3D printed extraction devices in the analytical laboratory—a case study of Soxhlet extraction

Abstract

3D printing was introduced in the 1980s but only now has gained widespread acceptance among practitioners because of (i) the friendlier software interfaces for digital computerassisted designs (CAD), and the ensuing computer-assisted manufacturing (CAM) of the 3D object; (ii) availability of low-cost custom-grade printers; and (iii) the advantages that present against milling or other classical subtractive technologies, that is, enables complicated geometries to be easily designed in a single step, generates minimum residues, and allows fast prototyping. Chemists have followed this trend and incorporated 3D printers in their research laboratories and lecture halls, demonstrating the possibilities of this technique in a plethora of academic publications [1–3]. Notwithstanding the versatility of the printed educational resources, their applicability in the analytical chemical laboratory has not yet attracted much attention because of the limited chemical compatibility [4–8] of the majority of polymeric 3D prints: Their chemistry is polar (methacrylate-epoxy, polylactic acid, nylon, and acrylonitrile butadiene styrene), and thus, solvents, acids, or aggressive reagents put the stability of the prints in jeopardy. This may be the reason why most of the applications found in the chemistry literature resort to visualization of tridimensional structures [1, 9, 10], fabrication of non-wetted mechanical supports [11, 12], or disposable microfluidic chips [7, 13] that can merely perform a handful of unitary processes before the wetted surface gets degraded or some chemical components of the process sorb onto it irreversibly. A key player remains hidden in the shadows of this complex landscape: the 3D printed polar objects are superbly compatible with the majority of non-polar solvents [5, 14] and those fabricated with stereolithography (SLA) are also watertight and transparent, a triple-win situation in the teaching domain. Low-cost SLA printers of less than 200 € are available, work without need of a computer connection [15], have a minimal footprint, and the only safety concerns are the minimally irritant resin and volatile components in the course of the printing process. Given the potential of 3D printing and the leading role that chemists will play in its development, the presentation of this technique to the young generation of chemists at the undergraduate level is not only capital but also fostered by the new guidelines of European Higher Education Area [16, 17] as a transversal and interactive competence. Aspects that might become pivotal in the development of methods for analytical chemists are (i) the fast, transparent, and watertight 3D printed prototypes, (ii) their chemical compatibility that must be carefully assessed for the different analytical applications, (iii) the reversed phase or cation exchange capabilities of the polymers [4], and (iv) the possibility that the uncured resin components contaminate the sample by leaching monomers and oligomers. The solid-liquid extraction of hydrophobic compounds from environmental solids is an analytical application very well suited to the analytical chemistry laboratory in which 3D prints can be leveraged because it avoids light eluotropic solvents and very high temperatures. To this end, we herein introduce a laboratory exercise for the “Integrated Analytical Chemistry Laboratory” (last semester of the BSc in Chemistry (year 4) at the University of the Balearic Islands, Spain) that aims to exploit 3D printing in extraction technologies. The students will design and prototype their own Soxhlet extractor by SLA whereupon it will be employed in a sediment analysis workflow, by attaching it to standard glassware, such as an Erlenmeyer flask and Liebig condenser, for extraction of * David J. Cocovi-Solberg [email protected]