Bioelectrocatalysis is a phenomenon concerned with biological catalysts, which accelerate the electrochemical reactions. Bioelectrocatalysis has been widely explored by the research community in various directions. Enzymes can catalyze different chemical reactions in living organisms by enzymes as the most important biological catalysts. These enzymatic biocatalysts are commercially available and commonly called enzyme electrodes. Electron transfer between the active center of the enzyme and the electrode can be performed either by direct electron transfer (DET) or by means of mediators (i.e. mediated electron transfer (MET)), which are discussed in details in the presented review. Therefore, different strategies have been used to increase the efficiency and stability of bioelectrocatalysis. In this review, different strategies of the bioelectrode designs have been discussed and the application of the common bioelectrodes used in the biosensors have been presented in the various fields. Moreover, a summary of the research status in the applications of bioelectrocatalysis in biosensors and biofuel cells was provided.
Migration of chemicals from plastic containers into drinks and liquids containing them, is supposed to be a hazardous phenomenon and results in many health problems. Sample preparation is of great importance due to trace amounts analysis of these compounds. In this research, dispersive liquid–liquid microextraction is applied for the extraction and preconcentration of the migrated compounds prior to their detection and determination by gas chromatography equipped with mass spectrometry or flame ionization detector. The method is on the basis of forming droplets of a water–immiscible organic solvent (extractant) into an aqueous phase by means of a disperser solvent. As a result, there would be a large contact area between the extractant and aqueous phase containing the analytes which boosts mass transfer. After centrifuging, the extractant is sedimented at the bottom of the aqueous phase and an aliquot of it is removed and injected into the separation system. Various experimental conditions which influence the extraction efficiency were optimized. Under the optimum conditions, the extraction recoveries were ranged from 52–63%. The relative standard deviations were ≤ 7.2% for intra– (n = 6) and inter–day (n = 4) precisions at a concentration of 20 µg L–1 of each analyte. The limits of detection were in the range of 0.18–0.38 µg L–1. Eventually the applicability of the proposed method for appraising the compounds migrated from the plastic containers was evaluated by analyzing the target compounds in different drinks and liquids stored in the plastic bottles.
In this study, an easy, fast, sensitive and accurate technique has been described for extraction and quantitative analysis of fluoxetine and propafenone using off-line coupling of ionic liquid–based dispersive liquid–liquid micro-extraction with high performance liquid chromatography. The effective extraction variables including: the ionic liquid volume, the type and volume of dispersive solvent, the pH, the extraction and centrifugation time, and the volume of diluent solvent have been investigated and optimized. The optimum chromatographic conditions were also obtained for the drugs determination. Under optimum conditions, the analytical curves were linear (r 0.999) within a wide concentration range (0.01–2.00 μg mL-1). Relative standard deviations (precision) and detection limits for both drugs have been smaller than 5% and 0.005 μg mL-1, respectively. The proposed method has been used successfully to detect and determine fluoxetine and propafenone in the capsule formulation and the spiked plasma samples; respectively, with the quantitative recovery results (94–97%).
The presented study describes the solvent extraction process of Zn(II) and Pb(II) from aqueous solutions by a cation exchanger extractant named bis(2-ethylhexyl)phosphoric acid (DEHPA). The results confirm that both of the extraction efficiency and extraction selectivity depend on the employed organic diluent. The applied extractant was selective towards zinc ions; this selectivity did not depend on the employed organic diluent. Keep in mind the possible interaction of the studied metal ions with the polyether compounds (PEGs) dissolved in the aqueous phase, the role of the presence of two PEGs with molecular masses 200 (PEG200) and 2000 (PEG2000) on the selectivity characteristics of the proposed extraction system was appraised. The evaluated PEGs play the role of masking agents by complexing the lead ions in the aqueous phase, while the zinc ions did not interact with them. These interactions result in the transposition of the extraction curves of lead as a function of pH, towards higher pH regions, whereas the extraction curves of zinc remained almost unchanged. By replacing the organic diluent (CCl4), by another one capable to dissolve the complexed lead ions with PEG200 (e.g. chloroform), a synergistic extraction was observed. This latter observation clearly showed the decisive impact of the employed solvent on the effect of the investigated PEGs to act as a masking or synergistic agent in the studied solvent extraction system.