Natural deep eutectic solvent-based liquid phase microextraction in a 3D-Printed millifluidic flow cell for the...

At present, 3D printing technology is becoming increasingly popular in analytical chemistry because it enables the rapid and cost-effective manufacture of sample preparation devices, particularly in flow-based operation, opening up new opportunities for the development of automated analytical methods. In parallel, the use of miniaturized methods and sustainable solvents in sample preparation is highly recommended. Accordingly, in this work, a 3D-printed millifluidic device was designed and used for the on-line natural deep eutectic solvent (NADES)-based liquid phase microextraction (LPME) coupled to a spectrofluorometer for, as a proof of concept, the determination of thiabendazole (TBZ) in fruit juice samples.

The millifluidic device was 3D printed by stereolithography and consisted of two patterned plates, each containing a millichannel (acceptor and donor channel). The millichannels were separated by a polypropylene membrane impregnated with optimal NADES, acting as a supported liquid membrane (SLM). Among the NADES investigated, formic acid:L-menthol (1:1 M ratio) was selected as the SLM, avoiding the use of conventional harmful organic solvents. The proposed millifluidic device was successfully applied to the determination of thiabendazole in fruit juice samples, achieving LOD and LOQ values of 0.45 μg L^-1 and 1.42 μg L^-1, respectively, which are well below the maximum residue levels (MRLs) set by the European Union. The greenness and applicability of the proposed analytical method were evaluated using the AGREEPrep, SPMS and BAGI tools and compared with other published methods. In general, the proposed method was superior to others, mainly due to its high sensitivity and high sample throughput.

Several cells were easily designed with different channel geometries (length and depth) to find the optimal dimensions, and then 3D printed and tested in a relatively fast, cheap and simple way, demonstrating the suitability of 3D printing in the fabrication of millifluidic devices as an alternative to traditional fabrication techniques. In addition, the proposed approach is fully compatible with new sustainable solvents, facilitating the development of green sample preparation methods.