Water-ethanol mixtures intended for specific purposes, such as bioethanol fuel, can be subject to national quality standards, including the measurement of pHe - a solvent-specific quantification of acidity. This work discusses the shortcomings of the use of pHe in these quality standards, including the lack of metrological traceability of pHe measurements made using combination pH electrodes calibrated using aqueous pH buffers. The feasibility of measuring the acidity of 50-50 wt% water-ethanol mixtures on a non-solvent-specific, unified pH scale, which is traceable to the conventional aqueous pH scale ( pH abs H 2 O ) is demonstrated. pH abs H 2 O measurements of buffered and un-buffered water-ethanol mixtures using two cell configurations, including the use of an ionic liquid salt bridge (ILSB), show good agreement. The cell configuration, consisting of a commercial glass (half-cell) electrode and a reference electrode incorporating an ILSB, can be readily adopted by measurement laboratories.
Within the past few decades, the application of light scattering techniques to a broad range of scientific disciplines has increased significantly, especially in the field of analytical chemistry. The resulting interest in and use of light scattering methods suggests the need for an easily understood introduction and review of material for those new to the method as well as for current users in need of a refresher. In many respects, the theory and its applications may appear so overwhelming for many studying the field for the first time, that they rarely can spend the time just needed to understand the basic measurements and their interpretations. A variety of applications in analytical chemistry especially have resulted in a greater understanding of many of the macromolecular processes themselves from molar mass distributions, to the macromolecular interactions responsible for aggregation processes, to determinations of structure and function. The use of such analytical processes to obtain a better understanding of nanoparticle structure and function has become almost universal.
In this study, cobalt nanoparticles (CoNPs) were synthesized and cobalt nanoparticles modified glassy carbon electrode (CoNPs/GCE) was prepared by drop coating the nanoparticles on glassy carbon electrode. After preparing polypyrrole modified glassy carbon electrode (PPy/GCE) using electropolymerization of pyrrole in LiClO4 solution, cobalt nanoparticles-polypyrrole composite modified glassy carbon electrode (CoNPs/PPy/GCE) was fabricated by drop coating the CoNPs on the PPy/GCE. Different characterization techniques such as scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, FTIR spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry were used to study the morphological structure and electrochemical behavior of the sensors. The results demonstrated that PPy chains interacted with CoNPs through donor-acceptor bonds. Among all the electrodes, CoNPs/PPy/GCE exhibited highest electroactive surface area and lowest electron transfer resistance towards phoxim. Under the optimal conditions, the sensor showed linear relationship between the reduction peak current and the concentration of phoxim in the range of 0.025 μM–12 μM with the detection limit as 4.5 nM. Besides, the composite electrode demonstrated excellent reproducibility, good stability and selectivity towards the possible interfering substances. All of these properties made CoNPs/PPy/GCE a suitable electrochemical sensor for the electrochemical determination of phoxim in water samples using square wave voltammetry.
Volatile solvents are excellent extraction media for liquid-liquid extractions. However, their use in supported liquid membranes (SLMs) is limited by their evaporation from SLM and thus poor SLM stability and they have never been considered truly useful for electromembrane extraction (EME). In this contribution, volatile solvents were systematically investigated as liquid membranes for EME and their extraction characteristics were comprehensively examined for the first time. A short plug of a water immiscible volatile solvent (a free liquid membrane (FLM)) was sandwiched between two aqueous plugs (donor and acceptor solutions) in a narrow-bore polymeric tubing. Evaporation of the volatile FLM was thus completely avoided and excellent stability of the phase interface was ensured. Suitability of volatile FLMs for EMEs was justified by m-EMEs of nortriptyline, haloperidol, loperamide and papaverine as model non-polar basic drugs. Extraction performance of m-EME through ethyl acetate was comparable or better to that through standard non-volatile EME solvents and a high extraction selectivity was achieved for nortriptyline and haloperidol extracted through chloroform. m-EMEs through the volatile FLMs were characterized by high extraction recoveries (62%-99% for standards and 40-89% for body fluids), low electric currents (10-1380 nA), no susceptibility to matrix ions and suitability for pretreatment of raw body fluids (human urine and serum). Resulting extracts were analysed by capillary electrophoresis with ultraviolet detection (CE/UV). Repeatability of the m-EME-CE/UV method was excellent with intra-day and inter-day RSD values 0.8-3.2% and 1.8-4.6%, respectively. Further experiments demonstrated additional advantages of volatile FLMs by nearly exhaustive m-EMEs of atenolol as the polar basic drug with no need for FLM modification by ionic carriers. The presented comprehensive examination of volatile solvents has broadened the range of liquid membranes suitable for EME and it is believed that this proof-of-concept study will stimulate further interest in a deeper investigation of volatile phase interfaces in EME. (C) 2021 Elsevier B.V. All rights reserved.
Microcystins (MCs) and nodularins (NODs) exhibit high structural variability, including modifications of the Adda (3S-amino-9S-methoxy-2S,6,8S-trimethyl-10-phenyldeca-4E,6E-dienoic acid) moiety. Variations include 9-O-desmethylAdda (DMAdda) and 9-O-acetylDMAdda (ADMAdda) which, unless targeted, may go undetected. Therefore, reference standards were prepared of [ADMAdda5]MCs and [DMAdda5]MCs, which were analyzed using multiple approaches. The cross-reactivities of the [DMAdda5]- and [ADMAdda5]MC standards were similar to that of MC-LR when analyzed with a protein phosphatase 2A (PP2A) inhibition assay, but were <0.25% when analyzed with an Adda enzyme-linked immunosorbent assay (ELISA). Oxidative cleavage experiments identified compounds that could be used in the analysis of total MCs/NODs in a similar fashion to the 2R-methyl-3S-methoxy-4-phenylbutanoic acid (MMPB) technique. Products from oxidative cleavage of both the 4,5- and 6,7-ene of Adda, DMAdda and ADMAdda were observed, and three oxidation products, one from each Adda variant, were chosen for analysis and applied to three field samples and a Nostoc culture. Results from the oxidative cleavage method for total Adda, DMAdda, and ADMAdda were similar to those from the Adda-ELISA, PP2A inhibition, and LC-MS/MS analyses, except for the Nostoc culture where the Adda-ELISA greatly underestimated microcystin levels. This oxidative cleavage method can be used for routine analysis of field samples and to assess the presence of the rarely reported, but toxic, DMAdda/ADMAdda-containing MCs and NODs.
