Sensitive determination and electro-oxidative polymerization of azodyes on a carbon paste electrode modified with bentonite

• A bentonite modified C paste electrode (BentMCPE) was developed for dye determination.
• The detection limits for LR2B, AB113 and AY17 were as low as (6–8) × 10− 10 mol/L.
• The repetitive CV scans cause to electro-catalytic anodic polymerization of the dyes.
• Electro-polymerization of the dyes was proceeded by azo/hydrazone intermediates.
• A mechanism was proposed proceeding by head to tail interactions of the radicals.

A new composite carbon paste electrode incorporating bentonite (BentMCPE) was developed and used for extremely sensitive determination and electro-oxidative polymerization of azodyes using cyclic voltammetry. Lanaset Red 2B (LR2B) was selected as a model molecule for optimization of operational parameters such as amount of modifier, the pH of buffer medium, scan rate and dye concentration. Performance analyses showed that BentMCPE allows determination of LR2B, Acid Blue 113 (AB113) and Acid Yellow 17 (AY17) dyes as low as (6–8) × 10− 10 mol/L at pH 5.5. The peak intensities increased with the repetitive scans due to electro-catalytic anodic polymerization of the dyes. The results of multiple scans in single binary and ternary dye solutions showed that all of the dyes whether hydroxyl substituted (LR2B and AY17) or not (AB113) can be polymerized on the BentMCPE surface. Two possible electro-polymerization pathways were proposed by assuming formation of different radical intermediates produced from azo/hydrazone tautomers of the dyes. A comparison of FT-IR spectra recorded after the first and tenth repetitive scans confirmed that the electro-polymerization process proceeds by head to tail interactions of the radicals with dye monomers deposited on the electrode surface.

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