Collisional Cross-Sections with T-Wave Ion Mobility Spectrometry without Experimental Calibration

A method for relating traveling-wave ion mobility spectrometry (TWIMS) drift times with collisional cross-sections using computational simulations is presented. This method is developed using SIMION modeling of the TWIMS potential wave and equations that describe the velocity of ions in gases induced by electric fields. The accuracy of this method is assessed by comparing the collisional cross-sections of 70 different reference ions obtained using this method with those obtained from static drift tube ion mobility measurements. The cross-sections obtained here with low wave velocities are very similar to those obtained using static drift (average difference?=?0.3%) for ions formed from both denaturing and buffered aqueous solutions. In contrast, the cross-sections obtained with high wave velocities are significantly greater, especially for ions formed from buffered aqueous solutions. These higher cross-sections at high wave velocities may result from high-order factors not accounted for in the model presented here or from the protein ions unfolding during TWIMS. Results from this study demonstrate that collisional cross-sections can be obtained from single TWIMS drift time measurements, but that low wave velocities and gentle instrument conditions should be used in order to minimize any uncertainties resulting from high-order effects not accounted for in the present model and from any protein unfolding that might occur. Thus, the method presented here eliminates the need to calibrate TWIMS drift times with collisional cross-sections measured using other ion mobility devices.

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Synthesis of hydrated tungsten(VI) oxide sols by peptization

A method has been developed for the synthesis of hydrated tungsten oxide hydrosols, with this method being based on potassium tungstate hydrolysis followed by peptization of the formed precipitate. The influence of the conditions of precipitation, aging, and washing of the precipitate on the particle phase composition and shape and the degree of precipitate peptization has been studied. Hydrosol-particle sizes have been determined by different methods. It has been found that the dispersed phase of the hydrosols consists mainly of platelike particles of hydrated tungsten oxide WO₃ · 2H₂O with a number-average size of 52 nm. The sols are stable to aggregation in a pH range of 3.0–4.5. The zeta potential of the particles ranges from–33 to–38 mV.     

Chromatographic determination of nitrophenols in aqueous media after two-stage preconcentration using an N-vinylpyrrolidone-based polymer

Two-stage procedures for the preconcentration of nitrophenols (4-nitrophenol, 2,4- and 2,5-dinitrophenol, and 2,4,6-trinitrophenol) from aqueous solutions are proposed. At the first stage, the preconcentration and desorption of nitrophenols under dynamic conditions is carried out. At the second stage, depending on the nature of the desorption solution, the eluate is evaporated (acetonitrile) or saturated with ammonium sulfate and extracted with acetone (aqueous NH₃ solution). The concentration factors are 4000 and 910, respectively. Nitrophenols are determined in concentrates by thin layer chromatography and HPLC, the limits of detection are 1.0–1.8 and 0.25–0.45 μg/L, respectively. The duration of analysis is 200 min.     

Determination of gold and palladium in rocks and ores by atomic absorption spectrometry using two-stage probe atomization

The efficiency of two-stage probe atomization for the determination of gold and palladium in geological samples by electrothermal atomic absorption spectrometry is studied. The effects of temperature–time program and the position of the probe in an atomizer on the fractionation of sample components and the magnitude of the analytical signal are studied. It is demonstrated that gold and palladium can be quantitatively determined by atomic absorption spectrometry in rocks and ores, using a two-stage probe atomization with the limits of detection for gold and palladium 0.01 and 0.04 g/t, respectively.     

Detection and quantification of chitosan aggregates by pressure-assisted capillary zone electrophoresis

An approach to the detection and determination of chitosan aggregates in acetic acid solutions is proposed using pressure-assisted capillary zone electrophoresis. Processes of chitosan aggregation are studied depending on the composition of dispersion medium and storage time. The presence of several species of positively charged chitosan aggregates is revealed for the first time. Particle sizes in the range 20–2500 nm are determined by scanning electron microscopy and static and dynamic light scattering. The dependence of the shape of electropherograms on particle size distribution obtained under the same conditions is found. A trend to changing electrophoretic mobility depending on the size of the aggregate is observed, which enables the approximate evaluation of the polydispersity of chitosan solutions. Chitosan is used for the effective dynamic modification of capillaries, which does not require the introduction of a modifier into the background electrolyte.     

Determination of the surface area of loose metal deposits by impedance spectroscopy

The surface area and fractal dimensions of the surface of loose copper and zinc deposits obtained within 30 and 300 s at direct current sixfold exceeding limiting diffusion current on a smooth electrode were in situ determined by impedance spectroscopy. Impedance measurements were performed in 0.5 M Na₂SO₄ solution. A constant phase element taking into account the distribution of double-layer capacitance over the fractal surface of the electrode was used in the equivalent impedance scheme. Specific surface calculated with regard to the weight of the released metal slightly varied within 300 s (from 6.16 to 6.55 and from 7.12 to 5.89 m²/g for copper and zinc deposits, respectively). Fractal dimensions estimated by chronopotentiometry were given for comparison. Fractal dimensions found by two methods for loose copper and zinc deposits agree with each other; their values (2.19–2.75) testify that the surface of the deposits densely fills the space.     

An electrochemical aptasensor for cytochrome C,based on pillar[5]arene modified with Neutral Red

An electrochemical aptasensor is developed for the highly sensitive determination of cytochrome C, using a change in the redox current of Neutral Red covalently bound to terminal carboxyl groups of decasubstituted pillar[5]arene as a signal. The inclusion of the analyte into the complex with an aptamer reduces peaks of redox current of the dye through the dissociation of electron transfer chain in the surface layer. The aptasensor enables the determination of 1 nM to 1.0 mM of cytochrome C in the presence of 1000-fold excesses of albumin, polyethylene glycol, and lysozyme as models of interfering components in biological fluids.     

Mechanism of reaction of selenium elimination in diacetophenonyl selenide under the action of reduced glutathione

Products of reaction between the organoselenium xenobiotic, diacetophenonyl selenide (1,5-diphenyl-3-selenapenta-1,5-dione), and reduced glutathione at different molar ratios and pH values were studied by HPLC and TLC. Reaction intermediates, S-(acetophenylselenyl)glutathione and glutathione selenodisulfide, and reaction products, acetophenone and hydroselenide anion, were detected. The reaction scheme proposed earlier was confirmed.     

Determination of explosive vapor concentrations with remote sampling in the control of objects

A procedure is proposed for the determination of the vapor concentration of 2,4,6-trinitrotoluene (TNT) in air at a level of 10^–16 g/cm³ in the control of objects for the presence of TNT. The procedure includes preconcentration of TNT vapors and gas chromatographic determination with a limit of TNT detection at a level of 0.08 ± 0.02 pg in a sample. The procedure was applied to the control objects in cells of typical automatic luggage locker with sampling through sampling air ducts. A measure of sample losses as the breakthrough of vapors through sampling air ducts and gas dynamic conditions for the reduction of vapor losses as the ratio of diffusion coefficient to the air duct flow rate were proposed. The time constant of the saturation of the sampling system with TNT vapors and the time constant of its cleaning were determined. It was shown that TNT vapors can be detected virtually satisfactorily near TNT-containing objects with sampling through long channels.     

Chromatographic separation of americium from europium using bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl) pyridine

The separation of americium(III) from europium(III) was achieved utilizing a bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl) pyridine (CA-BTP) chromatographic resin. The extraction chromatographic materials were prepared using various concentrations of CA-BTP. This new, hydrolytically stable extractant was impregnated on an inert polymeric support at 40% loading. The uptake of Am(III) and Eu(III) by this material from 0.1 to 4.0 M aqueous HNO₃ solutions was measured. The resulting dry weight distribution ratios, D _w , indicated a strong preference for Am(III) with little affinity for Eu(III). These results are similar to recently reported solvent extraction studies indicating a maximum uptake of Am(III) in the 0.5–1.0 M HNO₃ range. The resin preparation, performance, and characterization of the Am/Eu separation are reported herein.