Development and Application of a Schiff-Base Colorimetric Sensor for Lead (Pb²⁺) Detection in Borehole Water from Kaduna Metropolis, Nigeria

Groundwater accessed through boreholes constitutes a major source of domestic water supply in many Nigerian cities, including Kaduna metropolis. However, increasing urbanization and industrial activities have heightened concerns about heavy metal contamination, particularly lead (Pb²⁺), which poses severe health risks even at low concentrations. Conventional analytical techniques for lead determination, such as atomic absorption spectroscopy and inductively coupled plasma–based methods, although highly sensitive, are often limited in routine application by cost, infrastructural requirements, and technical expertise in resource-limited settings. This study reports the synthesis, spectroscopic characterization, and application of a Schiff-base ligand as a simple colorimetric sensor for Pb²⁺ detection in borehole water. The ligand was synthesized via condensation of salicylaldehyde and ethylenediamine, yielding a yellow crystalline solid (melting point 189–191°C, yield 78.4%). Fourier transform infrared spectroscopy confirmed azomethine formation and coordination through nitrogen and oxygen donor atoms, while UV–Visible spectroscopy revealed characteristic π→π* and n→π* transitions and the emergence of a ligand-to-metal charge transfer band at 445 nm upon Pb²⁺ binding, accompanied by a visible color change. Quantitative evaluation showed linear Beer–Lambert behavior (R² = 0.995) over the investigated concentration range. The sensor exhibited high selectivity toward Pb²⁺ over common interfering metal ions. Application to twelve borehole water samples collected across Kaduna metropolis produced recovery values of 92–98% with relative standard deviations below 3%, indicating good accuracy and precision. The results demonstrate the potential of the developed Schiff-base colorimetric sensor as a low-cost and effective tool for preliminary screening of lead contamination in groundwater.