A Vanillin-Derived Chloro-Benzimidazole Schiff Base as a Chromogenic Reagent for Spectrophotometric Determination of Pb (II) and Ciprofloxacin

Walaa Mohammed Najem

doi:10.46796/ijpc.v7i2.947

Walaa Mohammed Najem College of Medical Laboratory Techniques, Imam Ja'afar Al-Sadiq University, Najaf, Iraq

DOI https://doi.org/10.46796/ijpc.v7i2.947

Abstract

The Schiff base (Z)-4-(((2-(6-chloro-3a,4-dihydro-1H-benzo[d]imidazol-2-yl)phenyl)imino)methyl)-2-methoxyphenol (compound 23, C₂₆H₂₀ClN₅O₃) resulted from condensing 2-amino-6-chloro-1H-benzimidazole with vanillin, and FT-IR, ¹H-NMR, and ¹³C-NMR confirmed the expected structure. We then examined whether this compound could detect Pb(II) by UV-Vis spectrophotometry. Mixing the reagent with Pb(II) in ethanol-water at pH 6.5 turned the solution reddish-brown (λmax shifting from 425 to 510 nm). Full color development took 15 min at room temperature. Job’s method gave a 1:2 (M:L) ratio. The calibration was linear across 0.5-12.0 µg/mL (ε = 1.85×10⁴ L mol⁻¹ cm⁻¹, Sandell sensitivity 11.2 ng cm⁻²), with LOD and LOQ of 0.091 and 0.305 µg/mL. The calculated β₂ (1.02×10⁸ M⁻²) and thermodynamic quantities (ΔH = −27.1 kJ/mol, ΔS = +62.4 J/mol·K, ΔG = −45.8 kJ/mol) indicate spontaneous, exothermic complex formation. Spiked tap water and Euphrates river water samples gave Pb(II) recoveries of 98.2-98.3%. Reagent (23) was also applied to ciprofloxacin tablets by an indirect route: adding ciprofloxacin displaced Pb(II) from the compound 23 complex, reducing the 510 nm absorbance in proportion to drug concentration over 0.5-10 µg/mL (LOD = 0.157 µg/mL). Tablet recoveries fell between 98.5 and 98.8%, with no interference from common excipients.

Keywords: Benzimidazole Schiff base, Vanillin, Spectrophotometric determination, Lead(II); Chromogenic reagent, Ciprofloxacin, Pharmaceutical analysis, Formation constant

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