Deep eutectic solvents (DES) as green extraction media for antioxidants electrochemical quantification in extra-virgin olive oils.

A new electroanalytical method has been developed for the determination of polar antioxidant compounds in extra virgin olive oils. This method is based on the extraction of polar antioxidant compounds from extra-virgin olive oils by means of a deep eutectic solvent and their determination by a modified screen-printed electrode platform. The platform sensitivity was increased by modifying the working electrode with MWCNT and TiO2 nanoparticles as modifiers and Nafion as a binder. The platform showed very good sensitivity in detecting polar antioxidant compounds in extra-virgin olive oils in a fairly wide range of concentrations. The measurements were performed by using square wave voltammetry. The extraction was performed without using organic solvents, making the method environmentally friendly. The proposed method has been compared with a common spectrophotometric one, the results appeared in good agreement. The method is sufficiently easy and quick to be used for screening analyses of polar antioxidant compounds in extra-virgin olive oils on the field.

Biologically friendly room temperature ionic liquids and nanomaterials for the development of innovative enzymatic biosensors: Part II.

A newly modified electrode based on glassy carbon (GC) has been prepared and characterized electrochemically for application in electroanalytical chemistry. In particular, a GC screen-printed electrode (SPE) has been modified with nanostructures, namely multi-walled carbon nanotubes (MWCNTs), and TiO2 nanoparticles, and combined with a new generation of eco-friendly room-temperature ionic liquids (RTILs). The green RTILs here used are suitable for the immobilization of enzymes on the electrode surface and, additionally, facilitate the kinetics of electron transfer due to their intrinsic electrical conductivity. Upon evaluation of these newly modified electrodes we found an improvement in terms of electrochemically active area (Aea) with respect to the electrodes we previously reported. The modified SPEs were then used as substrates for the construction of two enzymatic biosensors for analytical applications: the first is an enzymatic biosensor based on alcohol dehydrogenase (ADH) for the analysis of ethyl alcohol; the second biosensor is based on lipase enzyme and has been tested for the analysis and the classification of Extra Virgin Olive Oil (EVOO). The performances of the here projected sensors appear comparable with biosensors having similar finalities. It is here envisaged that such a kind of electrodes could represent the starting tool for the construction and the definition of new portable devices for screening and field analyses.

Fast determination of biogenic amines in beverages by a core-shell particle column.

A fast and reliable HPLC method for the determination of 11 biogenic amines in beverages has been performed. After pre-column derivatization with dansyl-chloride a Kinetex C18 core-shell particle column (100 mm × 4.6 mm, 2.6 µm particle size) has been employed and the biogenic amines were identified and quantified in a total run time of 13 min with ultraviolet (UV) or fluorescence detection (FLD). Chromatographic conditions such as column temperature (kept at 50 °C), gradient elution and flow rate have been optimized and the method has been tested on red wine and fruit nectar. The proposed method is enhanced in terms of reduced analysis time and eluent consumption with respect of classical HPLC method as to be comparable to UHPLC methods. Green and cost-effective, this method can be used as a quality-control tool for routine quantitative analysis of biogenic amines in beverages for the average laboratory.

DNA-based biosensors for Hg(2+) determination by polythymine-methylene blue modified electrodes.

In this work we have developed a new electrochemical DNA-based biosensor for the selective determination of the Hg(2+) ion by the use of different electrodes modified with polythymine, bearing methylene blue, as redox probe, in 3' position. The determination of Hg(2+) can be employed with an excellent degree of selectivity by the use of DNA biosensors through the formation of the complex Thymine-Hg-Thymine (T-Hg-T): in fact, Hg(2+) tends to bind two thymines, generating a T-Hg-T complex with a formation constant higher than that one of the coupling Adenine-Thymine, which can be employed for a selective, fast and cost-effective Hg(2+) detection. The presence of the Hg(2+) in solution leads to the formation of T-Hg-T complex thus causing the "hairpin-like" folding of oligonucleotide, leading to an improved electronic exchange of methylene blue with the electrode surface due to the reduced distance and thus to an increase of the faradic current which is detected by means of square wave voltammetry (SWV). To test the feasibility of this kind of biosensor to be applied to the analysis of Hg(2+) we have developed several biosensors configuration by modifying the electrochemical sensor transducer: (a) Au electrode; (b) Au screen-printed electrode (SPE). The proposed system, allows the determination of Hg(2+) in the range 0.2-100 nM (0.05-20 ppb), with a sensitivity 0.327 µA/nM, LOD 0.1 nM (0.02 ppb), LOQ 0.2 nM (0.05 ppb) and RSD ≤4.3% when Au electrode is used as electrochemical transducer; on the other hand, in the case of Au SPE the linear range is 0.2-50 nM (0.05-10 ppb), with a sensitivity 0.285 µA/nM, while LOD and LOQ are the same as previously and RSD is ≤3.8%. This enabled the detection of mercury in real samples (waters and fishes) with good accuracy (recoveries 92-101% on waters and 92-107% on fishes, respectively) and reproducibility (RSD ≤9.6% for measurements on waters and ≤8.8% on fishes, respectively).

A microcalorimetric sensor for food and cosmetic analyses: l-Malic acid determination.

Enzymatic microcalorimetry has been successfully employed in the reliable determination of the l-malic acid concentration in some foods and cosmetic products. The l-malic acid concentration during the wine-making process is particularly useful in order to control the progress of the malo-lactic fermentation. Total acidity, taste and flavour characteristics of wine depend on the l-malic acid quantity still present. To point out the analytical methodology the dehydration process of l-malic acid, in the presence of Fumarase enzyme, has been used. The new method has been compared with a common spectrophotometric one. By the proposed calorimetric method the l-malic acid concentration in different types of food (white and red wines, fruits and soft beverages) has been determined. In some cosmetic products too the l-malic acid was quantified. The method outlined resulted simple, direct and reliable (good accuracy and precision), in particular it does not require any pre-treatment or clean up of the samples, save the dilution in buffer.

Interactions between gemini surfactants and polymers: thermodynamic studies.

Aqueous mixtures containing a homopolymer, poly(vinylpyrrolidone) (PVP), or a hydrophobically modified graft copolymer, HM-pullulan, (PULAU9, where 9 stands for the nominal substitution degree), and different Gemini surfactants have been investigated at 25.0 degrees C. A wide variety of experimental conditions were addressed by changing the amount of polymer and of surfactant. The Gemini surfactants were synthesized, purified, and characterized by routine methods. They differ from each other in polar head groups (two sulfonate-, two quaternary ammonium-, or two arginine-based groups), in alkyl chain length (11 or 12 carbon atoms), and in the distance between the polar head groups. The spacers consist of 2, 3, and 6 methylene units or 3 oxyethylene units. Surface activity and solution calorimetry measurements yield some physicochemical features inherent to micelle formation and polymer-surfactant interactions. The data are supported by ionic conductivity, detecting the critical thresholds and quantifying the modifications in binding associated with critical association (CAC) and micelle formation (CMC*). The Gibbs energy of transfer from the micelles to a polymer-binding site, DeltaGtrans, was evaluated from the CAC/CMC* ratios versus the amount of added polymer. A similar procedure determined the enthalpy of transfer, DeltaHtrans. DeltaGtrans decreases with added polymer, whereas DeltaHtrans becomes more negative on increasing the amount of polymer in the medium. According to the selected data presented here, cationic Geminis do not interact with PVP, while significant interactions have been observed in other surfactants. In mixtures with PULAU9, the interaction is significant for all Geminis. This effect is due to interactions between the surfactants and the hydrophobic alkyl groups on the main polymer chain. The pendent groups facing away from the polysaccharide chain act as binding sites for aggregates onto such polymers.

Lichen-based biosensor for the determination of benzene and 2-chlorophenol: microcalorimetric and amperometric investigations.

Preliminary microcalorimetric studies have been performed to analyse the response of a whole epiphytic lichen tissue (Evernia prunastri) to 2-chlorophenol (2Cl-phi), a pollutant of oil mill waste-water, in order to evaluate whether the tissue might be used to assess the toxic characteristics of polluted waters. The obtained results (lichen viability expressed in hours, enthalpy variations for the 2Cl-phi/lichen interactions) were used to create a lichen-based biosensor that uses an amperometric oxygen electrode (a Clark electrode) as a transducer. The lichen catalyses aromatic ring cleavage (via pyrocatechase enzymes present in the lichen), and transforms aromatic substances like 2Cl-phi into muconic acid (C6H6O4). Following a full electroanalytical characterisation, the performance of the proposed lichen biosensor was compared to that of a biosensor based on Pseudomonas putida cells, which was originally constructed to monitor benzene in different matrices (water, air, petrol and oil) and was tested in our laboratory previously.

Simultaneous quantitation of free and conjugated phytoestrogens in Leguminosae by liquid chromatography-tandem mass spectrometry.

Phytoestrogens are diphenolic compounds that are present in several edible plants and are particularly abundant in soybeans. Because of their estrogenical, antriestrogenical, anticarcinogenic and antioxidant activities in animal and humans, they became of great interest. Dietary factors are considered important in determination of risks, in fact, studies have revealed beneficial or protective effects of the consumption of vegetables, in particular soy and soybean products. So that in the present paper the simultaneous determination of eight isoflavones and coumestrol in vegetables is reported. The quantitative analysis has been made by means of LC separation combined with tandem mass spectrometry. In particular, a new simple and fast extraction methodology and a clean-up, based on cold aided de-fatting, is proposed. Method performance was evaluated by comparison with a reference procedure. The developed procedure was then used for a survey of phytoestrogens concentration in some selected vegetables.