Multivariate optimization of hydrodistillation-headspace solvent microextraction of thymol and carvacrol from Thymus transcaspicus

Solvent-Focused Gas Chromatographic Determination of Thymol and Carvacrol Using Ultrasound-Assisted Dispersive Liquid-Liquid Microextraction through Solidifying Floating Organic Droplets (USA-DLLME-SFO)

An ultrasound-assisted dispersive liquid-liquid microextraction by solidifying floating organic droplets, coupled to a form of temperature-programmed gas chromatography flame ionization detection, has been developed for the extraction and determination of thymol and carvacrol. This method utilizes undecanol as the extraction solvent, offering advantages such as facilitating phase transfer through solidification and enhancing solvent-focusing efficiency. The optimal gas chromatography conditions include a sample injection volume of 0.2 µL, a split ratio of 1:10, and a flow rate of 0.7 mL min-1. The extraction conditions entail an extraction solvent volume of 20 µL, a disperser solvent (acetone) volume of 500 µL, pH 7.0, 7.0% NaCl (3.5 M), a sample volume of 5.0 mL, an ultrasound duration of 10 min, and a centrifuge time of 7.5 min (800 rpm). These conditions enable the achievement of a high and reasonable linear range of 3.5 to 70. 0 μg mL-1 for both thymol and carvacrol. The detection limits are found to be 0.95 and 0.89 μg mL-1, respectively, for thymol and carvacrol. The obtained relative standard deviations, 2.7% for thymol and 2.6% for carvacrol, demonstrate acceptable precision for the purpose of quantitative analysis.

Electrode Based on the MWCNTs and Electropolymerized Thymolphthalein for the Voltammetric Determination of Total Isopropylmethylphenols in Spices

Isopropylmethylphenols, namely thymol and carvacrol, are natural phenolic monoterpenoids with a wide spectrum of bioactivity making them applicable in the cosmetic, pharmaceutical, and food industry. The dose-dependent antioxidant properties of isopropylmethylphenols require their quantification in real samples. Glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and electropolymerized thymolphthalein has been developed for the sensitive quantification of isopropylmethylphenols. Conditions of thymolphthalein electropolymerization (monomer concentration, number of cycles, and electrolysis parameters) providing the best response to thymol have been found. Scanning electron microscopy and electrochemical methods confirm the effectivity of the electrode developed. The linear dynamic ranges of 0.050-25 and 25-100 µM for thymol and 0.10-10 and 10-100 µM for carvacrol with detection limits of 0.037 and 0.063 µM, respectively, have been achieved in differential pulse mode in Britton-Robinson buffer pH 2.0. The selectivity of the isopropylmethylphenols response in the presence of typical interferences (inorganic ions, saccharides, ascorbic acid) and other phenolics (caffeic, chlorogenic, gallic and rosmarinic acids, and quercetin) is a significant advantage over other electrochemical methods. The electrode has been used in the analysis of oregano and thyme spices. Total isopropylmethylphenols contents have been evaluated after a single sonication-assisted extraction with methanol.

Synthesis of a new magnetic metal organic framework based on nickel for extraction of carvacrol and thymol in thymus and savory samples and analyzed with gas chromatography

The present research aims at reporting a new sorbent, a magnetic nano scale metal-organic framework (MOF), based on nickel acetate and 6-phenyl-1,3,5-triazine-2,4-diamine. The prepared sorbent was used to extract carvacrol and thymol using an ultrasonic-assisted dispersive micro solid phase extraction (UA-DμSPE) method. The structure of the metal organic framework was studied by applying scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectrometry (EDS), and vibrating sample magnetometer (VSM). The effects of various parameters such as ionic strength of sample solution, amount of sorbent (mg), volume of eluent solvent (μL), vortex and ultrasonic times (min) were optimized. Under optimal conditions, the analytes resulted in determination coefficients (R ²) of 0.9985 and 0.9967 in the concentration range 0.01-2 μg mL^-1, and in limits of detection of 0.0025 and 0.0028 μg mL^-1. Significantly, this method can be successfully applied in order to determine the target analytes in spiked real samples. Notably, the relative mean recoveries range from 94.5 to 105.7%.

Second-order electrochemical data generation to quantify carvacrol in oregano essential oils

A novel analytical method using voltammetric second-order modeling based on multivariate curve resolution-alternating least-square (MCR-ALS) is presented for the first time for the quantitation of carvacrol (CAR) in oregano essential oils (OEO). The second-order cyclic voltammetry data were generated on the basis that CAR shows a diffusional system. Thus, the scan rate (v) was used as a second instrumental mode and cyclic voltammograms at different v were acquired for a single sample, generating the second-order data. CAR determination was performed in presence of thymol, included as a potential interferent. Results demonstrated that MCR-ALS successfully exploited the second-order advantage and the recoveries were not statistically different than 100%. The limits of detection and quantitation were estimated using the MCR-ALS which were 6.27 × 10^-5°mol°L^-1°and 1.90 × 10^-4°mol L^-1, respectively. Finally, the developed methodology was implemented to quantify of CAR in OEO samples.

Highly effective pre-concentration of thymol and carvacrol using nano-sized magnetic molecularly imprinted polymer based on experimental design optimization and their trace determination in summer savoury, Origanum majorana and Origanum vulgare extracts

To ascertain thymol and carvacrol in pharmaceutical syrups, a valid and effective magnetic molecular imprinted polymer dispersive solid phase microextraction (MMIP-DSPME) process was developed in this study, which was in combination with a high performance liquid chromatography-ultra violet (HPLC-UV) technique for the assessment of thymol and carvacrol separation and pre-concentration. Contact time, eluent kind and volume, pH, the mass of the MMIP were all taken into consideration as key factors. Design expert and multi-objective response surface methodology (RSM) were used to optimize these variables. The mass of the MMIP, sample pH, eluent kind, time of sorption, the volume of eluent, and time of elution were 10 mg, 6, acetonitrile, 28 min, 200 µL, and 5.5 min, respectively, for the maximum extraction recovery of the analytes. The limit of detection (LOD) was 0.042 ng mL^-1 at the optimal conditions, while the value for the limit of quantification (LOQ) was 0.140 ng mL^-1. At the optimized conditions for thymol and carvacrol, the suggested MMIP sorbent had sorption capacities of 64.1 and 72.6 mg g^-1, respectively. Furthermore, for triplicate measurements, the linear dynamic range (LDR) was 0.40-5000 ng mL^-1, and the method's accuracy (RSD %) was 6.26%. The saturation magnetization for the MMIP was 19.0 emu g^-1 obtained by VSM, allowing the sorbent to be separated quickly. The sorption experiments confirmed the large sorption capacity of the MMIP for thymol and carvacrol, as well as its homogeneous binding sites. The extraction recovery for thymol and carvacrol was 96.9-103.8% and 96.6-105.4%, respectively, at all spiked amounts (20, 100, 200, and 500 ng mL^-1). The findings of seven desorption-regeneration cycles using MMIP demonstrated the high stability of the sorbent. The MMIP revealed a particular behavior of sorption for thymol and carvacrol, implying a selective, simple, effective, and flexible analytical method.

Ultrasound Assisted Dispersive Solid Phase Microextraction of Thymol and Carvacrol in Pharmaceutical Products Using Graphene Oxide as an Adsorbent Prior to Analysis by High Performance Liquid Chromatography

Background:

Thymol and carvacrol are the most important dietary constituents in thyme species. These two active compounds are used for the standardization of pharmaceutical compounds.

Objective:

In this work, a simple and reliable ultrasonic assisted dispersive solid phase microextraction method (USA-DSPME) coupled with high performance liquid chromatography-ultra violet detection system was developed to determine thymol and carvacrol in pharmaceutical syrups. The efficiency of SPME sorbent was examined through several sorbents and finally Graphene Oxide (GO) was applied for extraction of the analytes. Method: The efficiency of GO was compared with three reduced forms of GO adsorbents as well. Several effective factors on the extraction performance were investigated.

Results:

Under the optimized conditions for the GO sorbent, inter and intra-day relative standard deviations (RSDs, n = 3) and the Limits of Detections (LODs) were lower than 5.0% and 0.02 μg/ml, respectively. Moreover, good linear ranges were observed in wide concentration ranges with R-squared larger than 0.9961 for both thymol and carvacrol.

Conclusion:

The present method is reliable and simple for determination of carvacrol and thymol in pharmaceutical products.

Ultrasound combined with manganese-oxide nanoparticles loaded on activated carbon for extraction and pre-concentration of thymol and carvacrol in methanolic extracts of Thymus daenensis, Salvia officinalis, Stachys pilifera, Satureja khuzistanica, and mentha, and water samples

A dispersive micro solid-phase extraction (DMSPE) technique was developed using manganese-oxide nanoparticles loaded on activated carbon (Mn₃O₄-NPs-AC) as an effective sorbent combined with ultrasound for the extraction and determination of a trace amount of thymol and carvacrol in methanolic extracts of Thymus daenensis, Salvia officinalis, Stachys pilifera, Satureja khuzistanica and mentha, and water samples.

Development of an electrochemical method to determine phenolic monoterpenes in essential oils

A simple, rapid and non-expensive method is proposed to determine phenolic monoterpenes such as thymol and carvacrol in essential oils of thyme and oregano. The linear sweep voltammetry based on glassy carbon electrodes was the electrochemical technique used. Thymol and carvacrol have one main oxidation peak in non-aqueous media centered at about 1.3 V vs. Ag/AgCl. The electron transfer process is mainly diffusion controlled. The calibration plots generated using the commercial standards of thymol and carvacrol were used to estimate the total content in real samples. The calibration plots were linear in the concentration range from 8.5 × 10^-5 to 1.3 × 10^-3 mol L^-1 and 7.9 × 10^-5 to 1.2 × 10^-3 mol L^-1 for thymol and carvacrol, respectively. Results obtained with the electrochemical method are in good agreement with those of the official method (gas chromatography). In addition, the analytical procedure does not require previous preparation of the sample or modification of the electrode surface. The electrochemical technique used is very simple to apply. Under these conditions, the methodology proposed is a good, simple and fast option to perform a quality control of essential oils.

Synthesis and characterization of MIL-101(Cr) intercalated by polyaniline composite, doped with silica nanoparticles and its evaluation as an efficient solid-phase extraction sorbent

A metal-organic framework/polyaniline composite was synthesized and doped with silica nanoparticles. The structure and morphology of the composite were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy. It was packed inside a cartridge and evaluated for the solid-phase extraction of thymol and carvacrol, followed by gas chromatography with flame ionization detection measurement. The influence of the important experimental variables on the efficiency of the proposed method, including pH, ionic strength, volume of sample solution and type, and volume of eluent were studied and optimized. Under the optimal conditions, the relative standard deviations were found to be 3.8 and 9.8% for thymol and carvacrol, respectively, and the corresponding limits of detection were 0.1 and 1.0 ng/mL. The linear dynamic ranges for the calibration curves of the analytes were 10-10000 ng/mL, with determination coefficients (R² ) > 0.993. The limits of quantifications were found to be 0.01 and 0.5 μg/mL, for thymol and carvacrol, respectively. The prepared nanocomposite sorbent was applied successfully to the extraction and determination of thymol and carvacrol in Lamiaceae plant extracts and a honey sample, with relative recoveries in the range of 90.28-122.0%.

Maghemite nanoparticle-decorated hollow fiber electromembrane extraction combined with dispersive liquid-liquid microextraction for determination of thymol from Carum copticum

BACKGROUND

A novel technique using maghemite nanoparticle-decorated hollow fibers to assist electromembrane extraction is proposed. Electromembrane extraction combined with dispersive liquid-liquid microextraction (EME-DLLME) was applied for the extraction of thymol from Carum copticum, followed by gas chromatography with flame ionization detection (GC-FID).

RESULTS

The use of maghemite nanoparticle-decorated hollow fibers was found to improve the extraction efficiency of thymol significantly. Important operational parameters, including pH of acceptor phase, extraction time, voltage and temperature, were investigated and optimized. At the optimal conditions, linearity in the range 4-1800 µg L^-1 with a determination coefficient of 0.9996 was obtained. The limit of detection was 0.11 µg L^-1 (S/N = 3) and the pre-concentration factor was 200. The intra- and inter-day precision was 5.9 and 2.2% respectively. The intra- and inter-day accuracy was higher than 93.6%.

CONCLUSION

The results indicated that EME-DLLME/GC-FID is a useful technique for the extraction and determination of thymol in C copticum. © 2016 Society of Chemical Industry.

Ultrasound assisted microextraction-nano material solid phase dispersion for extraction and determination of thymol and carvacrol in pharmaceutical samples: experimental design methodology

In the present study, for the first time, a new extraction method based on "ultrasound assisted microextraction-nanomaterial solid phase dispersion (UAME-NMSPD)" was developed to preconcentrate the low quantity of thymol and carvacrol in pharmaceutical samples prior to their HPLC-UV separation/determination. The analytes were accumulated on nickel sulfide nanomaterial loaded on activated carbon (NiS-NP-AC) that with more detail identified by XRD, FESEM and UV-vis technique. Central composite design (CCD) combined with desirability function (DF) was used to search for optimum operational conditions. Working under optimum conditions specified as: 10 min ultrasonic time, pH 3, 0.011 g of adsorbent and 600 μL extraction solvent) permit achievement of high and reasonable linear range over 0.005-2.0 μg mL(-1) (r(2)>0.9993) with LOD of thymol and carvacrol as 0.23 and 0.21 μg L(-1), respectively. The relative standard deviations (RSDs) were less than 4.93% (n=3).

Single drop microextraction--development, applications and future trends

Single drop microextraction (SDME) has emerged over the last 10-15 years as one of the simplest and most easily implemented forms of micro-scale sample cleanup and preconcentration. In the most common arrangement, an ordinary chromatography syringe is used to suspend microliter quantities of extracting solvent either directly immersed in the sample, or in the headspace above the sample. The same syringe is then used to introduce the solvent and extracted analytes into the chromatography system for identification and/or quantitation. This review article summarizes the historical development and various modes of the technique, some theoretical and practical aspects, recent trends and selected applications.