Extraction of ions from polar solutions by high-strength electric field pulses

Extraction of ions from solutions of salts in ethylene glycol and water-glycerol mixture by high-strength electric field pulses is investigated. The conditions for stable extraction of ions from a polar liquid in the pulsed regime are ensured by using a track membrane with channels of a nanosize diameter as the interface between the liquid solution and vacuum. The possibility of barrier-free field evaporation of ions from polar liquids in electromembrane ion source for mass-spectrometric analysis of solutions is considered.     

Generation of an extraction electric field in an electromembrane ion source

A mechanism of generating an extraction field in an ion source in which a polymer track membrane with nanodimensional channels is used as an environment-vacuum interface is considered. A high electric field necessary for the effective extraction of ions from a liquid on the membrane surface into the gas phase is maintained by charging the vacuum surface of the membrane. Charging is provided by oppositely charged secondary ions resulting from the disintegration of primary cluster ions on the extraction electrode. A decrease in the source current observed when the vacuum surface discharges counts in favor of this mechanism. The extracted ion energy distribution in the neighborhood of the extraction zone is obtained by the retarding potential method. Various aspects of ion beam formation in the membrane ion source are discussed.     

Field extraction of ions from liquid solutions with the use of polymer track membranes

The general principles of the electric field assisted ion evaporation in the membrane ion source are considered. In the ion source, the liquid sample under investigation is placed in narrow channels of a polymer track membrane, which separates the liquid sample at atmospheric pressure from the vacuum chamber. Stability of the liquid at strong electric fields is provided by a choice of the diameters of channels and the liquid–polymer contact angle. The electric charge on the vacuum–polymer interface is of great importance for creation of the strong electric field near the liquid–vacuum interface. Such a conclusion is made from the computations of the electric field in the framework of the model developed. The mechanism of the electric field assisted evaporation of ions is discussed to explain the observed mass spectra for the ions extracted from liquid.     

Track-membrane-based interface for field evaporation of ions from polar solutions in the diffusion-drift regime

The possibility of realization of barrier-free field evaporation regime for ions from polar solutions in the conditions when the flux of ions from the liquid is limited by their diffusion and drift from the bulk to the surface is considered. The strength of the electric field extracting ions is estimated by simulating electric fields in an ion source with a track membrane as the interface with allowance for the sizes of channels in the membrane and their density. It is shown that when time-dependent electric fields are used, the regime of barrier-free field evaporation can be realized with an appropriate choice of geometrical parameters of the membrane.     

Generation of ions in a pulsed ion source with an interface based on a polymer track membrane

The time-of-flight spectra of ions generated during the extraction of negative ions from the KI solution in water–glycerin mixture by high-strength electric field pulses are studied using a source with an interface based on a polymer track membrane. It has been shown that the ions formed in secondary processes of bombardment of the membrane surface make a considerable contribution to the observed spectra. It has been found that the peaks of negative hydrogen ions have the highest intensity in the spectrum, indicating effective emission of these ions during the bombardment of polyethylene terephthalate by secondary ions with an energy of about 6 keV. The main trends in the modification of the membrane interface to reduce the fraction of secondary ions in the ion beam have been outlined.     

Low-Voltage Membrane Interface for Ion Extraction from Polar Solutions

Electric field that extracts ions from polar solutions to gas phase is calculated for membrane interface with electrode located on the vacuum surface of the membrane. Such a structure can be used to significantly decrease the voltage that provides efficient emission of ions from solution filling the membrane channel and, hence, improve the characteristics of membrane interface.     

PC-88A为载体的大块液膜体系迁移Pb(Ⅱ)动力学研究

采用2-乙基己基膦酸-2-乙基己基单酯(PC-88A)-CHCl₃大块液膜体系,研究了搅拌速度、载体浓度、反应体系温度对Pb离子迁移的影响,原子吸收光谱法测定料液相和解析相中Pb离子浓度,获得了不同反应温度下的表观反应速率常数、Pb离子在膜相中的最大值以及出现最大值的时间、Pb离子在萃取与反萃取反应中进入和流出液膜的最大通量、萃取与反萃取表观反应活化能分别为 31.65和23.11 kJ·mol-1。结果表明,实验值与理论值能够很好地吻合,Pb离子的迁移过程可以用两个串联的准一级不可逆过程描述,化学反应为控速步骤。     

Mitigation of signal suppression caused by the use of trifluoroacetic acid in liquid chromatography mobile phases during liquid chromatography/mass spectrometry analysis via post-column addition of ammonium hydroxide

A method has been developed to reduce the mass spectrometric ion signal suppression associated with the use of TFA as an additive in LC mobile phases. Through post-column infusion of diluted NH(4)OH solution to LC eluents, the ammonium ion introduced causes the neutral analyte-TFA ion pair to dissociate which consequently releases the protonated analyte as free ions into the gas phase (through regular electrospray ionization mechanisms). An ion signal improvement from 1.2 to 20 times for a variety of compounds had been achieved through the application of this method. The molar ratios of NH(4)OH:TFA which result in a reduction of signal suppression were determined to be between 0.5:1 and 50:1. In addition, it was shown that this NH(4)OH infusion method could reduce the level of doubly-charged species and the product ions formed via in-source collision. The use of diluted NH(4)OH solution is favorable since it is compatible with mass spectrometry analysis, and it is applicable in both positive and negative-ion generation mode.     

Analytical laser induced liquid beam desorption mass spectrometry of protonated amino acids and their non-covalently bound aggregates

We have used analytical laser induced liquid beam desorption in combination with high resolution mass spectrometry ( m/Δm≥ 1000) for the study of protonated amino acids (ornithine, citrulline, lysine, arginine) and their non-covalently bound complexes in the gas phase desorbed from water solutions. We report studies in which the desorption mechanism has been investigated. The results imply that biomolecule desorption at our conditions is a single step process involving laser heating of the solvent above its supercritical temperature, a rapid expansion, ion recombination and finally isolation and desorption of only a small fraction of preformed ions and charged aggregates. In addition, we report an investigation of the aqueous solution concentration and pH-dependence of the laser induced desorption of protonated species (monomers and dimers). The experimental findings suggest that the desorption process depends critically upon the proton affinity of the molecules, the concentration of other ions, and of the pH value of the solution. Therefore the ion concentrations measured in the gas phase very likely reflect solution properties (equilibrium concentrations). Arginine self-assembles large non-covalent singly protonated multimers (n = 1...8) when sampled by IR laser induced water beam desorption mass spectrometry. The structures of these aggregates may resemble those of the solid state and may be preformed in solution prior to desorption. A desorption of mixtures of amino acids in water solution enabled us to study (mixed) protonated dimers, one of the various applications of the present technique. Reasons for preferred dimerization - leading to simple cases of molecular recognition - as well as less preferred binding is discussed in terms of the number of specific H-bonds that can be established in the clusters.     

ESCA studies on changes in surface composition under ion bombardment

The influence of ion bombardment on the composition of surfaces was investigated by means of ESCA. The bombardment of metal oxides with inert gas ions results, not only in sputtering of the surface, but also in reduction of the oxides. The rate of reduction is particularly high when the oxide/metal interface is within the range of the bombarding ions. Ion induced reduction was found in oxide layers, thinner than the escape depth of the photoelectrons, on Mo, W, Nb, Ta, Ti, Zr, Si, and Bi. The relationship between reduction phenomena, on the one hand, and the ion energy, angle of incidence, mass of the gas used for bombardment, and ion current density, on the other hand, was investigated in the case of the Mo/Mo-oxide system. Ion bombardment of surfaces may also result in the formation of new compounds. Two examples of this are the formation of carbides through the bombardment of contaminated surfaces and the ion induced formation of C-F compounds from a mixture of K₂SiF₆ and carbon.     

The growth and modification of materials via ion–surface processing

A wide variety of gas phase ions with kinetic energies from 1–10⁷ eV increasingly are being used for the growth and modification of state-of-the-art material interfaces. Ions can be used to deposit thin films; expose fresh interfaces by sputtering; grow mixed interface layers from ions, ambient neutrals, and/or surface atoms; modify the phases of interfaces; dope trace elements into interface regions; impart specific chemical functionalities to a surface; toughen materials; and create micron- and nanometer-scale interface structures. Several examples are developed which demonstrate the variety of technologically important interface modification that is possible with gas phase ions. These examples have been selected to demonstrate how the choice of the ion and its kinetic energy controls modification and deposition for several different materials. Examples are drawn from experiments, computer simulations, fundamental research, and active technological applications. Finally, a list of research areas is provided for which ion–surface modification promises considerable scientific and technological advances in the new millennium.     

中子管用潘宁离子源氢负离子产生机理及实验研究

为了克服目前潘宁(PIG)离子源中子管引出正离子所带来的诸多不利因素,使用PIG型氢负离子源作为中子管的离子源,研究了氢负离子产生的机理,以期在中子管中获得应用。给出了PIG离子源结构,根据氢负离子产生的方式和条件,结合CST软件仿真实验,确定在对阴极和引出孔附近区域存在氢负离子,而且是氢负离子密度比较大的区域。实验中,通过负离子源产生系统证实了氢负离子的存在及分布规律,中子监测仪测量自成靶50mm负离子源陶瓷中子管,中子产额较传统正离子中子管高出一个数量级以上。     

Dispersion in the results of measuring the lifetime of negative ions due to their adsorption on ionization-chamber walls

The time of extraction of negative ions from the ionization chamber of a static mass spectrometer has been measured as a value that significantly exceeds the time of their free exit from the chamber. It has been established that anomalously long ion extraction time is due to their adsorption on the ionization-chamber walls; as a result, their arrival at the analyzer tube is delayed. It has been shown that negative ions, which were initially generated as noninfinitely long-lived ones with respect to auto splitting off of an additional electron, are stabilized to everlasting ions due to adsorption, and the subsequent contribution from infinitely long-lived ions to the total ion flux reaching the recording system distorts the results of measuring the ion lifetime. It has been shown that some of the adsorbed ions are annihilated because of neutralization due to the additional electron tunneling to the surface. The probability of tunneling increases with an increase in temperature; thus, the temperature dependence of the ion lifetime is also distorted.     

离子通道的非均匀分布对环链神经元网络电活动的影响

在电位耦合条件下,利用Morris-Lecar神经元模型构造环链神经元网络,研究了离子通道分布不均匀情形下神经元网络群体电活动的演化和转变问题. 在数值研究中通过改变局部区域的离子通道电导值模拟离子通道的非均匀分布,并对其可能的机制进行了分析. 还研究了网络中局部区域的钙离子电导的差异性和钾离子电导的差异性如何逐渐激发周边神经元,以及诱发的行波如何依赖于神经元之间的耦合强度. 研究发现,增大钙离子电导到一定程度或减小钾离子电导到一定程度可以诱发周围神经元产生兴奋并产生稳定的行波;相反,减小钙离子电导或增大钾离子电导则会减缓或阻断行波的传递. 在同时改变钙离子电导和钾离子电导的情况下,行波的诱发和传播完全依赖于钙离子电导的增量和钾离子电导的减量. 关键词： Morris-Lecar神经元 离子通道的非均匀分布 环链网络     

In situ derivatization-liquid liquid extraction as a sample preparation strategy for the determination of urinary biomarker prolyl-4-hydroxyproline by liquid chromatography-tandem mass spectrometry

Polar analytes that possess protic functional groups have often been treated with alkyl chloroformates to decrease their polarity and increase their volatility prior to gas chromatography-mass spectrometry analysis. This derivatization reaction has two distinct advantages. It proceeds smoothly in aqueous media, and the desired reaction products are efficiently separated from interfering ionic components by their extraction into a water-immiscible organic phase. In the present work, the derivatization-liquid liquid sample preparation was examined in detail for analysis of a potential urinary dipeptide biomarker L-prolyl-4-L-hydroxyproline (PHP) by downstream liquid chromatography coupled to electrospray mass spectrometry. PHP was treated with a series of alkyl and fluoroalkyl chloroformates in aqueous media, and the detected reaction products were investigated. Smooth conversion of PHP into the N-isobutyloxycarbonyl isobutyl ester was accomplished by the coupled action of isobutanol, isobutyl chloroformate and the pyridine catalyst. This derivative afforded a highest detector response from all the derivatized forms examined, including the nonderivatized PHP. A simple isocratic elution on a common RP-C18 HPLC column coupled with tandem mass spectrometry, and use of the synthesized heptadeuterated analog (D7-PHP) as an internal standard, enabled validation of the method and determination of PHP in human urine in less than 5?min. The in situ derivatization-liquid liquid extraction has thus been demonstrated to be a useful sample preparation strategy for the analysis of polar metabolites by liquid chromatography-tandem mass spectrometry in the complex urine matrix.     

Droplet ejection from an interface between two immiscible liquids under pulsed ultrasound

The emphasis of this study is on the ejection of single droplets of a certain size under pulsed ultrasound. Droplet ejection from an interface of two immiscible liquids in this mode, which differs from the well-known ultrasonic fountain (where liquid droplets arise spontaneously), has been experimentally implemented and investigated. The spatial and time evolution of the interface deformation and violation of interface integrity, caused by pulsed acoustic radiation pressure, has been recorded with a high-speed video camera. It is shown that, depending on the ultrasound intensity, three characteristic modes of interface response can be distinguished. In the first (low-intensity)mode, the interface undergoes forced oscillations, without violation of its integrity. In the second (intermediate-intensity) mode, which is in the focus of our study, the interface integrity is violated due to the ejection of a single droplet of a certain size; the latter continuously changes its shape when moving in the second liquid. In the third (high-intensity) mode, the predictable ejection of droplets of a predictable size turns into stochastic ejection of multiple droplets with unpredictable sizes. The dependence of the sizes of single droplets on the parameters of focused ultrasound beam have been measured in the second (stable) mode of ultrasound ejection. Based on these measurements, the range of ultrasound parameters providing controlled generation of single droplets of a specified size is estimated. Differences in the dynamics of interface motion and specific features of droplet generation for the liquid/liquid interface in comparison with the liquid/gas interface are indicated. Possible applications of the observed effects are discussed.     

Analysis of the ion background in an acceleration mass spectrometer of the Siberian Division of the Russian Academy of Sciences

The mechanisms of ion background passage in an acceleration mass spectrometer are investigated. It is shown that the background level is controlled by the interaction between ions and residual gas atoms. An effective method is proposed for suppressing the ion background.     

Extraction of thermalized projectile fragments from gas

The NSCL gas cell and quadrupole ion-guide system has been used to study the thermalization of fast nuclear reaction products in a buffer gas. The fraction of radioactive ions that can be extracted from the gas cell is dramatically suppressed by space charge created by the stopping ions. The results of a review of the ion yields from the NSCL and from other gas cells from the literature with different sizes and different incident particle energies shows an overall consistency with a dramatic decline in extraction efficiency at high ionization rates.     

Structure of Ion-Implanted Alloys with Long-Range Order in a Field Ion Microscope

In the present review we describe the series of investigations in which field ion microscopy is used to study the structural and phase changes in alloys with long-range order and in pure metals after ion implantation by different gas ions. It is demonstrated that ion implantation induces defects of different types spread to considerable depths from the irradiated surface that exceed many times the estimated ion mean free path. It is established that disordering and generation of various defects can be observed under irradiation of the ordered alloy surfaces. In PdCuAg alloys being supersaturated solid solutions, the irradiation provokes the intermittent decomposition. The structure of defects induced by ion implantation including disordered regions, dislocations, dislocation configurations, dislocation barriers, vacancy clusters, and segregations of one of the components is analyzed. The structure and sizes of these defects inside single cascades of displacements are determined.     

Influence of amphotericin B on liquid crystal state of the Cholesterol/Dipalmitoylphosphatidylcholine monolayer in the presence of different metal cations

Amphotericin B is a very effective antifungal drug,but it has an adverse reaction to the membrane of mammals' cells.The interaction between Am B and cholesterol(Chol) causes the formation of pores on the membrane to destroy its integrity.In particular,Am B has a significant effect on the permeability of membrane for K~+ions.It has been reported that Na+ions and Ca~(2+)ions may have some influence on the interaction between amphotericin B and lipid molecules.In this work,the effects of these metal cations on the physical state and intermolecular interaction of the Cholesterol/Dipalmitoylphosphatidylcholine(Chol/DPPC) monolayer with and without Am B have been investigated.The addition of Am B induces the change of physical state of the lipid monolayer from liquid-gel phase to liquid phase.Different metal cations could influence the phase transition of the Am B-lipid monolayer.The K~+ions and Ca2+ions make the obvious phase transition disappear.However,the presence of Na+ions has little influence on the phase transition of the Am B-lipid monolayer.The addition of Am B and the presence of different metal cations weaken the attractive force on the monolayers.After addition of Am B,the force between the molecules is the strongest in the environment of K+ions,thus is the weakest in the environment of Ca~(2+)ions,which may be due to the distribution of these metal cations inside and outside of cells.A large number of K+ions distribute inside of the cells,thus most of Na+and Ca~(2+)ions exist out of the cells.Hence,it may be possible that when Am B molecules are out of the cells,the reaction between the drug and lipid molecules is weaker than that inside the cells.These results may have a great reference value for further studying the toxicity mechanism of Am B and the influence of metal cations on the membrane.