pH-controlled voltammetric behaviors and detection of phytohormone 6-benzylaminopurine using MWCNT/GCE

• pH-controlled voltammetric behaviors of 6-BA was explained.
• Protonation–dissociation equilibria of 6-BA was proposed.
• Electrocatalytic oxidation mechanism of 6-BA was proposed.
• 6-BA was detected using adsorptive stripping voltammetry at MWCNT/GCE.

The electrochemical detection of phytohormones is extremely difficult owing to their poor electrochemical activities, strong electrode passivation (fouling), and complicated electrochemical behaviors and reaction mechanism. In this paper, an interesting electrochemical phenomenon on voltammetric behaviors for the electrochemical oxidation of 6-benzylaminopurine (6-BAP) which was one of the well-known phytohormones under the different pH conditions was investigated, and the content of 6-BAP in real samples was detected by the adsorptive stripping voltammetry using MWCNT/GCE. The pH-controlled voltammetric behaviors like peak potentials, peak currents, peak shapes and peak number of 6-BAP were discussed by the protonation–dissociation equilibria of 6-BAP in combination with electrocatalytic oxidation mechanism of 6-BAP. The electrochemical sensing performance such as the linear range, limit of detection (LOD), limit of quantification (LOQ), sensitivity, selectivity, precision and applicability for the pH-controlled stripping voltammetric detection of 6-BAP was also evaluated. There was an observable difference in the number of peaks for the electrochemical oxidation of 6-BAP under strong acidic (three peaks), near neutral (two peaks), and strong alkaline (one peak) pH conditions. The electrochemical oxidation reaction of 6-BAP was adsorption-controlled irreversible processes, which were not affected by three different pH values. Oxidation peaks with relatively well-defined peak shapes and high peak currents were selected for the adsorptive stripping voltammetric detection of 6-BAP, and peak currents were proportional to 6-BAP concentrations in linear ranges of 0.3–50 μM with LOD of 0.098 μM and LOQ of 0.326 μM at pH 3.0, 0.5–60 μM with LOD of 0.165 μM and LOQ of 0.545 μM at pH 7.0, and 0.7–60 μM with LOD of 0.235 μM and LOQ of 0.776 μM at pH 10.0. The adsorptive stripping voltammetric determination of 6-BAP content with real samples in acid solution was more feasible and applicable.

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