A dual-angle optoelectronic flow injection platform for ferrous ion (Fe2+) determination using blue LED excitation and solar cell detection

Abstract

Herein, a new optoelectronic flow injection method was proposed for the determination of ferrous ions (Fe²⁺) based on thiocyanate complexation to form a deep-red FeSCN²⁺ complex. The system used in this method included a home-built photometric platform, a dual-angle photonic irradiation spectrometer (DAPIS), with eight high-power blue LEDs (1.5 W each) as structured light sources and two photovoltaic solar cells as detectors. The LEDs were housed inside a brass enclosure of 2 mm inner diameter placed around a 100 mm flow quartz tube, allowing dual-angle irradiation (0–90° and 0–180° interaction by internal optical reflection effects). This geometry provided high photon utilization, reducing optical loss and improving detection sensitivity. A dual-line flow injection procedure based on the use of sodium persulfate (Na₂S₂O₈) as an oxidant and thiocyanate (SCN⁻) as a chromogenic reagent is presented herein. The linear dynamic range was between 0.2 and 17 mM, which was relatively wide, with an LOD of 8 µM and a correlation coefficient (r) of 0.99922, demonstrating the accuracy of the method and the reusability of the system. This method was successfully extended to pharmaceutical formulations and tested for statistical validation using the paired T-test (t-cal. (−0.184) < t-tab. (4.303)) as well as one-way ANOVA (F-cal. (0.069) < F-tab. (5.14)); no significant difference was observed between the proposed method and the conventional spectrophotometric methods. Owing to its modular design, high sensitivity, and adaptability to colorimetric, fluorometric, or turbidimetric reactions, the developed platform holds great potential for applications in environmental monitoring and agricultural analysis.