Mihaela Buleandra

Rapid determination of total polyphenolic content in tea samples based on caffeic acid voltammetric behaviour on a disposable graphite electrode

The present paper describes the voltammetric behaviour and the quantitative determination of caffeic acid (CA) on a disposable pencil graphite electrode (PGE). The anodic peak current of CA recorded by differential pulse voltammetry (DPV) varies linearly with CA concentration in the range 1×10(-7)-3×10(-3) M. The detection and quantification limits were 8.83×10(-8) M and 2.94×10(-7) M caffeic acid, respectively. The mean recoveries of CA from Turkish green, white and black teas were 98.30%, 99.57% and 91.46%. For these three tea types the corresponding total polyphenolic contents (TPCs) evaluated by DPV on PGE were 35.81, 34.59 and 31.21 mg caffeic acid equivalent/g tea, respectively. These TPC values were in good accordance with those obtained by the Folin-Ciocalteu method. The developed DPV on PGE method constitutes a simple and inexpensive tool for the rapid assessment of TPC of tea samples.

Pencil Graphite Electrodes: A Versatile Tool in Electroanalysis

Due to their electrochemical and economical characteristics, pencil graphite electrodes (PGEs) gained in recent years a large applicability to the analysis of various types of inorganic and organic compounds from very different matrices. The electrode material of this type of working electrodes is constituted by the well-known and easy commercially available graphite pencil leads. Thus, PGEs are cheap and user-friendly and can be employed as disposable electrodes avoiding the time-consuming step of solid electrodes surface cleaning between measurements. When compared to other working electrodes PGEs present lower background currents, higher sensitivity, good reproducibility, and an adjustable electroactive surface area, permitting the analysis of low concentrations and small sample volumes without any deposition/preconcentration step. Therefore, this paper presents a detailed overview of the PGEs characteristics, designs and applications of bare, and electrochemically pretreated and chemically modified PGEs along with the corresponding performance characteristics like linear range and detection limit. Techniques used for bare or modified PGEs surface characterization are also reviewed.

Chemical Composition and Antipathogenic Activity of Artemisia annua Essential Oil from Romania.

The essential oil extracted by hydrodistillation from Romanian Artemisia annua aerial parts was characterized by GC/MS analysis, which allowed the identification of 94.64% of the total oil composition. The main components were camphor (17.74%), α‐pinene (9.66%), germacrene D (7.55%), 1,8‐cineole (7.24%), trans‐β‐caryophyllene (7.02%), and artemisia ketone (6.26%). The antimicrobial activity of this essential oil was evaluated by determining the following parameters: minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC), minimal fungicidal concentration (MFC), and minimal biofilm eradication concentration (MBEC). Moreover, the soluble virulence factors were quantified with different biochemical substrates incorporated in the culture media. The reference and resistant, clinical strains proved to be susceptible to the A. annua oil, with MICs ranging from 0.51 to 16.33 mg/ml. The tested essential oil also showed good antibiofilm activity, inhibiting both the initial stage of the microbial cell adhesion to the inert substratum and the preformed mature biofilm. When used at subinhibitory concentrations, the essential oil proved to inhibit the phenotypic expression of five soluble virulence factors (hemolysins, gelatinase, DNase, lipases, and lecithinases). Briefly, the present results showed that the A. annua essential oil contained antimicrobial compounds with selective activity on Gram‐positive and Gram‐negative bacterial strains as well as on yeast strains and which also interfere with the expression of cell‐associated and soluble virulence factors.

Voltammetric determination of B1 and B6 vitamins using a pencil graphite electrode

Due to the importance of B1 and B6 vitamins for human health it is useful to develop new cheap and rapid methods for their determination. Voltammetric behavior of these vitamins on a pencil graphite electrode was investigated using cyclic voltammetry in different media. Direct quantitative determination of the two vitamins, one in the presence of the other, was done by differential pulse voltammetry. Vitamin B1 was electroactive only in a NaOH solution generating two irreversible oxidation peaks; the first peak obtained at 250 mV is well-defined and was used in quantitative determinations. In case of vitamin B6, a well-defined oxidation peak was observed in all investigated supporting electrolytes except for HCl. The linear concentration ranges were 10−5–10−3 M for vitamin B1 in a NaOH solution and 5 × 10−6–10−3 M for vitamin B6 in an acetate buffer solution. The obtained detection limits were 5.34 × 10−6 M and 2.81 × 10−6 M for vitamin B1 and vitamin B6, respectively. The developed method is simple and rapid and it was successfully applied in the determination of the two vitamins in pharmaceuticals.

Cheap pencil graphite electrodes for rapid voltammetric determination of chlorogenic acid in dietary supplements

A disposable, cheap and easily available pencil graphite electrode (PGE) was used to develop, for the first time, a rapid voltammetric method for chlorogenic acid (CGA) determination. Cyclic voltammograms emphasised a quasi-reversible, diffusion controlled and pH dependent electrode process. Differential pulse voltammetry (DPV) applied to the anodic peak was used for the quantitative determination of CGA. The linear range, the limit of detection and the limit of quantification were 1 × 10−7 to 5 × 10−4 mol L−1 CGA, 7.14 × 10−8 mol L−1 CGA and 2.1 × 10−7 mol L−1 CGA, respectively, being similar to or even better than those reported in the literature. The developed DPV on PGE method was applied with good results to the quantitative determination of CGA in commercially available green coffee extract based dietary supplements. The results compared well with those obtained by the Folin–Ciocalteu method, a fact proved by the statistical analysis.

A Derivative Spectrometric Method for Hydroquinone Determination in the Presence of Kojic Acid, Glycolic Acid, and Ascorbic Acid

A new, simple, and sensitive spectrometric method was developed for hydroquinone (HQ) determination in the presence of other depigmenting agents (kojic acid (KA), glycolic acid (GA), and ascorbic acid (AA)), commonly introduced in skin lightening products. The method is based on the oxidation of the depigmenting agents by potassium dichromate in sulfuric acid medium and subsequent measurement of the amplitude of the first-order derivative absorption spectrum at 268 nm. By applying the zero-crossing method, at this wavelength, the oxidation products of KA, AA, and GA do not interfere in the indirect determination of HQ. Beer’s law was obeyed in the range of 0.22–22 μg·mL−1 HQ, with a detection limit of 0.07 μg·mL−1. The developed method was applied with good results for the first time to the rapid determination of HQ in binary, ternary, and quaternary mixtures, thus proving that it could represent an effective tool for various skin lightening products analyses.

Integrating Microwave-Assisted Extraction of Essential Oils and Polyphenols from Rosemary and Thyme Leaves

The extraction of essential oils (EOs) and polyphenols from rosemary and thyme has been done using an integrated process: microwave hydro-diffusion and gravity (MHG) for EOs and microwave-assisted extraction (MAE) for polyphenols. The innovative installation based on the MHG principle allows uniform microwave irradiation field due to a mechanical stirring and experiments done at low pressure. The results of quantitative analysis of the EOs extracted by MHG after 10 min were similar with those obtained by traditional methods (conventional hydro-distillation (CHD) and microwave-assisted hydro-distillation (MHD)) after 150 and 105 min, respectively. The specific energy for MHG was 5–15 times lower compared with these classical methods. The MHG extraction of EOs is also an effective method for plant material pretreatment before polyphenol extraction. Total phenolic content increased from 35 to 55 mg GAE/g DM for rosemary and from 23 to 38 mg GAE/g DM for thyme.

Chemical Composition of the Aerial Part and Fruits of Coreopsis tinctoria

Coreopsis tinctoria Nutt. from the Asteraceae family is an annual plant originating from North America and is widespread all over the world [1]. It is cultivated for both its ornamental and dyeing properties because of its bright yellow daisy-like flowers with maroon centers. Recently, this plant has been used to treat several disorders including diarrhea, internal pain and bleeding, to strengthen blood, to control diabetes, and also as an emetic [2–4]. A critical search of the literature reveals that there are few papers dedicated to the Coreopsis genus, and most of them focused on the chemical composition of the petals [5, 6]. So far, only one paper described a systematic study on the metabolic and biological properties of Coreopsis tinctoria [7]. Considered an alien species in Romania, this plant is cultivated mostly for its decorative value and has been classified among the new and rare plants in Romanian flora [8]. Therefore, because of its interesting properties, Coreopsis tinctoria cultivated in Romania was subjected to a systematic study regarding its chemical composition. Thus, this study reports on the identification of the major volatile compounds found in both the dried fruits and the aerial parts of this plant. Plant Material. Coreopsis tinctoria plants were cultivated in Bucharest and their aerial parts were collected during the flowering period, while fruits were collected at maturity. The plant material was air-dried and further stored in hermetically sealed dark paper bags to protect them from humidity and light. The Coreopsis tinctoria plant was authenticated by botanists from the Bucharest Botanical Garden based on available literature [9]. Headspace GC/MS Analysis. A quantity of 0.5 g of dry plant material (whether aerial part or fruits) was placed in a 20 mL headspace vial sealed with a silicone rubber septum and aluminum cap. Gas chromatography was carried out using a Thermo Electron apparatus fitted with a Triplus headspace automatic sampler. A DB-5MS capillary column (25 m 0.25 mm; 0.25 m film thickness) was used. The GC oven temperature program was: initial temperature 60 C (3 min) followed by an increase of 10 C/min up to 200 C (2 min) and then 12 C/min to the final temperature of 240 C (2 min). The carrier gas (helium) flow rate was 1 mL/min. The headspace temperature was kept at 80 C for 10 min prior to the injection of 500 L of the headspace gas into the column. The source and interface temperatures were 200 and 250 C, respectively. The detector operated in the electron impact mode (70 eV). Detection was performed in the range of m/z 35–300. The mass spectrometer was operated in the full-scan mode. All peaks of the chromatograms were analyzed using Xcalibur® software and the NIST 11 Mass Spectral Library to identify the corresponding compounds. An alkane standard solution for GC (C8–C20 in hexane) was used for retention index (RI) calculations [10]. The relative percent of individual components was calculated based on GC peak areas. GC/MS analysis of both the aerial part of the plant and its fruits revealed the presence of 27 volatile constituents (Table 1). Among them, some compounds were present only in the aerial part of the plant, such as -pinene, cis-ocimene, and trans-ocimene, while others were present only in the fruits, such as myrtenol, cis-carveol, and carvone. The quantitative analysis showed that there were few compounds present at a percentage higher than 10%, while most of them were below 2%.

Rapid voltammetric method for quinine determination in soft drinks

A novel voltammetric assay for quinine (QN) determination using an electrochemically pretreated pencil graphite electrode is described. The detection limit of QN was 2 × 10-7 M. The method possesses some obvious advantages including extreme simplicity, rapid response, and low cost.

Rapid Analysis of the Volatile Components of Gaillardia aristata and G. × grandiflora

Gaillardia belongs to the sunflower family (Asteraceae) and is native to North and South America. More than 30 species of it have been reported. Among the Gaillardia species there are some hybrids, the well known being one that blooms with reddish-purple flowers and named Gaillardia grandiflora Burgunder (Burgundy Blanket Flower) [1]. This hybrid is obtained from the annual Gaillardia pulchella and the perennial Gaillardia aristata. Even so, Gaillardia plants are widely cultivated for ornamental purposes, studies reported in the literature revealing interesting biological activity of several Gaillardia species. Thus, Gaillardia aristata Pursh exhibits antioxidant activities and possesses anti-inflammatory, antibiotic, and anticancer properties [2–4]. The other parent of the Burgunder hybrid, Gaillardia pulchella, is used in the treatment of gastroenteritis and skin disorders [5]. A critical review of the literature reveals that there are few papers describing the identification of volatile components of Gaillardia species. Thus, analysis of extracts of Gaillardia aristata and Gaillardia pulchella [4, 6] and a study of the essential oil obtained from flowers of Gaillardia aristata Pursh cultivated in Egypt [2] have been reported. No reference has been found for Burgunder species, either for essential oils or plants. Under these circumstances, this paper reports the results of a systematic study performed on Gaillardia aristata and Gaillardia grandiflora Burgunder in order to identify the major volatile compounds of these species. The method used was headspace gas chromatography – mass spectrometry (HS GC-MS), taking into account that headspace sampling has the advantage of being a rapid method that involves minimal sample manipulation. Plant Material. Plants of Gaillardia aristata Pursh and Gaillardia grandiflora Burgunder (voucher No. BUC 400642) were collected during the flowering period, and the plant material was air-dried and further stored in paper dark hermetic tight bags to protect them from humidity and light. The plants were authenticated by authors together with botanists from the Bucharest Botanical Garden. Headspace GC-MS Analysis. The headspace GC-MS instrumentation consisted of the Thermo Electron system, provided with a Triplus HS Autosampler. The 20 mL headspace vial containing a quantity of 0.5 g of dry plant was heated to 80 C for 10 min, and 500 L of the headspace gas was injected into the column. The GC-MS analyses were performed with a Focus GC chromatograph coupled with a Polaris Q ion trap mass detector. A DB-5MS capillary column (25 m 0.25 mm; 0.25 m film thickness) was used, and the carrier gas was helium at 1 mL/min. The GC oven temperature program was: initial temperature 60 C (3 min) followed by an increase of 10 C/min up to 200 C (2 min) and then 12 C/min to the final temperature of 240 C (2 min). The source and interface temperatures were 200 C and 250 C, respectively. The detector operated in the electron impact mode (70 eV). Detection was performed in the range of m/z 35–300. The mass spectrometer was operated in the full-scan mode. All peaks of the chromatograms were analyzed using Xcalibur® software and NIST 11 Mass Spectral Library in order to identify the corresponding compound. Alkane standard solution for GC (C8–C20 in hexane) was used for retention index (RI) calculation [7]. The relative percent of individual components was calculated based on GC peak areas.