to determine the extent of phthalates migration from disposable plastic materials into drinking soup.