Multivariate approach in voltammetric identification and simultaneous determination of eugenol, carvacrol, and thymol on boron-doped diamond electrode

Abstract

The paper presents multivariate partial least-squares calibration model defined for the identification and simultaneous determination of phenolic terpenoids-eugenol, carvacrol, and thymol-by means of the differential pulse voltammetry. For the first time, using boron-doped diamond electrode signal, electrochemical distinction of carvacrol and thymol, despite the short distance between the peaks (15 mV), was described. The analytes' concentrations applied in the calibration model were selected using the 3-factorial central composite design. The multivariate partial least-squares model, with optimized data pre-processing, was used for determination of eugenol, carvacrol, and thymol in the concentration ranges of 0.77-13.86, 0.58-10.40, and 0.73-7.32 mg/dm 3 , respectively. The quality of the method, expressed by the root-mean-squared error of calibration was 0.55, 0.20, and 0.26 mg/dm 3 for the specified analytes. The recovery in the analysis of the pure signals was 98.92%, 101.62%, and 101.46%, what confirmed the possibility of clearly distinguishing the thymol and carvacrol peaks. In the spiked honey samples, the accuracy of eugenol, carvacrol, and thymol determination, expressed by the root-meansquared error of prediction, was in the range 0.20-0.83 mg/dm 3 , and recovery in the range 80.9-111.9%. Application of the presented model not only enables electrochemical identification and simultaneous determination of eugenol, carvacrol, and thymol, but also allows rapid, accurate, and low-cost verification of authenticity of the commercial products.

Voltammetric Determination of Isopropylmethylphenols in Herbal Spices

“…Owing to the difference of only 0.005 V between the peak potentials for THY and CAR, it is difficult to distinguish their voltammetric peaks. These results confirm the earlier observations taken from water solutions [ 28 , 46 ]. Therefore, only their total content can be voltammetrically determined.…”

“…Voltammetric techniques are based on the anodic oxidation of thymol and carvacrol [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. From the data described in the literature, it is possible to conclude that the electrode process of THY and CAR on different electrodes and in different solutions is characterized as irreversible [ 26 , 27 , 28 , 32 , 33 , 34 , 35 , 37 , 40 , 41 ], controlled by diffusion [ 27 , 31 , 32 , 33 , 35 , 36 , 39 , 40 , 41 ] or adsorption [ 34 , 37 ], and it involves an exchange of one electron and one proton [ 30 , 32 , 34 , 35 , 36 , 37 , 40 ].…”

“…The determination of thymol and carvacrol was usually performed on various types of electrode materials, including boron-doped diamond electrode (BDDE) [ 26 , 27 , 28 ], glassy carbon (GCE) [ 29 , 30 , 31 ] or modified with CeO 2 nanoparticle–decorated graphene hybrid film (CeO 2 /GN/GCE) [ 32 ], CeO 2 nanoparticles dispersed in Brij ® 35 [ 33 ], coimmobilized carboxylated multi-walled carbon nanotubes and surfactants (MWCNT-COOH-SDS/GCE) [ 34 ], multi-walled carbon nanotubes (MWNTs) [ 35 ], Nafion/multi-walled carbon nanotubes (Nafion/MWCNT/GCE) [ 36 ], uniform Ag@C@Ag core–shell structured nanocomposites [ 37 ] and other single-walled carbon nanotubes screen-printed electrode (SWCNT-SPE) [ 38 ], screen-printed electrode modified with La 2 O 3 /Co 3 O 4 nanocomposite [ 39 ], MnY nanozeolite modified carbon paste electrode (MnY/CPE) [ 40 ] and polyacrylamide embedded graphite molecular imprinted polymer electrode (PAM@G–MIP) [ 41 ]. The DPV technique was mainly used for THY and CAR determination, because it is characterized by the high sensitivity and good separation of the recorded peaks.…”

“…The voltammetric investigations were carried out in aqueous buffer solutions: phosphate [ 29 , 32 , 33 , 35 , 39 , 40 , 41 ], Britton-Robinson [ 26 , 34 ], acetate [ 27 , 28 ] or in alcohols [ 30 , 31 , 36 ].…”

Analytical Applications of Electrochemically Pretreated Boron‐Doped Diamond Electrodes

“…Interestingly, in the last decade or so, there were many reports of different analytical applications based on CPT‐BDDEs, but lacking comparisons with the performance of the APT or as‐grown electrode; the CPT may have been preceded or not by an APT. This direct, trustful use of CPT‐BDDEs is most probably based on the understanding that HT‐BDD surfaces are hydrophobic and thus might better interact with the investigated analyte, consequently resulting in a higher intensity of the current signal …”