Subtle adjustment of the cyclic potential on electro-activated glassy carbon electrodes for sensitive sensing of methyl parathion

Facile electro-activated glassy carbon electrodes (e-GCEs), which are prepared in electrolyte solution with a certain potential for a few seconds, have been verified to improve analytical performance toward not a few electro-active molecules recently. Nevertheless, how and why the potential plays an important role is not clear, and has even not received enough consideration. In this paper, we found that the mode and the range of applied potential significantly impacted the sensitivity of methyl parathion (MP), which is a typical pesticide with the electro-active group of -NO2. Compared with constant potential, the e-GCE with cyclic potential provided a much more stable baseline during MP detection. Additionally, the electro-oxidation peak current of MP at around -0.1 V on it was higher than another changeable potential (constant current). What's more interesting, with cyclic potential for 50 segments from -2 to 1.5 V, the peak current value increased by 30 times in comparison with a bare GCE, but only 2 times from -2 to 1 V. Then after systematic investigation including structures of the electrode surface and functional groups, we speculated that the produced group of O-CO in the process of activation and remaining groups of C-O and CO on the bare GCE surface are beneficial for adsorbing MP molecules leading to enhanced peak current. Employing the proposed e-GCE, the limit of detection of MP reached 0.015 μM and the reproducibility was perfect. This work elucidates the potent impact of electro-activation potential parameters on electroanalysis behaviors.

Helically aligned fused carbon hollow nanospheres with chiral discrimination ability

While the functions of carbon materials with precisely controlled nanostructures have been reported in many studies, their chiral discriminating abilities have not been reported yet. Herein, chiral discrimination is achieved using helical carbon materials devoid of chiral attachments. A Fe₃O₄ nanoparticle template with ethyl cellulose (carbon source) is self-assembled on dispersed multiwalled carbon nanotubes (MWCNTs) fixed in a lamellar structure, with helical nanoparticle alignment induced by the addition of a binaphthyl derivative. Carbonization followed by template removal produces helically aligned fused carbon hollow nanospheres (CHNSs) with no chiral molecules left. Helicity is confirmed using vacuum-ultraviolet circular dichroism spectroscopy. Chiral discrimination, as revealed by the electrochemical reactions of binaphthol and a chiral ferrocene derivative in aqueous and nonaqueous electrolytes, respectively, is attributable to the chiral space formed between the CHNS and MWCNT surfaces.

Ultra-sensitive and selective determination of a phenolic food additive using protein capped gold nanoclusters: a dual in-line fluorometric and colorimetric sensing probe

The application of red luminescence BSA-AuNCs towards the selective determination of food additive tert-butylhydroquinone (TBHQ) was demonstrated by both fluorometric and colorimetric methods.

Selective Electrochemical versus Chemical Oxidation of Bulky Phenol

The electrochemical oxidation of selected tert-butylated phenols 2,6-di-tert-butyl-4-methylphenol (1), 2,6-di-tert-butylphenol (2), 2,4,6-tri-tert-butylphenol (3), 2-tert-butylphenol (4), and 4-tert-butylphenol (5) was studied in an aprotic environment using cyclic voltammetry, square-wave voltammetry, and UV-vis spectroscopy. All compounds exhibited irreversible oxidation of the corresponding phenol or phenolate ion. Compound 2 was selectively electrochemically oxidized, while other phenol analogues underwent mostly chemical oxidation. The electrochemical oxidation of 2 produced a highly absorbing product, 3,5,3',5'-tetra-tert-butyl-4,4'-diphenoquinone, which was characterized by X-ray crystal diffraction. The electrochemical oxidation was monitored as a function of electrochemical parameters and concentration. Experimental and theoretical data indicated that the steric hindrance, phenoxyl radical stability, and hydrogen bonding influenced the outcome of the electrochemical oxidation. The absence of the substituent at the para position and the presence of the bulky substituents at ortho positions were structural and electrostatic requirements for the selective electrochemical oxidation.

Highly Sensitive and Selective Determination of Tertiary Butylhydroquinone in Edible Oils by Competitive Reaction Induced "On-Off-On" Fluorescent Switch

As one of most common synthetic phenolic antioxidants, tertiary butylhydroquinone (TBHQ) has received increasing attention due to the potential risk for liver damage and carcinogenesis. Herein, a simple and rapid fluorescent switchable methodology was developed for highly selective and sensitive determination of TBHQ by utilizing the competitive interaction between the photoinduced electron transfer (PET) effect of carbon dots (CDs)/Fe(III) ions and the complexation reaction of TBHQ/Fe(III) ions. This novel fluorescent switchable sensing platform allows determining TBHQ in a wider range from 0.5 to 80 μg mL(-1) with a low detection limit of 0.01 μg mL(-1). Furthermore, high specificity and good accuracy with recoveries ranging from 94.29 to 105.82% in spiked edible oil samples are obtained with the present method, confirming its applicability for the trace detection of TBHQ in a complex food matrix. Thus, the present method provides a novel and effective fluorescent approach for rapid and specific screening of TBHQ in common products, which is beneficial for monitoring and reducing the risk of TBHQ overuse during food storage.

Electrochemical Methods for Total Antioxidant Capacity and its Main Contributors Determination: A review

Backround: The present review focuses on electrochemical methods for antioxidant capacity and its main contributors assessment. The main reactive oxygen species, responsible for low density lipoprotein oxidation, and their reactivity are reminded. The role of antioxidants in counteracting the factors leading to oxidative stress-related degenerative diseases occurence, is then discussed. Antioxidants can scavenge free radicals, can chelate pro-oxidative metal ions, or quench singlet oxygen. When endogenous factors (uric acid, bilirubin, albumin, metallothioneins, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione-S-transferase) cannot accomplish their protective role against reactive oxygen species, the intervention of exogenous antioxidants (vitamin C, tocopherols, flavonoids, carotenoids etc) is required, as intake from food, as nutritional supplements or as pharmaceutical products.

Literature study: The main advantages of electrochemical methods with respect to traditional, more laborious instrumental techniques are described: sensitivity, rapidity, simplicity of the applied analytical procedure which does not require complicated sample pre-treatment etc.

The paper reviews minutiously the voltammetric, amperometric, biamperometric, potentiometric and coulometric methods for total antioxidant capacity estimation. For each method presented, the electroactivity and the mechanism of electro-oxidation of antioxidant molecules at various electrodes, as well as the influences on the electroactive properties are discussed. The characteristics of the developed methods are viewed from the perspective of the antioxidant molecule structure influence, as well as from the importance of electrode material and/or surface groups standpoint.

The antioxidant molecule-electrode surface interaction, the detection system chosen, the use of modifiers, as well as the nature of the analysed matrix are the factors discussed, which influence the performances of the studied electrochemical techniques.

Conclusions: The electrochemical methods reviewed in this paper allow the successful determination of the total antioxidant capacity and of its main contributors in various media: foodstuffs and beverages, biological fluids, pharmaceuticals. The advantages and disadvantages of the electrochemical methods applied to antioxidant content and antioxidant activity assay are treated and interpreted, in the case of various analysed matrixes. Combining advanced materials with classical electrode construction, provides viable results and can constitute an alternative for the future.

Stability of biodiesel, its improvement and the effect of antioxidant treated blends on engine performance and emission

Biodiesel consists of long chain fatty acid esters derived from vegetable oils, animal fats, and used oils.