Optimization of the atmospheric pressure chemical ionization liquid chromatography mass spectrometry interface

Use of optimized instrument parameters that result from statistical experimentation revealed that the sensitivity of atmospheric pressure chemical ionization (APCI) liquid chromatography-mass spectrometry (LC/MS) is greater than the sensitivity of an optimized Thermabeam? LC/MS interface by about 3 orders of magnitude, when tested on aromatic compounds. APCI is one of the few LC/MS techniques in which the chromatogram is directly comparable with liquid chromatographs that use ultraviolet detection. The optimum instrument parameters for a Finnigan SSQ-7000 APCI LC/MS interface were found at low flow rates (e. g., 0. 1 mL/min), relatively low capillary heat (e. g., 225 °C), and high sheath-gas pressure (e. g., 60 lb/in²). The optimization was achieved by monitoring the responses of sensitivity, fragmentation, and cluster ion formation. The fine tuning for high sensitivity calls for a high percentage of water in the mobile phase. In contrast, a high percentage of organic content in the mobile phase is required to obtain abundant protonated molecular ions with respect to fragmentation and clustering. This is an important consideration for analyses of unknowns.     

Modeling the effects of type and concentration of organic modifiers, column type and chemical structure of analytes on the retention in reversed phase liquid chromatography using a single model

A previously proposed model for representing the retention factor (k) of an analyte in mixed solvent mobile phases was extended to calculate the k of different analytes with respect to the nature of analyte, organic modifier, its concentration and type of the stationary phase. The accuracy of the proposed method was evaluated by calculating mean percentage deviation (MPD) as accuracy criterion. The predicted vs. observed plots were also provided as goodness of fit criteria. The developed model prediction capability compared with a number of previous models (i.e. LSER, general LSER and Oscik equation) through MPD and fitting plots. The proposed method provided acceptable predictions with the advantage of modeling the effects of organic modifiers, mobile phase compositions, columns and analytes using a single equation. The accuracy of developed model was checked using the one column and one analyte out cross validation analyses and the results showed that the developed model was able to predict the unknown analyte retention and the analytes retentions on unknown column accurately.     

Surface/interface phenomena in nano‐multilayer coating under severing tribological conditions

An extensive study of surface/interface phenomena during wear of an adaptive TiAlCrSiYN/TiAlCrN nano‐multilayer coating deposited using physical vapor deposition was undertaken under increasingly severe tribological conditions associated with dry end milling of H13 hardened tool steel. The results of FEM modeling on the temperature/stress distribution at different cutting speeds outline actual cutting conditions on the both rake and flank frictional surfaces of the coated tool. Studies of the surface/interface phenomena were made by means of SEM/high‐resolution transmission electron microscopy/XPS analyses. Results demonstrate that intensifying tribological conditions facilitates improved wear performance of the adaptive coating layer. In extreme tribological conditions of ultra‐performance machining (cutting speed of 500 m/min), the self‐organization process establishes entirely through the formation of a nano‐scale layer of dynamically re‐generating tribo‐ceramic films. The formation of these surface nano‐films results in exceptionally efficient protection of the underlying coating layers. In response to the extreme external environment, the coating layer remained almost undamaged during a long run, demonstrating the capacity to efficiently replenish necessary tribo‐ceramic films. In this way, interconnection of various surface and undersurface processes is established in the hierarchically structured tribo‐films/coating layer. This integral performance is responsible for exceptional wear resistance under intensifying and extreme tribological conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of chloramphenicol in muscle using a particle beam interface for combining liquid chromatography with negative-ion chemical ionization mass spectrometry.

A simple and rapid liquid chromatographic-mass spectrometric analysis of chloramphenicol in calf muscle is presented. A particle beam interface was used, with negative-ion chemical ionization mass spectrometry using methane as the reagent gas. The method specificity was tested for three related compounds, dehydrochloramphenicol, nitrosochloramphenicol and nitrophenylaminopropanediol. The extraction procedures require 5 g of muscle, and the quantification limit is 2 micrograms/kg for chloramphenicol. Residues were detected in calf muscle 48 h after intravenous administration of chloramphenicol (25 mg/kg body weight).     

Modifying the liquid/liquid interface: pores, particles and deposition

The modification of the liquid/liquid interface with solid phases is discussed in this article. Modified interfaces can be formed with molecular assemblies, but here attention is focussed on solid materials such as mesoscopic particles, or microporous and mesoporous membranes. Charge transfer across the modified liquid/liquid interface is considered in particular. The most obvious consequence of the introduction of such modifying components is their effect on the transport to, and the transfer of material across, the liquid/liquid interface, as measured voltammetrically for example. One particularly interesting reaction is interfacial metal deposition, which can also be studied under electrochemical control: the initial formation of metal nuclei at the interface transforms it from the bare, pristine state to a modified state with very different reactivity. Deposition at interfaces between liquids is compared and contrasted with the cases of metal deposition in bulk solution and conventional heterogeneous deposition on conducting solid surfaces. Comparison is also made with work on the assembly of pre-formed micron and nanometre scale solids at the liquid/liquid interface.     

The computer-aided design of a new hydrodynamic device for studying mechanisms of chemical transfer across the liquid|liquid interface

This article outlines the computer-aided design and development of a new hydrodynamic device for investigating the transfer of chemical species between two immiscible liquids. The technique is based on the confluence reactor design, recently introduced for mechanistic and kinetic analysis in single-phase solvent systems. In this article the formulation, numerical procedures and simulation results are presented for the device development. Finite element simulations are presented to establish the fluid dynamic properties of the solvents within the device. In addition, the concentration distribution and current/voltage characteristics of electroactive species introduced under mass transport limited conditions are presented. The simulations reveal the range of optimal transport rate/cell configurations for efficient detection of species partitioning between the two solvent phases.     

Study of mass transfer enhancement on liquid/liquid interface by flow instabilities using gallium liquid electrode

Abstrac  Using liquid gallium electrodes it was proved that electrodiffusion method is a convenient tool for measuring the mass transfer at liquid/liquid interface. It was shown that mass transfer coefficient at the liquid/liquid interface at high Reynolds numbers is much more important in comparison to that measured at the solid/liquid interface at identical geometrical and hydrodynamic conditions. In experiments with the flow induced by the rotation of the upper disc (working ring electrode is placed on the bottom of the immobile disc), the Sherwood number increases in turbulent regime as Sh ∼ Re^1.8 at the liquid/liquid interface, contrary to the traditional law Sh ∼ Re^0.9 at the solid/liquid interface. In laminar regime the Sherwood number at the liquid/liquid and at the solid/liquid interfaces follows the traditional dependence Sh ∼ Re^0.5. It was shown that sharp increasing of the mass transfer coefficient at the liquid/liquid interface is closely related with the appearance of the surface waves, the phenomenon is identified as a Kelvin-Helmholtz type instability. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 4, pp. 482–490. The text was submitted by the authors in English.     

Cloud point phenomena for POE-type nonionic surfactants in a model room temperature ionic liquid

The cloud point phenomenon has been investigated for the solutions of polyoxyethylene (POE)-type nonionic surfactants (C(12)E(5), C(12)E(6), C(12)E(7), C(10)E(6), and C(14)E(6)) in 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), a typical room temperature ionic liquid (RTIL). The cloud point, T(c), increases with the elongation of the POE chain, while decreases with the increase in the hydrocarbon chain length. This demonstrates that the solvophilicity/solvophobicity of the surfactants in RTIL comes from POE chain/hydrocarbon chain. When compared with an aqueous system, the chain length dependence of T(c) is larger for the RTIL system regarding both POE and hydrocarbon chains; in particular, hydrocarbon chain length affects T(c) much more strongly in the RTIL system than in equivalent aqueous systems. In a similar fashion to the much-studied aqueous systems, the micellar growth is also observed in this RTIL solvent as the temperature approaches T(c). The cloud point curves have been analyzed using a Flory-Huggins-type model based on phase separation in polymer solutions.     

Density distribution in the liquid Hg-sapphire interface

We present the results of a computer simulation study of the liquid density distribution normal to the interface between liquid Hg and the reconstructed (0001) face of sapphire. The simulations are based on an extension of the self-consistent quantum Monte Carlo scheme previously used to study the structure of the liquid metal-vapor interface. The calculated density distribution is in very good agreement with that inferred from the recent experimental data of Tamam et al. (J. Phys. Chem. Lett. 2010, 1, 1041-1045). We conclude that, to account for the difference in structure between the liquid Hg-vapor and liquid-Hg-reconstructed (0001) Al(2)O(3) interfaces, it is not necessary to assume there is charge transfer from the Hg to the Al(2)O(3). Rather, the available experimental data are adequately reproduced when the van der Waals interactions of the Al and O atoms with Hg atoms and the exclusion of electron density from Al(2)O(3) via repulsion of the electrons from the closed shells of the ions in the solid are accounted for.     

Detection of hydrogen peroxide produced at a liquid/liquid interface using scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) was used to monitor in situ hydrogen peroxide (H₂O₂) produced at a polarized water/1,2-dichloroethane (DCE) interface. The water/DCE interface was formed between a DCE droplet containing decamethylferrocene (DMFc) supported on a solid electrode and an acidic aqueous solution. H₂O₂ was generated by reducing oxygen with DMFc at the water/DCE interface, and was detected with a SECM tip positioned in the vicinity of the interface using a substrate generation/tip collection mode. This work shows unambiguously how the H₂O₂ generation depends on the polarization of the liquid/liquid interface, and how proton-coupled electron transfer reactions can be controlled at liquid/liquid interfaces.     

A backscattering light detection assembly for sensitive determination of analyte concentrated at the liquid/liquid interface using the interaction of quercetin with proteins as the model system

We report on the construction of a backscattering light (BSL) detection assembly based on detecting angle-dependent light scattering signals, by changing the sample chamber of a common spectrofluorometer. The BSL detection assembly was used to detect, with high sensitivity, the analyte concentrated at the liquid/liquid interface. We applied this assembly to study the interaction of proteins with quercetin in the presence of cationic surfactant. The species resulting from the interaction of quercetin with proteins, when concentrated at the H2O/CCl4 interface, generate enhanced BSL signals characterized at 376.0 nm which were found to be proportional to human serum albumin (HSA) and bovine serum albumin (BSA) in the range of 1-1250 ng mL(-1) and 2-1250 ng mL(-1), respectively. Limits of determination (3sigma) of 75 and 180 pg mL(-1) are reported for the two proteins.     

Currents and photocurrents in organic materials determined by the interface phenomena

The role of interface between molecular material and electrode on currents and photocurrents is considered. Mechanisms of charge carrier injection, electrode recombination and transport are discussed. Particularly thermal, excitonic, photo and tunneling injection of charge carriers, diffusion in presence of image force, interface barrier between electrode and organic materials and two organic materials, non-uniformity of electrodes and other phenomena on charge carrier injection are considered. The data presented in the review which complete theoretical considerations have been taken from previous as well as current literature. The considered phenomena are very important for the analysis of many practical problems for molecular electronic devices such as rectification of current, organic transistors, electroluminescence, photovoltaic effects and some similar problems.     

Pretransitional phenomena in acrylate-based liquid crystal networks

The static Kerr effect is used to study the pretransitional phenomena in polymer networks even in the presence of inherent optical anisotropy of crosslinked materials. The pretransitional phenomena in a liquid crystal polymer and its networks are sensitive to the structure of the crosslinks and their distribution within the network. The bulky network junctions distributed more or less homogeneously within the network serve as defects which decrease the hypothetical second order phase transition temperature T* and suppress the nematic fluctuations in the polymer network above the clearing point.     

Pretransitional phenomena in acrylate-based liquid crystal networks

The static Kerr effect is used to study the pretransitional phenomena in polymer networks even in the presence of inherent optical anisotropy of crosslinked materials. The pretransitional phenomena in a liquid crystal polymer and its networks are sensitive to the structure of the crosslinks and their distribution within the network. The bulky network junctions distributed more or less homogeneously within the network serve as defects which decrease the hypothetical second order phase transition temperature T* and suppress the nematic fluctuations in the polymer network above the clearing point.