Experimental ground stateg J-factor of Ba+ in a Penning ion trap

We observed the Zeeman-splitting of the 6S _1/2 – 6P _1/2 resonance transition of Ba⁺-ions (493.4 nm) in a 6T magnetic field. The ions were stored in a Penning quadrupole trap. We polarized the ground state by optical pumping and in a microwave-optical double resonance experiment we measured the ground state Zeeman-splitting. From the resonance frequency and the cyclotron frequency of electrons stored in the same trap we derived theg-factor of the 6S _1/2 state. The result isg _J(6S _1/2)=2.002 490 6(11), in reasonable agreement with recent calculations.     

A Penning trap for studying cluster ions

We propose to use a Penning trap for spectroscopy of stored cluster ions. A similar device has been built for the purpose of mass measurements of short-lived nuclei produced at the on-line isotope separator ISOLDE/CERN. A resolving power of 500,000 in a mass measurement of³⁹K and an accuracy of 2 × 10^?7 for the⁸⁵Rb/³⁹K mass ratio were obtained. An efficiency for in-flight capture as high as 70% was achieved. The method provides very high sensitivity since typically only 10 to 100 ions are stored in the trap. We intend to perform laser spectroscopy on trapped Na clusters as a first application of the trap technique.     

A broad-band FT-ICR Penning trap system for KATRIN

The KArlsruhe TRItium Neutrino experiment KATRIN aims at improving the upper limit of the mass of the electron antineutrino to about 0.2 eV (90% c.l.) by investigating the -decay of tritium gas molecules . The experiment is currently under construction to start first data taking in 2012. One source of systematic uncertainties in the KATRIN experiment is the formation of ion clusters when tritium decays and decay products interact with residual tritium molecules. It is essential to monitor the abundances of these clusters since they have different final state energies than tritium ions. For this purpose, a prototype of a cylindrical Penning trap has been constructed and tested at the Max-Planck-Institute for Nuclear Physics in Heidelberg, which will be installed in the KATRIN beam line. This system employs the technique of Fourier-Transform Ion-Cyclotron-Resonance in order to measure the abundances of the different stored ion species.     

Damping effects in Penning trap mass spectrometry

Collisions of ions with residual gas atoms in a Penning trap can have a strong influence on the trajectories of the ions, depending on the atom species and the gas pressure. We report on investigations of damping effects in time-of-flight ion-cyclotron resonance mass spectrometry with the Penning trap mass spectrometers ISOLTRAP at ISOLDE/CERN (Geneva, Switzerland) and SHIPTRAP at GSI (Darmstadt, Germany). The work focuses on the interconversion of the magnetron and cyclotron motional modes, in particular the modification of the resonance profiles for quadrupolar excitation due to the damping effect of the residual gas. Extensive experiments have been performed with standard and Ramsey excitation schemes. The results are in good agreement with predictions obtained by analytical continuation of the formulae for the undamped case.     

The motion of small numbers of ions in a Penning trap

An analysis is given of the motion of small numbers of ions (up to three) in the Penning trap. It is shown that the motion is best described in the frame rotating at half the cyclotron frequency, in which the effect of the magnetic field can be described in terms of an effective electrostatic potential. The oscillation frequencies in this frame are calculated for 1, 2 and 3 ions and related to the frequencies observed in the laboratory frame. The orientations of 2- and 3-ion crystals are calculated as a function of the trap parameters.     

Laser-induced low-temperature fluorescence spectroscopy

The absorption and fluorescence spectra of molecules are often very sharp under cryogenic sampling conditions. When a tunable laser is used to excite fluorescence, selective determinations of individual constituents of very complex samples are possible, and the highly resolved fluorescence spectra can serve as 'molecular fingerprints'     

Field-modulated selective ion storage in a quadrupole ion trap

A new method of selective ion storage in a quadrupole ion trap is described. Broadband waveforms were applied to the endcaps of an ion trap to eject unwanted ions by resonance excitation, which enhanced the storage of selected target ions. A unique trapping field amplitude modulation technique allowed the use of waveforms with fewer frequency components. The requirements and methods of calculations for frequency-optimized wave-forms are discussed. Advantages of this method include the reduction of target ion loss that results from collision-activated dissociation. In other applications, equivalent performance, relative to methods that use nonmodulated trapping fields combined with waveforms that have a higher frequency density, was shown.     

The elliptical Penning trap: Experimental investigations and simulations

The application of an additional azimuthal quadrupolar electrostatic field to a Penning trap leads to a field configuration referred to as an elliptical Penning trap. The resulting changes of the radial ion motions have been investigated experimentally and by use of simulations. The eigenfrequencies, i.e., the magnetron frequency and the reduced cyclotron frequency , are found to be shifted with respect to those of the standard Penning trap ω₋, ω₊, respectively. As the shift of the magnetron frequency is larger than that of the reduced cyclotron frequency their sum is also a function of the ellipticity and no longer equal to the cyclotron frequency in the absence of an electric trapping field ω_c=qB/m. The frequency shifts were investigated for argon and fullerene ions. The experimental studies were performed by time-of-flight (ToF) analysis of the ion cyclotron resonance and by Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS). The experimental and simulated values are in agreement with theoretical predictions [M. Kretzschmar, this issue] when the influence of higher multipole terms is taken into account.     

微柱分离中的激光诱导荧光检测

 激光诱导荧光检测 (LIFD)以其高的灵敏度和选择性而被广泛应用于微柱分离技术中。以检测池为轴线 ,概述了激光诱导荧光检测系统新进展及其应用。引用了 5 2篇文献     

Two-species ion clusters in a Paul trap

The ordered structures of two-species ions stored in a Paul trap are simulated by minimizing the total effective potential energy of the ion system. It is shown that the homo-charged two-species ion clusters display separating and mixing structures for different mass and charge ratios. The hetero-charged ion clusters consisting of one light negatively (positively) charged ion and three to six heavy positively (negatively) ions are found to exist stably, and the stability conditions obtained through the perturbative analysis indicate that the ion cluster consisting of more heavy ions has a looser limitation on mass and charge ratios of two-species ions.     

Off-resonance excitation in a linear ion trap

Off-resonance excitation coupled with mass-selective axial ejection of ions in a linear ion trap is shown to allow coherent control of a trapped ion population. Oscillations of the detected ion current have been found to correspond to the degree of detuning of the excitation field from the resonance frequency. Under appropriate excitation conditions coherent oscillations at the excitation frequency are seen that evolve into the ions’ secular frequency on termination of the excitation field. Termination of the excitation field at various points during the off-resonance excitation profile leaves the ions with different degrees of radial excitation. The degree of radial excitation can be controlled by the coherent excitation field and is demonstrated to be useful for collision-induced dissociation.     

Improving IRMPD in a quadrupole ion trap

A focused laser is used to make infrared multiphoton photodissociation (IRMPD) more efficient in a quadrupole ion trap mass spectrometer. Efficient (up to 100%) dissociation at the standard operating pressure of 1 × 10⁻³ Torr can be achieved without any supplemental ion activation and with shorter irradiation times. The axial amplitudes of trapped ion clouds are measured using laser tomography. Laser flux on the ion cloud is increased six times by focusing the laser so that the beam waist approximates the ion cloud size. Unmodified peptide ions from 200 Da to 3 kDa are completely dissociated in 2.5–10 ms at a bath gas pressure of 3.3 × 10⁻⁴ Torr and in 3–25 ms at 1.0 × 10⁻³ Torr. Sequential dissociation of product ions is increased by focusing the laser and by operating at an increased bath gas pressure to minimize the size of the ion cloud.     

Simulations of ion trapping in a micrometer-sized cylindrical ion trap

We have performed detailed SIMION simulations of ion behavior in micrometer-sized cylindrical ion traps (r0 = 1 microm). Simulations examined the effects of ion and neutral temperature, the pressure and nature of cooling gas, ion mass, trap voltage and frequency, space-charge, fabrication defects, and other parameters on the ability of micrometer-sized traps to store ions. At this size scale voltage and power limitations constrain trap operation to frequencies about 1 GHz and rf amplitudes of tens of volts. Correspondingly, the pseudopotential well depth of traps is shallow, and thermal energies contribute significantly to ion losses. Trapping efficiency falls off gradually as qz approaches 0.908, possibly complicating mass-selective trapping, ejection, or quantitation. Coulombic repulsion caused by multiple ions in a small-volume results in a trapping limit of a single ion per trap. If multiple ions are produced in a trap, all but one ion are ejected within a few microseconds. The remaining ion tends to have favorable trapping parameters and a lifetime about hundreds of microseconds; however, this lifetime is significantly shorter than it would have been in the absence of space-charge. Typical microfabrication defects affect ion trapping only minimally. We recently reported (IJMS 2004, 236, 91-104) on the construction of a massively parallel array of ion traps with dimensions of r0 = 1 microm. The relationship of the simulations to the expected performance of the microfabricated array is discussed.     

Estimation of effective ion temperatures in a quadrupole ion trap

A modified Finnigan LCQ quadrupole ion trap has been used to determine the equilibrium constant of the complexation reaction of thiophenolate with 2,2,2-trifluoroethanol. The process is particularly useful as a thermometer reaction because it has an exceptionally large temperature dependence. Using literature values for the thermochemistry, an effective ion temperature of 310 ± 20 K is indicated for the ion trap. This value is much lower than some earlier estimates for ion traps, but is consistent with a recent theoretical analysis and some previous interpretations of experimental data. The results suggest that quadrupole ion traps are suitable for studying gas phase reactions under nearly thermal conditions.     

Nonlinear resonance effects during ion storage in a quadrupole ion trap

Contributions of higher-order fields to the quadrupolar storage field produce nonlinear resonances in the quadrupole ion trap. Storing ions with secular frequencies corresponding to these nonlinear resonances allows adsorption of power from the higher-order fields. This results in increased axial and radial amplitudes which can cause ion ejection and collision-induced dissociation (CID). Experiments employing long storage times and/or high ion populations, such as chemical ionization, ion-molecule reaction studies, and resonance excitation CID, can be particularly susceptible to nonlinear resonance effects. The effects of higher-order fields on stored ions are presented and the influence of instrumental parameters such as radiofrequency and direct current voltage (q_z and a_z values), ion population, and storage time are discussed.     

Mutual storage mode ion/ion reactions in a hybrid linear ion trap

Ion/ion proton transfer reactions involving mutual storage of both ion polarities in a linear ion trap (LIT) that comprises part of a hybrid triple quadrupole/linear ion trap mass spectrometer have been effected. Mutual ion storage in the x- and y-dimensions arises from the normal operation of the oscillating quadrupole field of the quadrupole array, while storage in the z-dimension is enabled by applying unbalanced radio-frequency amplitudes to opposing sets of rods of the array. Efficient trapping (>90%) is achieved for thermalized ions over periods of several seconds. Reactions were demonstrated for multiply charged protein/peptide cations formed by electrospray with anions derived from glow discharge ionization of perfluoro(methyldecalin) (PMD) introduced from the side of the LIT rod array. Doubly and singly charged protein ions are readily formed via ion/ion reactions. The parameters that affect ion/ion reactions are discussed, including the degree of RF unbalance on the LIT rods, vacuum pressure, nature of the buffer gas, reaction time, anion abundance, and the low mass cutoff for ion/ion reaction. The present system has a demonstrated upper mass-to-charge ratio limit of at least 33,000. The system also has high flexibility with respect to defining MS(n) experiments involving both collision-induced dissociation (CID) and ion/ion reactions. Experiments are demonstrated involving beam-type CID in the pressurized collision quadrupole (Q2) followed by ion/ion reactions involving the product ions in the LIT. Ion parking experiments are also demonstrated using the mutual storage ion/ion reaction mode in the LIT, with a parking efficiency over 60%.     

Transmission mode ion/ion proton transfer reactions in a linear ion trap

A new method is described for effecting ion/ion proton transfer reactions that involves storage of analyte ions while oppositely charged ions are transmitted through the stored ion population. In this approach, the products are captured and stored in the linear ion trap for subsequent mass analysis. Charge reduction of multiply charged protein ions is used as an example to illustrate the analytical usefulness of this method. In another variation of the transmission mode ion/ion reaction approach, two charge inversion experiments, implemented by passing analyte ions through a population of multiply charged reagent ions in a LIT, are also demonstrated. A pulsed dual ion source approach coupled with a hybrid triple quadrupole/linear ion trap instrument was used to demonstrate these two methods. The results for ion/ion reactions implemented using these so-called "transmission mode" experiments were comparable to those acquired using the more conventional mutual storage mode, both in terms of efficiency and information content of the spectra. An advantage of transmission mode experiments compared with mutual storage mode experiments is that they do not require any specialized measures to be taken to enable the simultaneous storage of oppositely charged ions.     

Laser-induced fluorescence determination of thallium in sediments

A simple dissolution procedure is decribed for sediments to be analyzed for thallium by Laser-Excited Atomic Fluorescence Spectrometry (LEAFS). It simply uses a nitric – hydrofluoric acid mixture at room temperature (a “cold dissolution” procedure as opposed to the hot acid digestion) followed by a dilution with water (as opposed to the tedious steps of separation and preconcentration). Excellent accuracy (91–106% recoveries) and precision (4–10% relative standard deviation) were demonstrated by the use of five sediment reference materials of diverse origins. The detection limit was estimated to be 0.5 ng/g of thallium. Additionally, a hot plate digestion procedure, using an in-house designed semi-enclosed Teflon beaker, was also investigated; its analytical results agreed with certified values and confirmed the adequacy of the cold dissolution technique. The method is being applied to study the sediment – water interactions in lake environments. Received: 30 December 1996 / Revised: 20 March 1997 / Accepted: 30 March 1997