Development of a dispersive liquid–liquid microextraction method for the determination of plastic additives in seawater

Abstract

A method using dispersive liquid–liquid microextraction (DLLME) prior to high performance liquid chromatography-diode array detection (HPLC-DAD) was developed to determine seven additives from the plastics industry (butylated hydroxytoluene, diisodecyl phthalate, irgafos 168, lawsone, quercetin, triclosan and vitamin E) in seawater samples. These compounds can reach seawater due to direct discharge from wastewater treatment plants and leaching from plastics and microplastics. The extraction was performed using 25 mL of seawater, 500 μL of 1-octanol (extraction solvent) and a stirring step instead of dispersive solvent. Additive concentrations were determined by LC-DAD on a C18 column with a mobile phase of acetonitrile and phosphoric acid aqueous solution (pH 3.5) by gradient elution. The analytical recoveries ranged from 82 to 93% for all compounds, except for lawsone (60%). Repeatability and intermediate precision were adequate with RSD < calculated values following the Horwitz equation at the concentration levels evaluated (0.06 and 0.24 mg L⁻¹). All additives exhibited linear matrix calibration curves (R² > 0.99). Detection limits ranged from 0.009 to 0.028 mg L⁻¹ and quantification limits ranged from 0.027 to 0.084 mg L⁻¹. Finally, the application of the method to real samples verified the method as accurate and applicable to seawater.