Application of manganese (II) phthalocyanine synthesized in situ in the SiO2/SnO2 mixed oxide matrix for determination of dissolved oxygen by electrochemical techniques

This work describes the in situ immobilization of Mn(II) phthalocyanine (MnPc) in a porous SiO₂/SnO₂ mixed oxide matrix obtained by the sol gel processing method. The chemically modified matrix SiO₂/SnO₂/MnPc, possessing an estimated amount of 8 × 10⁻¹⁰ mol cm⁻² of MnPc on the surface, was used to prepare an electrode to analyze dissolved oxygen in water by an electrochemical technique. The electrode was prepared by mixing the material with ultrapure graphite and evaluated using differential pulse voltammetry. Dissolved O₂ was reduced at −0.31 V with a limit of detection (LOD) equal to 7.0 × 10⁻⁴ mmol L⁻¹. A mechanism involving four electrons in O₂ reduction was determined by the rotating disk electrode technique.     

Electrochemical Detection of Nitrite in Meat and Water Samples Using a Mesoporous Carbon Ceramic SiO2/C Electrode Modified with In Situ Generated Manganese(II) Phthalocyanine

Mesoporous carbon ceramic SiO₂/50 wt % C (S_BET=170 m² g^?1), where C is graphite, were prepared by the sol‐gel method. The materials were characterized using N₂ sorption isotherms, scanning electron microscopy, and conductivity measurements. The matrix was used as support for the in situ immobilization of Mn(II) phthalocyanine (MnPc) on their surface. XPS was used to determine the Mn/Si atomic ratios of the MnPc‐modified materials. Pressed disk electrodes were prepared with the MnPc‐modified matrix, and tested as an electrochemical sensor for nitrite oxidation. The linear response range, sensitivity, detection limit and quantification limit were 0.79–15.74 µmol L^?1, 17.31 µA L µmol^?1, 0.02 µmol L^?1 and 0.79 µmol L^?1, respectively, obtained using cyclic voltammetry. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation was 1.7 % for 10 measurements of a solution of 12.63 µmol L^?1 nitrite. The sensor employed to determine nitrite in sausage meat, river and lake water samples showed to be a promising tool for this purpose.     

Method for determining intracapillary solution temperatures: application to sample zone heating for enhanced fluorescent labeling of proteins

A fundamental premise in CE relies heavily on the assumption that temperature within the capillary is accurately known and controlled. Theoretical calculations for sample zone and BGE temperature during voltage application are presented. We propose that transient elevation of the sample zone temperature allowed for denaturing and renaturing of proteins in the presence of a fluorescent dynamic labeling reagent. Comparison with the extent of labeling possible with standard on-column dynamic labeling in the absence of elevated temperatures showed order-of-magnitude increases in the fluorescence detection sensitivity of proteins with low surface hydrophobicity. As a result, this represents an example where excess heating in the sample zone during electrophoresis can be exploited advantageously.     

A microchip sensor for calcium determination

A newly designed glass-PDMS microchip-based sensor for use in the determination of Ca²⁺ ions has been developed, utilizing reflectance measurements from arsenazo III (1,8-dihydroxynaphthalene-3,6-disulfonic acid-2,7-bis[(azo-2)-phenyl arsenic acid]) immobilized on the surface of polymer beads. The beads, produced from cross-linked poly(p-chloromethylstyrene) (PCMS), were covalently modified with polyethylenimine (PEI) to which the Arsenazo III could be adsorbed. The maximum amount of Arsenazo III which could be immobilized onto the PEI-attached PCMS beads was found to be 373.71 mg g⁻¹ polymer at pH 1. Once fabricated, the beads were utilized at the detection point of the microfluidic sensor device with a fiber optic assembly for reflectance measurements. Samples were mobilized past the detection point in the sensor where they interact with the immobilized dye. The sensor could be regenerated and re-used by rinsing with HCl solution. The pH, voltage, linear range, and the effect of interfering ions were evaluated for Ca²⁺ determination using this microchip sensor. At the optimum potential, 0.8 kV, and pH 9.0, the linear range of the microchip sensor was 3.57 × 10⁻⁵ – 5.71 × 10⁻⁴ M Ca²⁺, with a limit of detection (LOD) of 2.68 × 10⁻⁵ M. The microchip biosensor was then applied for clinical analysis of calcium ions in serum with good results. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Complete screening and quasiatomic MVV auger line shapes due to double core ionization

MVV spectra of Rh, Pd, and Ag were measured with and without ionization of their L3 levels. Extra (MMMVV) structure corresponds to the M45M45-->M45VV transition following the L3M45M45 transition. We interpret the MMMVV structure for Pd as quasiatomic in nature from its similarity to the corresponding Ag spectral shape and from its agreement with atomic calculations. The Pd quasiatomic MMMVV spectrum arises from a two final-state hole bound state in the Pd d band filled by screening of the core holes. These findings represent the first unambiguous observation of the influence of complete screening on spectral features.     

Preparative-scale isoelectric focusing separation of enantiomers using a multicompartment electrolyzer with isoelectric membranes

The IsoPrime multicompartment electrolyzer, equipped with a series of isoelectric membranes with closely spaced pI values, was used for the first time for the preparative-scale separation of the enantiomers of dansyl phenylalanine with hydroxypropyl beta-cyclodextrin as resolving agent. The final separation conditions could be established easily in three successive experiments by rationally narrowing the pH steps between the neighboring isoelectric membranes. The final separation yielded products with an enantiomeric excess greater than 99.9%, at production rates of about 0.1 mg/h. The greatest experimental difficulty was caused by the relatively high salt content of the hydroxypropyl beta-cyclodextrin used, which resulted in high conductivity and limited the maximum field strength one could use.     

Detecting electronic states at stacking faults in magnetic thin films by tunneling spectroscopy

Co islands grown on Cu(111) with a stacking fault at the interface present a conductance in the empty electronic states larger than the Co islands that follow the stacking sequence of the Cu substrate. Electrons can be more easily injected into these faulted interfaces, providing a way to enhance transmission in future spintronic devices. The electronic states associated with the stacking fault are visualized by tunneling spectroscopy, and its origin is identified by band structure calculations.