Enhanced-oxidation and electrochemical determination of honokiol and magnolol using NMP-exfoliated graphene nanosheets

Using N-methyl-2-pyrrolidone (NMP) as the exfoliation solvent, graphite powder was easily exfoliated into graphene nanosheets (GS) via ultrasonication, which was characterized using transmission electron microscopy. The measurements of scanning electron microscopy and atomic force microscopy indicated that the modification of GS obviously increased the surface roughness of glassy carbon electrode, providing high accumulation efficiency and large response surface. As a result, the oxidation signals of honokiol and magnolol were increased greatly on the surface of GS. Moreover, the oxidation mechanisms were studied for honokiol and magnolol, and one electron was transferred in the oxidation process. After optimizing the parameters such as pH value, amount of GS, accumulation potential and time, a highly-sensitive electrochemical sensor was developed for the simultaneous determination of honokiol and magnolol. The values of detection limit were evaluated to be 0.2 μg L^-1 and 1.0 μg L^-1 for honokiol and magnolol. The application of this sensor was demonstrated using Chinese traditional medicines, and the accuracy and feasibility were tested to be good using high-performance liquid chromatography.