Electrochromatographic separations of multi-component metal complexes on a microfluidic paper-based device with a simplified photolithography

Electrochromatographic separations of three metal complexes were achieved through observing the visualization evolution process of moving chelation boundaries (MCBs) on microfluidic paper-based analytical devices (mu PADs). A simplified photolithography was developed to pattern the mu PADs within 5-10 min with three steps only, manually gelatinize, expose and develop, through thinning SU-8 2150 with trichloromethane. With a cutting method, many bubbles were clearly observed in the single-component MCB system on the mu PADs, but were not found with this photolithography method under the same voltages. It was demonstrated that this photolithography for patterning narrow paper channels rejected Joule heating more effectively than the cutting paper method did. It was observed simultaneously that the apparent distances of electrophoretic and electroosmotic migrations of the blue [Cu-EDTA](2-) chelation boundary increased with increasing electrical field strength and width of the paper channels, respectively. The higher the Cu2+ concentrations were, the slower the electrophoretic migrations of the blue boundary were, and the faster the electroosmotic migrations of the blue boundary were on the mu PADs with this photolithography. The separations and concentrations of the coloured zones, pink [Co-EDTA](2-), blue [Cu-EDTA](2-) and yellow [Fe-EDTA](2-), were clearly observed in the applied electric fields on the mu PADs. The studies benefit extending the application of mu PADs as low-cost, disposable analysis tools and deepen understanding of the comprehensive mechanisms concerning MCBs, partition adsorption and electroosmotic flow on mu PADs.