Acceptor-phase-free gel electromembrane extraction integrated with smartphone colorimetry for the quantification of cephalexin in pharmaceutical and environmental water samples

This work introduces an acceptor-phase-free colorimetric gel electromembrane extraction (G-EME) method integrated with a smartphone-based detection system as a simple and rapid method to quantify cephalexin in real samples. In this configuration, cephalexin migrates from the donor solution into the gel under an applied voltage of 30.0 V for 7.0 min, reacts with Fehling's reagent previously incorporated into the agarose gel to form a stable, colored copper complex. This design eliminates the need for a liquid acceptor phase, effectively solving common instability issues in conventional G-EME setups. Under optimized conditions, the method achieved a linear range of 50.0-250.0 μM with a limit of detection and quantification of 14.91 μM and 45.18 μM respectively. The effects of common interfering agents, including fructose, glucose, starch, and SO₄^2-, were studied. Furthermore, the method achieved a favorable greenness score, according to the Analytical GREEnness (AGREE) metric, because of its lack of use of organic solvents and minimal reagent consumption. The proposed method demonstrated good repeatability, when applied to commercial pharmaceutical capsules and environmental pond water, yielding relative recoveries between 90.20% and 107.55% with reliable intra-day and inter-day precisions (RSD% of 1.82% and 2.78%, respectively).