Extraction-free colorimetric determination of thymol and carvacrol isomers in essential oils by pH-dependent formation of gold nanoparticles

TONELLO, NATALIA VERÓNICA; D?ERAMO, FABIANA; MARIOLI, JUAN MIGUEL; CREVILLEN, AGUSTÍN G.; ESCARPA, ALBERTO

MIKROCHIMICA ACTA

SPRINGER WIEN

Lugar: Viena; Año: 2018 vol. 185

0026-3672

An extraction-free method is described for the colorimetric determination of thymol (TY) and carvacrol (CA) isomers in essentialoils by making use of the pH-dependent formation of gold nanoparticles (AuNPs). In solutions of pH 12, TYand CA form goldnanoparticles, while at pH ≤ 11 only CA does so. By taking advantage of this finding, two different approaches based oncolorimetric assay (absorption at 550 nm) were developed: one at pH 12 for the determination of total CA and TY, and otherat pH 9 and pH 12 for differential quantification of TY and CA. The former agrees with the well-established Folin-Ciocalteumethod, and the latter provides a simple way for calculation of TY/CA ratio. The linear ranges are from 100 to 1000 μMat pH9,and from 50 to 200 μM at pH 12. The limits of detection are 0.09 μM at pH 9, and 0.02 μMat pH 12. These features make thismethod simple, fast and reliable. Conceivably, it can be used to assess the quality of essential oils and may become a valuablealternative to more sophisticated, laborious and high time-consuming methods.