Electrochemical sensor based on nanostructured surface of reduced graphene oxide and gold nanoparticles containing electropolymerized poly-pyrrole for selective determination of limonene enantiomers in orange and pine essential oils

Limonene is a compound that has two isomers, (D)-limonene and (L)-limonene, found in different quantities and proportions in citrus fruits and pine tree species. In this work, the construction of the first electrochemical sensor based on nanostructured surface of reduced graphene oxide and gold nanoparticles containing electropolymerized poly-pyrrole for the enantioselective determination of limonene is reported. An analytical curve was obtained, with a limit of detection for (D)-limonene of 1.8 × 10−12 mol L−1, limit of quantification of 5.5 × 10−12 mol L−1, and amperometric sensitivity of 5.8 × 105 A L mol−1. For the (L) enantiomer, the corresponding values were 1.4 × 10−12 mol L−1, 4.3 × 10−12 mol L−1, and 6.2 A L mol−1, respectively. The developed sensor was applied for the determination of the two enantiomers in essential oils, where the concentration of (D) and (L)-limonene in orange oil was 8.7 × 10−2 ± 6.0 × 10−3 mol L−1 and 1.1 × 10−3 ± 2.0 × 10−4 mol L−1, respectively. For the concentration of limonene enantiomers in pine oil, the concentration found for (D) was 1.0 × 10−4 ± 1.5 × 10−5 mol L−1 and for (L) was 3.7 × 10−3 ± 3.3 × 10−4 mol L−1, demonstrating the different proportions of each enantiomer.