Journal
MICROCHIMICA ACTA
Volume 185, Issue 7, Pages -Publisher
SPRINGER WIEN
DOI: 10.1007/s00604-018-2893-4
Keywords
Gold nanoparticles; Cyclic voltammetry; Oregano; Thyme; Surface plasmon resonance; Folin-Ciocalteu
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Funding
- NANOAVANSENS program from Community of Madrid [S2013/ MIT-3029]
- Spanish Ministry of Economy and Competitiveness [CTQ 2014-58643-R]
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An extraction-free method is described for the colorimetric determination of thymol (TY) and carvacrol (CA) isomers in essential oils by making use of the pH-dependent formation of gold nanoparticles (AuNPs). In solutions of pH 12, TY and CA form gold nanoparticles, while at pH <= 11 only CA does so. By taking advantage of this finding, two different approaches based on colorimetric assay (absorption at 550 nm) were developed: one at pH 12 for the determination of total CA and TY, and other at pH 9 and pH 12 for differential quantification of TY and CA. The former agrees with the well-established Folin-Ciocalteu method, and the latter provides a simple way for calculation of TY/CA ratio. The linear ranges are from 100 to 1000 mu M at pH 9, and from 50 to 200 mu M at pH 12. The limits of detection are 0.09 mu M at pH 9, and 0.02 mu M at pH 12. These features make this method simple, fast and reliable. Conceivably, it can be used to assess the quality of essential oils and may become a valuable alternative to more sophisticated, laborious and high time-consuming methods.
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