Separation of potential and kinetic electron emission from Si and W induced by multiply charged neon and argon ions

T he total secondary electron emission yields, gamma(T), induced by impact of the fast ions Neq+ (q = 2-8) and Arq+ (q = 3-12) on Si and Neq+ (q = 2-8) on W targets have been measured. It was observed that for a given impact energy, gamma(T) increases with the charge of projectile ion. By plotting gamma(T) as a function of the total potential energy of the respective ion, true kinetic and potential electron yields have been obtained. Potential electron yield was proportional to the total potential energy of the projectile ion. However, decrease in potential electron yield with increasing kinetic energy of Neq+ impact on Si and W was observed. This decrease in potential electron yield with kinetic energy of the ion was more pronounced for the projectile ions having higher charge states. Moreover, kinetic electron yield to energy-loss ratio for various ion-target combinations was calculated and results were in good agreement with semi-empirical model for kinetic electron emission.

An etched porous interface for on-line capillary electrophoresis-based two-dimensional separation system

The construction and evaluation of an on-column etched fused-silica porous junction for on-line coupling of capillary isoelectric focusing (CIEF) with capillary zone electrophoresis (CZE) are described. Where two separation columns were integrated on a single piece of fused-silica capillary through the etched similar to4 to 5-mm length porous junction along the capillary. The junction is easily prepared by etching a short section of the capillary wall with HF after removing the polyimide coating. The etched section becomes a porous glass membrane that allows only small ions related to the background electrolyte to pass through when high voltage is applied across the separation capillary. The primary advantages of this novel porous junction interface over previous designs (in which the interface is usually formed by fracturing the capillary followed by connecting the two capillaries with a section of microdialysis hollow fiber membrane) are no dead volume, simplicity, and ruggedness, which is particularly well suited for an on-line coupling capillary electrophoresis-based multiple dimensional separation system. The performance of the 2D CIEF-CZE system constructed by such an etched porous junction was evaluated by the analyses of protein mixtures.

Integrated lectin affinity microfluidic chip for glycoform separation

Lectin affinity chromatography was miniaturized into a microfluidic format, which results in improvement of performance, as compared to the conventional method. A lectin affinity monolith column was prepared in the microchannel of a microfluidic chip. The porous monolith was fabricated by UV-initiated polymerization of ethylene dimethacrylate (EDMA) and glycidyl methacrylate (GMA) in the presence of porogeneities, followed by immobilization of pisum sativum agglutinin (PSA) on the monolith matrix. Using electroosmosis as the driven force, lectin affinity chromatographies of three kinds of glycoprotein, turkey ovalbumin (TO), chicken ovalbumin (CO), and ovomucoid (OM), were carried out on the microfluidic system. All the glycoproteins were successfully separated into several fractions with different affinities toward the immobilized PSA. The integrated system reduces the time required for the lectin affinity chromatography reaction to similar to3%, thus, the overall analysis time from 4 h to 400 s. Only 300 pg of glycoprotein is required for the whole separation process. Moreover, troublesome operations for lectin affinity chromatography are simplified.

Separation of acidic and basic compounds in capillary electrochromatography with polymethacrylate-based monolithic columns

Methacrylate-based monolithic columns with electroosmotic flow (EOF) or very weak EOF are prepared by in situ copolymerization in the presence of a porogen in fused-silica capillaries pretreated with a bifunctional reagent. Satisfactory separations of acidic and basic compounds on the column with EOF at either low or high pH are achieved, respectively. With sulfonic groups as dissociation functionalities, sufficient EOF mobility still remains as high as 1.74 x 10(-4) cm(2) s(-1) V-1 at low pH. Under this condition, seven acidic compounds are readily separated within 5.7 min. Moreover, at high pH, the peak shape of basic compounds is satisfactory without addition of any masking amines into running mobile phase since the secondary interaction between the basic compounds and the monolithic stationary phase are minimized at high pH. Reversed-phase mechanism for both acidic and basic compounds is observed under investigated separation conditions. In addition, possibilities of acidic and basic compound separations on a monolithic column with extremely low EOF are discussed. (C) 2004 Elsevier B.V. All rights reserved.

Separation and identification of compounds in Rhizoma chuanxiong by comprehensive two-dimensional liquid chromatography coupled to mass spectrometry

A comprehensive two-dimensional liquid chromatographic separation system based on the combination of a CN column and an ODS column is developed for the separation of components in a traditional Chinese medicine (TCM) Rhizoma chuanxiong. Two columns are coupled by a two-position, eight-port valve equipped with two storage loops and controlled by a computer. The effluent is detected by both the diode array detector and atmospheric pressure chemical ionization (APCI) mass spectrometer. More than 52 components in the methanol extract of R. chuanxiong were resolved and 11 of them were preliminary identified according to their UV and mass spectra. (C) 2004 Elsevier B.V. All rights reserved.

Short columns with molecularly imprinted monolithic stationary phases for rapid separation of diastereomers and enantiomers

Three molecularly imprinted monolithic columns with different length but almost identical column volume had been prepared. It was observed that the separation factors of diastereomers and enantiomers were almost unaffected by column length. However, the short column with dimension of 38 mm x 8 mm W. showed much lower resistance to flow rate so that it could be operated at much higher flow rates. By combining stepwise gradient elution with elevated flow rate, the diastereomers of cinchonine and cinchonidine and the enantiomers of Cbz-DL-Trp and Fmoc-DL-Trp were successfully separated within 3 min on the short column with dimension of 38 mm. x 8 mm i.d.. Based on the above results, a cinchonine imprinted monolithic disk with dimension of 10 mm x 16 mm W. was further developed. The SEM image and the pore size distribution profile showed that large flow-through pores are present on the prepared monolith, which allowed mobile phase to flow through the disk with very low resistance. Chromatographic performances on the monolithic disk were almost unchanged compared with the long columns. A rapid separation of cinchonine and cinchonidine was achieved in 2.5 min at the flow rate of 9.0 ml/min. Furthermore, it was observed that there was almost no effect of the flow rate on the dynamic binding capacity at high flow rates. In addition, the effect of the loading concentration of analytes on the dynamic binding capacity, namely adsorption isotherm, was also investigated. A non-linear adsorption isotherm of cinchonine was observed on the molecularly imprinted monolith with cinchonine as template, which might be a main reason to result in the peak tailing of template molecule. (C) 2004 Elsevier B.V. All rights reserved.