Preconcentration of nanoplastics using micro-electromembrane extraction across free liquid membranes

Asymmetric micro-electromembrane extraction (µ-EME) based on a free liquid membrane has been evaluated for the preconcentration of nanoplastics. A conical unit (200 µL micropipette tip) enabled the simple and reproducible formation of the required three-phase extraction system consisting of a donor solution (150 µL sample/standard solution), free liquid membrane (FLM; 10 µL 1-pentanol), and an acceptor solution (5 µL of 5 mM phosphate buffer, pH 10.7). After µ-EME, nanoplastics transferred across the FLM into the acceptor solution were quantified using capillary zone electrophoresis with diode array detection. Enrichment factors >20 and extraction recoveries >70 % were achieved for nanoplastics concentrated at 500 V during 5 min. The limit of detection (LOD, S/N = 3) and limit of quantification (LOQ, S/N = 10) of the method using 200 nm sulphonated polystyrene particles as model nanoplastics were 6.00×10⁻⁴% (w/v) and 2.00×10⁻³% (w/v), respectively. Intraday (n = 6) and interday (n = 6) repeatability%RSD for 5.5 × 10⁻³% (w/v) nanoplastics were 8.5 % and 7.2 %, respectively. µ-EME enabled an efficient sample matrix clean-up and preconcentration of nanoplastics spiked in tea sample matrices. Nanoplastics preconcentrated through the FLM for black tea resulted in an enrichment factor of 20±3.6 (n = 3), with complete sample matrix removal of UV absorbing compounds.