Study of adsorption of methylene blue and new methylene blue in liquid-solid interface by slab optical waveguide spectroscopy

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid–solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. Effect of pH on adsorption on MB and NMB was investigated. Binding rate constant analysis showed that both MB and NMB on bare SOWG demonstrates larger association constants than those on ODS-SOWG. Interactions of MB and NMB on bare SOWG and ODS-SOWG were analyzed by molecular mechanics calculation method. The binding energy change was in the following order: E_NMB–bare > E_MB–bare > E_NMB–ODS > E_MB–ODS.     

Simultaneous determination of methylene blue and new methylene blue by slab optical waveguide spectroscopy and artificial neural networks

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid-solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. The simultaneous determinations of both MB and NMB were explored by flow injection SOWG spectrophotometric analysis and artificial neural networks (ANNs) for the first time. Concentrations of MB and NMB were estimated simultaneously with the ANNs. Results obtained with SOWG were compared with those got by conventional UV-visible spectrophotometry.     

A sub-second, time-resolved, linear dichroism measurement system for visible attenuated total reflection spectroscopy with a slab optical waveguide

A sub-second, time-resolved, linear dichroism (LD) measurement system was constructed, fitted with a slab optical waveguide (SOWG), and utilized to observe the adsorption process of methylene blue (MB) onto silica surfaces. In the system, a semiconductor laser (670 nm) was used as the light source and the out-coupled beam from the SOWG was split by a polarizing beam splitter into two polarized beams (TE and TM modes) to allow sequential linear dichroic ratio data to be obtained; the acquisition rate was 11 data sets per second. For an MB solution that contained no sodium dodecylbenzenesulfonate (DBS), in contact with a bare silica surface, a clear decrease occurred in the average orientation angle of adsorbed MB in the initial stages of the adsorption process. This result may correspond to a change in the chemical form of MB from monomer to dimer.     

In situ monitoring of the H concentration change near an electrode surface through electrolysis using slab optical waveguide pH sensor

The H⁺ concentration change was monitored near an electrode surface through an electrolysis using a slab optical waveguide technique. Indium tin oxide transparent electrode modified by porous insulating polymer to which methyl red was covalently immobilized was used as a guiding layer, and the absorbance change of the polymer film was monitored. H⁺ generation at the vicinity of the electrode through the oxidation of ascorbic acid could be monitored by this technique.     

A non-primitive model for the electrode electrolyte interface based on the Percus–Yevick theory. Analysis of the different molecular sizes, ion valences and electrolyte concentrations

The electrode electrolyte interface is modelled by a mixture of charged and dipolar hard spheres against a planar, charged hard wall. A mean field theory is used to describe the coulombic interactions while steric effects are given by the Percus–Yevick theory. The underlying Percus–Yevick theory for three uncharged species against a planar wall is derived by using the standard method developed by Henderson et al. (D. Henderson, F.F. Abraham, J.A. Barker, Mol. Phys., 31 (1976) 1291) and compared with Monte-Carlo simulations. Although the Percus–Yevick theory has shortcomings, the theory provides an estimate of how the high density of the solvent influences the structural and thermodynamic properties. Consideration of the solvent molecules introduces oscillations in the density distribution of the ions and solvent while the different molecular sizes and ion valences lead to an asymmetry in the differential capacitance.     

Electrical probing of endothelial cell behaviour on a fibronectin/polystyrene/thiol/gold electrode by Faradaic electrochemical impedance spectroscopy (EIS)

The electrochemical impedance spectroscopy (EIS) technique has been shown to be an effective tool for monitoring endothelial cell behaviour on a multilayer functionalised gold electrode. Polystyrene, a reproducible model substrate, is deposited as a thin layer on a thiol functionalised gold electrode. Fibronectin, a protein promoting endothelial cell adhesion, is then adsorbed on the polystyrene surface. The different steps of this multilayer assembly are characterized by Faradaic impedance. The charge transfer resistance and the capacitance for the total layer are modified at each step according to the electrical properties of each layer. This gives the endothelial cells' electrical state in terms of its resistive and capacitive properties. In this study, the endothelial cell layer presents a specific charge transfer resistance equal to 1.55 kOmega cm(2) with no large defects in the cell layer, and a specific capacitance equal to few microF cm(-2) explained by the existence of pseudopods. These electrical properties are correlated to the endothelial cell viability, adhesion and cytoskeleton organization.     

Investigations on novel electrolytes,solvents and SEI additives for use in lithium-ion batteries: Systematic electrochemical characterization and detailed analysis by spectroscopic methods

Electrolyte solutions have vital function in lithium-ion batteries. Due to their modular composition, there is a broad variety of electrolyte component combinations. In this work, we present electrochemical results on newly investigated electrolyte solution components. The standard electrolyte salt in commercial batteries, LIPF₆, was replaced by new imide and sulfonate anion based salts, with enhanced stability. The use of propylene carbonate was enabled by the application of new SEI forming electrolyte additives. Electrolyte solvents, such as adiponitrile and γ-butyrolactone were investigated in combination with LiBF₄ as electrolyte salt. In order to evaluate these materials, various electrochemical techniques like galvanostatic cycling, conductivity and electrochemical stability window detection, cyclic voltammetry, etc. were applied. Furthermore, the electrode/electrolyte interfaces and interphases were studied via spectroscopic and spectrometric techniques.     

Design and application of a novel integrated electrochemical hydride generation cell for the determination of arsenic in seaweeds by atomic fluorescence spectrometry

An integrated electrochemical hydride generation cell, mainly composed of three components (a gas liquid separator, a graphite tube cathode and a reticulate Pt wire anode), was laboratory constructed and employed for the detection of arsenic by coupling to atomic fluorescence spectrometry. This integrated cell was free of ion-exchange membrane and individual anolyte, with the virtues of low-cost, easy assembly and environmental-friendly. Using flow injection mode, the sample throughput could come to 120 h⁻¹ attributed to the small dimension of the cathode chamber. The operating conditions for the electrochemical hydride generation of arsenic were investigated in detail and the potential interferences from oxygen or various ions were also evaluated. Under the optimized conditions, no obvious oxygen quenching effects were observed. The limit of detection of As (III) for the sample blank solution was 0.2 ng mL⁻¹ (3σ) and the relative standard deviation was 3.1% for nine consecutive measurements of 5 ng mL⁻¹ As (III) standard solution. The calibration curve was linear up to 100 ng mL⁻¹. The accuracy of the method was verified by the determination of arsenic in the reference materials GBW08517 (Laminaria Japonica Aresch) and GBW10023 (Porphyra crispata) and the developed method was successfully applied to determine trace amounts of arsenic in edible seaweeds.     

Fabrication of a novel electrochemical sensor based on tin disulfide/multi-walled carbon nanotunbes-modified electrode for rutin determination in natural vegetation

A tin disulfide and multi-walled carbon nanotube (SnS₂/CNTs) electrochemical sensor was constructed for the sensitive and selective determination of rutin in plants. Tin disulfide nanoflowers with various particle sizes were prepared by controlling the reaction time and composited with multi-walled CNTs. The morphology, crystal structure, and chemical composition of these SnS₂/CNTs composites were characterized using XRD, XPS, and SEM-EDS. Results illustrated that the SnS₂/CNTs had a large specific surface area, good conductivity, and remarkable electrocatalytic performance. The pH of the buffer solution, the scanning rate, and the amount of modified material were also optimized for the rapid detection of rutin. A 2-electron-2-proton mechanism, involving a few rapid and consecutive stages, was speculated to occur during rutin oxidation, based on the observed slope of -53 mV/pH. There was an appreciable linear relationship between the reductive peak current from DPV and the rutin concentration, ranging from 0.005-0.05 µmol/L and 0.1-6 µmol/L, with a detection limit of 0.22 nmol/L (S/N = 3). The sensor also demonstrated good selectivity, excellent sensitivity, and reproducibility when analyzing rutin in real plant samples, with satisfactory recovery, and was also highly consistent with results of HPLC, and thus could be used to evaluate the medicinal value of natural vegetation.     

Preparation of COF2 using CO2 and F2 in the electrochemical cell with PbSnF4 as a solid electrolyte

Tetragonal PbSnF₄ was prepared by precipitation method with Pb(NO₃)₂ and SnF₂ aqueous solutions. The product was characterized using X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XFS), and the other chemical analyses. Tetragonal PbSnF₄ exhibited the highest electric conductivity of 3.2 Sm⁻¹ at 473 K in air as a fluoride ion conductor. We have investigated the possibility of COF₂ formation using CO₂ and F₂ in an electrochemical cell with PbSnF₄ as a solid electrolyte. At same time, we tried to produce an electric power from an electrochemical cell. This CO₂/F₂ electrochemical cell was constructed with a tetragonal PbSnF₄ disk having Au electrodes. The electromotive force was about 0.9 V at room temperature for 0.1 MPa CO₂/(0.01 MPa F₂ + 0.09 MPa Ar). However, the short circuit current density was 0.24 A m⁻², which was quite small. This current density was so small that no fluorocarbon compound was detected after 3 h discharge using FT-IR.     

Simultaneous quantification of methylene blue and its major metabolite,azure B,in plasma by LC‐MS/MS and its application for a pharmacokinetic study

A simple and sensitive liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) method was developed for the quantification of methylene blue (MB) and its major metabolite, azure B (AZB), in rat plasma. A simple protein precipitation using acetonitrile was followed by injection of the supernatant on to a Zorbax HILIC Plus column (3.5 µm, 2.1 × 100 mm) with isocratic mobile phase consisting of 5 mM ammonium acetate in 10:90 (v/v) water:methanol at a flow rate of 0.3 mL/min and detection in positive ionization mode. The standard curve was linear over the concentration range from 1 to 1000 ng/mL for MB and AZB with coefficient of determination above 0.9930. The lower limit of quantification was 1 ng/mL using 20 μL of rat plasma sample. The intra‐ and inter‐assay precision and accuracy were <12%. The developed analytical method was successfully applied to the pharmacokinetic study of MB and AZB in rats. Copyright © 2013 John Wiley & Sons, Ltd.     

Preparation of a novel polymer gel electrolyte based on N-methyl-quinoline iodide and its application in quasi-solid-state dye-sensitized solar cell

Using poly(acrylonitrile-co-styrene) as polymer host, 1,2-propanediol carbonate, dimethyl carbonate and ethylene carbonate as mixture solvent, N-methyl-quinoline iodide and iodine as the source of I⁻/I₃ ⁻, a novel polymer gel electrolyte with ionic conductivity of 5.12 × 10⁻³ S· cm⁻¹ at 25°C was prepared by sol-gel and hydrothermal methods. Based on the polymer gel electrolyte, a quasi-solid-state dye-sensitized solar cell was fabricated. The solar cell possess better long-term stability and light-to-electrical energy conversion efficiency of 4.04% under irradiation of 100 mW· cm⁻². The influences of polymer host, solvent, N-methyl-quinoline iodide and temperature on ionic conductivity of the polymer gel electrolyte and the performance of the dye-sensitized solar cell was discussed.     

Sensitivity improvement of a sandwich-type ELISA immunosensor for the detection of different prostate-specific antigen isoforms in human serum using electrochemical impedance spectroscopy and an ordered and hierarchically organized interfacial supramolecular architecture

A gold millielectrode (GME) functionalized with a mixed (16-MHA + EG₃SH) self-assembled monolayer (SAM) was used to fabricate an indirect enzyme-linked immunosorbent assay (ELISA) immunosensor for the sensitive detection of prostate-specific antigen (PSA), a prostate cancer (PCa) biomarker, in human serum samples. To address and minimize the issue of non-specific protein adsorption, an organic matrix (amine-PEG₃-biotin/avidin) was assembled on the previously functionalized electrode surface to build up an ordered and hierarchically organized interfacial supramolecular architecture: Au/16-MHA/EG₃SH/amine-PEG₃-biotin/avidin. The electrode was then exposed to serum samples at different concentrations of a sandwich-type immunocomplex molecule (^BtnAb-Ag_PSA-^HRPAb), and its interfacial properties were characterized using electrochemical impedance spectroscopy (EIS). Calibration curves for polarization resistance (R_P) and capacitance (1/C) vs. total and free PSA concentrations were obtained and their analytical quality parameters were determined. This approach was compared with results obtained from a commercially available ELISA immunosensor. The results obtained in this work showed that the proposed immunosensor can be successfully applied to analyze serum samples of patients representative of the Mexican population.     

A novel ternary polymer electrolyte for LMP batteries based on thermal cross-linked poly(urethane acrylate) in presence of a lithium salt and an ionic liquid

A new ternary polymer electrolyte based on thermally cross-linked poly(urethane acrylate) (PUA), lithium bis(trifluoromethansulfonyl)imide (LiTFSI) and the ionic liquid N-butyl-N-methylpyrrolidinium TFSI (PYR₁₄TFSI) was developed and tested for application in LMP batteries. The polymer electrolyte was a transparent yellow self-standing material with quite good mechanical properties, i.e., comparable to that of a flexible rubber. The room temperature ionic conductivity of the dry polymer electrolyte was found to be as high as 0.1 mS cm⁻¹ for the compound containing 40 wt% of ionic liquid (PYR₁₄TFSI) and a O/Li ratio of 15/1 (Li⁺ from LiTFSI). The thermal analysis of the new cross-linked electrolyte showed that it was homogeneous, amorphous and stable over a wide temperature range extending from −40 °C to 100 °C. The homogeneity of the polymer electrolyte was also confirmed by SEM analysis.     

Development and validation of an LC‐MS/MS method for the determination of a novel thienoquinolin urea transporter inhibitor PU‐48 in rat plasma and its application to a pharmacokinetic study

A specific, sensitive and stable high‐performance liquid chromatographic–tandem mass spectrometry (LC‐MS/MS) method was developed and validated for the quantitative determination of methyl 3‐amino‐6‐methoxythieno [2,3‐b]quinoline‐2‐carboxylate (PU‐48), a novel diuretic thienoquinolin urea transporter inhibitor in rat plasma. In this method, the chromatographic separation of PU‐48 was achieved with a reversed‐phase C₁₈ column (100 × 2.1 mm, 3 μm) at 35°C. The mobile phase consisted of acetonitrile and water with 0.05% formic acid added with a gradient elution at flow rate of 0.3 mL/min. Samples were detected with the triple‐quadrupole tandem mass spectrometer with multiple reaction monitoring mode via electrospray ionization source in positive mode. The retention time were 6.2 min for PU‐48 and 7.2 min for megestrol acetate (internal standard, IS). The monitored ion transitions were mass‐to‐charge ratio (m/z) 289.1 → 229.2 for PU‐48 and m/z 385.3 → 267.1 for the internal standard. The calibration curve for PU‐48 was linear over the concentration range of 0.1–1000 ng/mL (r² > 0.99), and the lower limit of quantitation was 0.1 ng/mL. The precision, accuracy and stability of the method were validated adequately. The developed and validated method was successfully applied to the pharmacokinetic study of PU‐48 in rats.