Simultaneous extraction and colorimetric detection of ions using gel electromembrane

Abstract

A total integrated electrocolorimetric sensing approach consisting of gel-based electromembrane extraction and colorimetric detection in one-step process was developed. This system was designed using colorimetric reagents preadded to the agarose gel for the determination of the following two model analytes: iodide for negative ions and nickel for positive ions. In this system, when a voltage was applied, the analytes were extracted and transferred from the sample solution (donor phase) to the gel (acceptor phase). The analytes then simultaneously reacted with the colorimetric reagents inside the gel, yielding blue and pink colors for iodide and nickel ions, respectively. These colors were then analyzed using a portable spectrometer for iodide detection and smartphone for nickel detection, which could also be distinguished with the naked eye. Parameters affecting the extraction efficiency were studied and optimized for both analytes. The gel composition for iodide detection was 4% (w/v) agarose, 5% (v/v) H2O2, and 1% (w/v) starch in 2 mM HCl. The gel composition for nickel detection was 3% (w/v) agarose and of 50% (%v/v) of 1:1 Dimetylglioxime (0.03 mM): Ammonia (80 mM) in agarose gel. Iodide and nickel were extracted at applied potentials of 50 and 70 V, and extraction time of 15 and 5 min and a stirring rate of 600 rpm, respectively. Under the optimized conditions, the developed systems provided linear responses within 15 min for iodide concentrations ranging from 50 to 250 µg L-1 with a detection limit of 18 µg L-1 and for nickel concentrations ranging from 30 to 750 µg L-1 with a detection limit of 1 µg L-1. Finally, these systems were successfully applied to the determination of iodide in iodide food supplement samples and nickel in chocolate samples, showing a negligible matrix effect. This integration could also be extended to other analytes and detection systems to develop sensitive, simple, and environmentally friendly sensing approaches.