Simultaneous analysis of three metal ions on a single chip: Easy clean-up with bio-thin film in electromembrane extraction and quick colorimetric analysis with progressive web application

Abstract

In this study, a miniaturized on-chip electrically assisted membrane transport based on starch/gelatin thin-film, as a novel composite carbohydrate polymer, was introduced for the simultaneous determination of three heavy metal ions with an emphasis on green chemistry. The starch/gelatin membrane is environmentally friendly, has low cost, and can be used as a solvent-free membrane for ion transport and matrix cleanup. Metal ions were extracted by applying a low voltage across the membrane sheet. The acceptor droplets are specific ligand solutions that can form selective color complexes on the colorless membranes to indicate the presence of metal ions. The color response of the final acceptor droplets was evaluated by acquiring several digital images and processing them with specific software developed as a Progressive Web Application. For Ni(II), Cr(VI), and Cu(II), the limits of detections were 0.5, 0.5, and 0.1 mg/L, and limits of quantifications were 1.0, 1.0, and 0.5 mg/L, respectively. The calibration range is from 1.0 to 50.0 mg/L for Ni(II) and Cr(VI), while it is from 0.5 to 50.0 mg/L for Cu(II) with relative recoveries ranging from 86.6 to 113.3% and relative standard deviations less than 11.0%. The values obtained with AGREE and AGREEprep methods were 0.68, and 0.5, thus indicating a proper level of greenness for the proposed method. Finally, this method was successfully applied for measuring metal ions in solutions of acidified digested vegetables including lettuce, carrot, potato, and onion.