Triple-mode speciation of Fe²⁺ and Fe³⁺ using optical and paper-based digital imaging

Area of Science:

• Analytical Chemistry
• Environmental Science
• Materials Science

Background:

• Iron speciation (Fe2+ and Fe3+) is critical for environmental monitoring.
• Developing selective and sensitive detection methods for iron species remains a challenge.

Purpose of the Study:

• To synthesize and characterize a Schiff base probe, (Z)-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)benzoic acid (HNABA).
• To develop selective colorimetric, fluorometric, and smartphone-assisted paper-based digital sensing methods for Fe2+ and Fe3+ speciation.

Main Methods:

• Synthesis and characterization of the HNABA Schiff base probe.
• Spectroscopic analyses (UV-Vis, fluorescence, FTIR, NMR, ESI-MS) to confirm complex formation and binding mechanisms.
• Optimization of experimental parameters (pH, reaction time).
• Development of colorimetric, fluorometric, and digital paper-based sensing assays.

Main Results:

• The HNABA probe exhibited distinct optical responses to Fe2+ and Fe3+ via coordination with phenolic oxygen and imine nitrogen.
• Optimized methods achieved linearity ranges of 0.05-0.3 mg L-1 for both Fe2+ and Fe3+.
• Low limit of detection (LOD) values were obtained across all sensing techniques (0.015-0.03 mg L-1).
• High precision (RSD ≤ 3.4%) and satisfactory recoveries (97.6-99.0%) were observed in spiked water samples.

Conclusions:

• The HNABA probe facilitates selective iron speciation using multiple sensing modalities.
• The integrated optical and digital imaging platform provides a rapid, economical, and reliable tool for environmental iron monitoring.
• This approach holds significant potential for field applications in environmental analysis.