Methylparaben (MP) is one of the most frequently used as preservatives in cosmetic products due to its antimicrobial properties, low toxicity, good stability, and low cost. Even though MP has low impact, a high amount of MP can be harmful to consumer health. The U.S. Food and Drug Administration limited the use of parabens in food is not more than 0.1 % wt and 0.01 - 0.3 % wt for cosmetics. Therefore, the detection of MP in food or cosmetics is important.
In this study, the electrochemical sensor for MP is developed based on the gold-carbon nanomaterial composites modified pencil graphite electrode (PGE). The activated carbon (AC) and graphene oxide (GO) were firstly used to modify on PGE surface, followed by the electrodeposited of gold nanoparticles on the carbon modified surfaces (denoted as AuNP@AC and AuNP@GO, respectively. The parameters affecting detection performances including the square wave voltammetry and modified electrode parameters were optimized to provide the highest response and repeatability. The modified electrodes with optimal parameters display enhanced electroactivity for the oxidation of MP without surface fouling effect compared to the unmodified PGE. Both AuNP@AC and AuNP@GO provided the same linearity in the range of 0.050 - 0.75 mM and 3.0 – 10.0 mM with 0.030 mM limit of detection for both modified electrodes. High repeatability and reproducibility were obtained with %RSD lower than 3.36 - 3.51 %. Over 40 times can be used for a prepared electrode with 80% remaining responses representing high stability. Finally, the developed method was applied to detect MP in 3 cosmetic samples. The real sample analysis showed good agreement results obtained from the high-performance liquid chromatography with diode-array detector with acceptable percentage recoveries ranging from 90 – 102 %.