Activated silica gel based carbon paste electrodes exhibit signal enhancement for quercetin

Silica gel was activated using 6.0 M hydrochloric acid, and then used to modify a carbon paste electrode. The particle size of silica gel was significantly reduced by the activation, as confirmed by scanning electron microscopy measurements. Electrochemical behaviors of K3[Fe(CN)6] on the modified electrode revealed that activated silica gel was capable of facilitating electron transfer and increasing surface area. Chronocoulometry tests indicated that activated silica gel exhibited a strong accumulation efficiency toward quercetin. As a result, activated silica gel displayed remarkable enhancement effect, and greatly increased the oxidation signals of quercetin. The oxidation mechanism of quercetin was also investigated. It was found that the oxidation of quercetin involved two electrons and two protons, occurring at two phenolic hydroxyl groups. The influences of pH value, amount of activated silica gel, accumulation potential and time on the signal enhancement of quercetin were discussed, and a novel electrochemical method was developed for the detection of quercetin. The linear range was from 5 to 100 μg L−1, and the limit of detection was 3.53 μg L−1 after 2 min accumulation. Finally, this method was successfully used in honeysuckle and tea samples.

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► Activation of silica gel decreased particle size and enhanced accumulation ability.
► Activated silica gel greatly increased the oxidation signal of quercetin.
► Oxidation was attributed to phenolic hydroxyl groups and transferred two electrons.
► A sensitive and simple electrochemical method was developed for quercetin detection.