Simple cylindrical ion mirror with three elements

A new cylindrical ion mirror has been designed to create an electric field that is non-linear or curved along the flight path axis for general-purpose time-of-flight mass spectrometers. The inclusion of one or two grids is found to improve the radial field homogeneity especially around the aperture. Only three cylindrical electrodes are used in the design. Changing the electrode dimensions and voltages affects the electric field distribution. Once the electrode dimensions are fixed, there are only two adjustable parameters for achieving optimum nonlinear electric field shape. Resolving powers of 7,000 and 16,100 have been achieved with kinetic energy variations of 34 and 10.5%, respectively. Simulations show that the electric field homogeneity in the radial direction enables the use of ion beam diameters up to 15 mm with only modest loss of resolving power. Increasing the mirror diameter could further increase the practical ion beam diameter. This article details the electric field distribution within the cylindrical mirror in both axial and radial directions. The voltages of the middle and rear electrodes affect the resolving power and the kinetic energy range over which focus can be achieved. The predicted arrival time spread for a single m/z value is narrower than that caused by the turn-around time of ions in a gas-phase ion source. In this case, the broad energy range over which good focus is achieved enables the use of higher extraction fields for turn-around time reduction.     

分光光度法测定水样中的硫离子

A new simple spectrophotometric method was proposed for the determination sulphur ion in water samples.In the medium of 0.05 mol/L HCl,sulphur anion turns mixed acid of the silicon and molybdenum into molybdenum blue.Its absorption maxima was found at the wavelength of 700 nm,with a molar absorptivity of 2.48×104L·mol-1·cm-1.Influencing factors such as the amount of reagent and reaction time were optimized,and the interferences from common aions were also investigated.This method was successfully used for t...     

Influence of column geometry on the ion chromatographic separation of aluminium species

The dependence of the degree of disintegration and therefore the applicability of ion chromatography for the speciation of aluminium fluoride species was examined for two different column geometries, a standard bore and a microbore column. Besides mathematical calculations, the temperature of the separation column was varied between –5 and 50??C for the observation of a temperature-dependent decomposition of the species. All species were detected by UV photometry after post-column reaction with Tiron. The results showed that the disintegration of the higher coordinated Al fluoride species (AlF_n with n >2) could be dramatically reduced utilizing the microbore technique. In contrast to the standard bore technique the column temperature is of minor importance. The agreement between speciation data experimentally determined by microbore chromatography and those calculated using stability constants is quite good. The standard bore technique showed bigger differences between calculated and experimentally determined species distributions.     

Influence of column geometry on the ion chromatographic separation of aluminium species

The dependence of the degree of disintegration and therefore the applicability of ion chromatography for the speciation of aluminium fluoride species was examined for two different column geometries, a standard bore and a microbore column. Besides mathematical calculations, the temperature of the separation column was varied between -5 and 50 degrees C for the observation of a temperature-dependent decomposition of the species. All species were detected by UV photometry after post-column reaction with Tiron. The results showed that the disintegration of the higher coordinated Al fluoride species (AlFn with n >2) could be dramatically reduced utilizing the microbore technique. In contrast to the standard bore technique the column temperature is of minor importance. The agreement between speciation data experimentally determined by microbore chromatography and those calculated using stability constants is quite good. The standard bore technique showed bigger differences between calculated and experimentally determined species distributions.     

Laser desorption in transmission geometry inside a Fourier-transform ion cyclotron resonance mass spectrometer

We report here the first application of laser desorption (LD) in transmission geometry (backside irradiation of the sample through a transparent support) inside a Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR). A probe-mounted fiber optic assembly was used to simplify the implementation of this LD technique. This setup requires little or no instrument modifications, has minimum maintenance requirements, and is relatively inexpensive to build. The performance of the probe was tested by determining the molecular weight of a commercial polystyrene standard from its matrix-assisted laser desorption/ionization (MALDI) spectrum. The measured average molecular weight is comparable to that obtained for the same sample by MALDI in the conventional top-illumination arrangement (reflection geometry) and by the manufacturer of the sample by gel permeation chromatography. The average velocities measured for ions evaporated by transmission mode LD of several neat samples are about half the velocity of those obtained by using the reflection geometry. Therefore, transmission mode irradiation of the sample holds promise to desorb ions that are easier to trap in an ICR cell. An oscillating capillary nebulizer was adapted for the deposition of analytes to improve sampling reproducibility.     

Qualitative analysis of the geometry of the hydrogen bond in the homoconjugated pyridine ion

A theoretical analysis of the geometry of the isolated homoconjugated ion formed by interaction of the pyridine molecule with the pyridinium cation was performed. With no o-substituents and no external electric field applied, the hydrogen bond is strongly asymmetric and is characterized by a low barrier to proton transfer between the two chemically equivalent structures. According to the calculations, the most probable averaged distance between the nitrogen atoms forming the hydrogen bond in such homoconjugated cations is about 2.7 ± 0.1 Å.     

Quadrupole ion traps and trap arrays: geometry, material, scale, performance

Quadrupole ion traps are reviewed, emphasizing recent developments, especially the investigation of new geometries, guided by multiple particle simulations such as the ITSIM program. These geometries include linear ion traps (LITs) and the simplified rectilinear ion trap (RIT). Various methods of fabrication are described, including the use of rapid prototyping apparatus (RPA), in which 3D objects are generated through point-by-point laser polymerization. Fabrication in silicon using multilayer semi-conductor fabrication techniques has been used to construct arrays of micro-traps. The performance of instruments containing individual traps as well as arrays of traps of various sizes and geometries is reviewed. Two types of array are differentiated. In the first type, trap arrays constitute fully multiplexed mass spectrometers in which multiple samples are examined using multiple sources, analyzers and detectors, to achieve high throughput analysis. In the second, an array of individual traps acts collectively as a composite trap to increase trapping capacity and performance for a single sample. Much progress has been made in building miniaturized mass spectrometers; a specific example is a 10 kg hand-held tandem mass spectrometer based on the RIT mass analyzer. The performance of this instrument in air and water analysis, using membrane sampling, is described.     

Simple ion chromatographic method for the determination of chlormequat residues in pears

Current methods for quantitative determination of chlormequat residues in food crops are characterized by rather low recoveries and the need for derivatization (in case of gas chromatography, GC), or by high capital investment (in case of liquid chromatography–mass spectrometry, LC–MS). We propose a cation-exchange chromatography method for the analysis of chlormequat in pears. The method is based on extraction of the target compound with 40 mM HCl, followed by centrifugation and filtration. The filtrate is directly injected into an ion chromatograph equipped with a commercially available cation-exchange column and a suppressed conductivity detection system. While the limit of detection (LOD) (0.5 mg/kg) may not be small enough to allow dietary analysis, the method meets all validation requirements and is an alternative for the existing GC and LC–MS methods in quality control.     

Numerical simulation of Monte Carlo ion transport at atmospheric pressure within improved air amplifier geometry

A computational fluid dynamics (CFD) software package ANSYS Fluent was employed for simulation of ion transport at atmospheric pressure between a nano-electrospray ionization (nano-ESI) emitter and the mass spectrometer (MS) sampling inlet tube inside an improved air amplifier device incorporating a radiofrequency ion funnel. The flow field, electric field and the ion trajectory calculations were carried out in separate steps. Parallelized user-defined functions were written to accommodate the additional static and transient electric fields and the elastic ion-gas collisions with the Monte Carlo hard-sphere simulation abilities within Fluent’s environment. The ion transmission efficiency from a nano-ESI emitter to the MS sampling inlet was evaluated for different air amplifier and ion funnel operating conditions by tracking 250 sample reserpine ions. Results show that the high velocity gas stream and the external electric field cause a rapid acceleration of the ion beam and its dispersion along the centreline of the air amplifier which leads to reduction of the space-charge effect and the beam divergence. The radiofrequency potential applied to the ion funnel contributed to additional ion focusing.     

Simple photometric determination of free cyanide ion in aqueous solution with 2,6-dichlorophenolindophenol

In this work, a simple photometric method with high accuracy and precision for measuring trace amounts of free cyanide ion in aqueous solution is demonstrated. Under the evaluated conditions, we could determine CN⁻ concentration in the range of 5–70 ppm easily. The work is based upon the photometric titration of CN⁻ with Co(II) in the presence of 2,6-dichlorophenolindophenol (DCPIP) at λ_max = 602 nm in aqueous solution. The optimal conditions, such as pH, ionic strength, and concentration of chromopher were evaluated. The interence effect of many other cations and anions studied and the results are given here. The optimized titration was successfully used to determine the concentration of free cyanide ion in aqueous solutions.     

Ester-armed cyclens having quadruplicated helical geometry: remarkably stable and selective encapsulation of Na+ ion

A new series of ester-armed cyclens nicely accommodated a Na+ ion in their quadruplicated helical binding spheres and effectively discriminated the cation from Li+ and K+ ions. Crystallographic studies revealed that four ester-functionalized sidearms provided effective coordination with the Na+ ion trapped in the 12-membered cyclen ring. Log K values for their Na+ complexes were estimated as 9-11 in CD3CN or C2D5OD, which were comparable to those of common bicyclic cryptands. FAB-MS, liquid-liquid extraction, and NMR binding experiments demonstrated that the cooperative action of the parent cyclen ring and ester-functionalized sidearms offered stable and selective encapsulation of the Na+ ion based on unique quadruplicated helical geometry.     

Chelate ring geometry,and the metal ion selectivity of macrocyclic ligands. Some recent developments

Abstract

The idea (Hancock, 1992) that the dominant architectural feature in controlling metal ion selectivity in both open-chain and macro-cyclic ligands is the size of the chelate ring is pursued further. It is shown that when more than one or two six-membered chelate rings are present in the complex of a nitrogen donor macrocycle, the steric requirements of the six-membered chelate ring of a M-N bond length of 1.6 Å and N-M-N angle of 109.5° become particularly severe, and can only be met by a small tetrahedral metal ion. Thus, the ligand 16-aneN₄ (1,5,9,13-tetraazacyclohexadecane) forms complexes of low stability with all metal ions studied to date, but a conformer of 16-aneN₄ is identified by MM calculation which is predicted to form complexes of high stability with very small tetrahedral metal ions. The question of the M-O bond length and O-M-O angles that will produce minimum strain in chelate rings containing neutral oxygen donor is addressed. The observation (Hay, 1993) that the geometry around an ethereal oxygen coordinated to a metal ion approximates to trigonal planar rather than tetrahedral leads to ideal M-O-C angles of about 126°, which leads to minimum strain energy with much longer M-L lengths in chelate rings containing neutral oxygen donors than neutral nitrogen donors. It is suggested that this fact accounts for the general tendency of crown ethers to form their most stable complexes with potassium out of the alkali metal ions, and also accounts for the very small macrocyclic effect observed in complexes of macrocycles containing mixed nitrogen and oxygen donor groups. The preferred geometry of four-membered chelate rings is discussed, and it is shown that higher coordination numbers of metal ions are associated with four membered chelate rings, and that four membered chelate rings may be used to engineer preference for larger metal ions. Very rigid reinforced chelate rings are discussed, and it is shown that open-chain ligands with reinforced bridges between the donor atoms can display all the thermodynamic and kinetic aspects associated with macrocyclic ligands.     

Comparative study of different thermospray interfaces with carbamate pesticides: Influence of the ion source geometry

Sixteen carbamate pesticides that belong to four chemical classes (oxime-N-methylcarbamates, aryl N-methylcarbamates, N-phenylcarbamates, and methyl esters of substituted carbamic acids) were investigated via three different commercially available thermospray interfaces and ion sources that exhibit wide differences in source geometry. Comparisons were made between the three interfaces with respect to ion formation and sensitivity of detection. Experimental parameters were standardized to obtain comparable experimental conditions. Very similar mass spectra for most carbamates were obtained that illustrate independence from the geometry of the ionization and desolvation chambers of the interfaces. These findings are in sharp contrast to several literature reports. However, thermally labile carbamates gave unsatisfactory results with regard to spectral compatibility between the interfaces. Such differences were due to thermally assisted hydrolysis reactions that occur in the vaporizer probe prior to ionization and reflect differences in the vaporizer designs. The study proves conclusively that comparable spectra can be obtained under thermospray with different interfaces and mass spectrometers.     

Modeling the effect of the cathode geometry in a DC glow discharge ion source for mass spectrometry

A self-consistent, two-dimensional hybrid fluid-particle model is used to study the effect of cathode geometry on the plasma produced in an argon glow discharge for conditions typically of the commercially available glow discharge mass spectrometer system (VG9000 spectrometer and Megacell source). For a given power supply voltage and gas pressure, we show that the spatial distribution of the plasma in the discharge volume is strongly dependent on the cathode geometry. The plasma created in a discharge with a pin cathode tends to form a ring around the cathode, while the plasma in a discharge with a larger diameter, disk cathode is centered on-axis between the cathode face and the anode. The ion current arriving at the entry plane of the mass spectrometer thus depends strongly on the cathode geometry. This suggests that analytical performance can be enhanced by optimization of the cathode (sample) geometry.     

Simple and sensitive determination of citrinin in Monascus by GC-selected ion monitoring mass spectrometry.

A new method for the qualitative and quantitative analysis of citrinin in Monascus by gas-chromatography-selected ion monitoring (SIM) mass spectrometry has been developed. GC separation of citrinin in Monascus extract was achieved without the need for chemical derivatization, and could be detected as a single peak when the SIM mode selected 5 prominent fragmentations (m/z of 220, 205, 177, 105 and 91). The quantitative detection limit for citrinin was approximately 1 ppb. Finally, the GC-separated analyte from Monascus extract, at a retention time of 10.89 min, was examined by the method of pattern recognition by comparison with a citrinin standard. The results show that the 2 compounds had a 94% similarity when the SIM mode was used.     

Simple optical determination of silver ion in aqueous solutions using benzo crown-ether modified gold nanoparticles

We describe a method for the modification of gold nanoparticles (Au-NPs) with benzo-15-crown-5 that led to the development of a colorimetric assay for Ag(I) ion. The brown color of a solution of the modified Au-NPs turns to purple on addition of Ag(I) ion. The ratio of the UV–vis absorption at 600 nm and 525 nm is proportional to the concentration of Ag(I) ions in the range from 20 to 950 nM, and the detection limit is 12.5 nM. Other metal ions do not interfere if present in up to millimolar concentrations. The method enables a rapid determination of Ag(I) in lake and drinking water and is amenable to bare-eye readout.