LEGO^® brick supporting a thermo-responsive sorptive phase: a modular platform for circular sample preparation

This work is framed within the paradigm of Circular Analytical Chemistry (CAC), which promotes the integration of waste-derived materials, minimization of resource consumption, and development of near closed-loop analytical procedures. In line with this prevailing trend, we present a proof-of-concept extraction device constructed entirely from LEGO^® bricks, serving as supports for a thin coating composed of carboxylated multi-walled carbon nanotubes dispersed in L-menthol (1.3% w/w). The proposed tool combines a modular and reusable plastic support, with a sorptive phase derived from renewable and low-impact components. The extraction procedure was applied to the extraction of eight common pesticides from tap water samples thanks to the adsorption properties of the coating layer, solid at room temperature; after the adsorption, the analyte was recovered employing the thermo-responsive properties of the sorbent, by placing the brick in a beaker and heating at 60 °C to melt menthol. The extract was diluted with isopropanol and directly injected in the UPLC-DAD/MS system. The workflow is nearly zero-waste, requiring only 200 µL of isopropanol to wash the brick and avoid solidification of the menthol extract, which can be directly injected for the chromatographic analysis after centrifugation. Besides its sustainable design, the method demonstrates good analytical performance, with average recoveries ranging from 86.6 to 113%, precision between 2.7 and 15%, and limits of quantification ≤ 0.15 µg L^- 1, comparable or even better than conventional extraction techniques. Besides analytical performance, this approach embraces the concepts of recycling, moving beyond the traditional approaches of Green Analytical Chemistry toward strategies that valorise waste materials and pursue the broader goals of CAC.