Enhanced host–guest electrochemical recognition of herbicide MCPA using a b-cyclodextrin carbon nanotube sensor

An electrochemical sensor for the determination of the chlorophenoxy herbicide MCPA has been developed, based on a combination of multi-walled carbon nanotubes with incorporated b-cyclodextrin and a polyaniline film modified glassy carbon electrode. The proposed molecular host–guest recogni-tion based sensor has a high electrochemical sensitivity for the determination of MCPA. The electrochemical behaviour of MCPA at the chemically modified electrode was investigated in detail by cyclic voltammetry. The results indicate that the b-CD/MWCNT modified glassy carbon electrode exhibits efficient electrocatalytic oxidation of MCPA with high sensitivity, stability and lifetime. The analytical characteristics of this film were used for the quantitative determination of MCPA in natural waters. Cyclic voltammetry in phosphate buffer solution at pH 6.0, allowed the development of a method to determine MCPA, without any previous steps of extraction, clean-up, or derivatization, in the range of 10–100 mmol L-1, with a detection limit of 0.99 mmol L-1 in water. The results were statistically compared with those obtained through an established high-performance liquid chromato-graphy technique, no significant differences having been found between the two methods.info:eu-repo/semantics/publishedVersio

Measurement of pH. Definition, standards, and procedures (IUPAC Recommendations 2002)

The definition of a "primary method of measurement" [1] has permitted a full consideration of the definition of primary standards for pH, determined by a primary method (cell without transference, Harned cell), of the definition of secondary standards by secondary methods, and of the question whether pH, as a conventional quantity, can be incorporated within the internationally accepted system of measurement, the International System of Units (SI, Syst\ue8me International d'Unit\ue9s). This approach has enabled resolution of the previous compromise IUPAC 1985 Recommendations [2]. Furthermore, incorporation of the uncertainties for the primary method, and for all subsequent measurements, permits the uncertainties for all procedures to be linked to the primary standards by an unbroken chain of comparisons. Thus, a rational choice can be made by the analyst of the appropriate procedure to achieve the target uncertainty of sample pH. Accordingly, this document explains IUPAC recommended definitions, procedures, and terminology relating to pH measurements in dilute aqueous solutions in the temperature range 5-50 \ub0C. Details are given of the primary and secondary methods for measuring pH and the rationale for the assignment of pH values with appropriate uncertainties to selected primary and secondary substances

Electrochemical behaviour of cytochrome c at electrically heated microelectrodes

The structural changes in cytochrome c with temperature have been been followed using a recently developed electrically-heated microelectrode sensor. Differential pulse voltammetry was used to perform electrochemical measurements of cytochrome c oxidation at different temperatures at heated bare gold electrodes contained in phosphate-buffered cytochrome c solution at room temperature. The voltammetric response shows the onset of unfolding and a marked dependence of the signal on electrode temperature. This augurs well for applications of heated electrodes as local probes in the study of the temperature dependence of electron transfer processes of other redox proteins, avoiding problems of bulk deterioration.http://www.sciencedirect.com/science/article/B6TGX-3VKCCRN-D/1/171b8580ef00f2e0f90392182b57bde

Synthesis, characterization and influence of poly(brilliant green) on the performance of different electrode architectures based on carbon nanotubes and poly(3,4-ethylenedioxythiophene)

Brilliant green (BG), which belongs to the triphenylmethane family, has been electrochemically polymerised by cyclic voltammetry on bare carbon film electrodes (CFE) and for the first time on carbon nanotubes (CNTs) and poly(3,4-ethylenedioxythiophene) (PEDOT) modified CFE. The modified electrodes have been characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in order to establish the position importance and the individual role of each component (CNT, PEDOT and PBG) in the overall electrode performance. The analytical performances of different electrode architectures towards hydrogen peroxide detection allowed the choice of the best electrode configuration for further application of the newly developed electrodes for sensor and biosensor construction