Fourier transform detection in a cylindrical quadrupole ion trap

Broad-band nondestructive ion detection based on induced image current measurement is performed in a quadrupole ion trap having cylindrical geometry. Spectra of krypton and acetophenone are shown to demonstrate the first use of nondestructive detection with a cylindrical ion trap.     

Ion trap mass spectrometry of fluorescently labeled nanoparticles

Mass spectra of fluorescently labeled polystyrene nanoparticles have been obtained using a combined technique of matrix-assisted laser desorption/ionization (MALDI), laser-induced fluorescence (LIF), and a dual quadrupole ion trap mass spectrometer. The spectrometer is designed in such a way that the first trap serves as a trapping and mass-analyzing device, while the second trap serves to capture and concentrate the ions ejected from the first trap for fluorescence detection. An enhancement in the LIF signal by more than 3 orders of magnitude is achieved with the help of the second trap, making mass/charge (m/z) analysis of the nanoparticles possible. Additional unique features of this mass spectrometer include that frequency scan (0.5-50 kHz) at a constant voltage (200 V), instead of voltage scan at a constant frequency, is implemented to widen the spectral analysis range of the instrument. The implementation has allowed the spectrometer to operate at relatively high buffer gas pressures (50 mTorr), crucial for effective trapping of the nanometer-sized particles generated by MALDI. We present in this report the first mass spectra of fluorescently labeled nanoparticles with a size of 27 nm using this new mass spectrometric approach. The utility of this method in the study of biological macromolecules or particles is demonstrated with dye-labeled IgG.     

Broad-band fourier transform quadrupole ion trap mass spectrometry

Broad-band nondestructive ion detection is achieved in a quadrupole ion trap mass spectrometer by impulsive excitation of a collection of trapped ions of different masses and recording of ion image currents induced on a small detector electrode embedded in but isolated from the adjacent end cap electrode. The image currents are directly measured using a simple differential preamplifier, filter, and amplifier combination and then Fourier analyzed to obtain broad-band frequency domain spectra characteristic of the sample ions. The use of the detector electrode provides a significant reduction in capacitive coupling with the ring electrode. This minimizes coupling of the rf drive signal, which can saturate the front-end stage of the detection circuit and prevent measurement of the relatively weaker ion image currents. Although impulsive excitation is preferred due to its broad-band characteristics and simplicity of use, results are also given for narrow-band ac and broad-band SWIFT (stored wave-form inverse Fourier transform) excitation. Data using argon, acetophenone, and n-butylbenzene show that a resolution of better than 1000 is obtained with a detection bandwidth of 400 kHz. An advantage of nondestructive ion detection is the ability to measure a single-ion population multiple times. This is demonstrated using argon as the sample gas with an average remeasurement efficiency of >90%. Tandem mass spectrometry experiments using a population of acetophenone ions are also shown.     

Development of large diameter ECR plasma source

To develop ECR plasma source for industrial applications, we produced a large diameter ECR plasma and examined radial profiles of the ion saturation current as a function of pressure and power. It was found that ECR plasma uniform over 300 mm is produced for pressures higher than 1 mTorr and the electron temperature decreases with increasing pressures.     

Development of large diameter ECR plasma source

To develop ECR plasma source for industrial applications, we produced a large diameter ECR plasma and examined radial profiles of the ion saturation current as a function of pressure and power. It was found that ECR plasma uniform over 300 mm is produced for pressures higher than 1 mTorr and the electron temperature decreases with increasing pressures.     

Electrophoresis of a charged droplet in a dielectric liquid for droplet actuation

Electrophoretic motion of a charged droplet in a dielectric fluid under an electric field has been investigated experimentally for use as a microdroplet actuation method. The effects of the droplet size, electric field strength, and electrolyte concentration and ion species on the charging of an aqueous droplet have been examined. The amount of electrical charging has been measured by two different methods: indirect measurement using the image analysis of droplet motion and direct measurement using the electrometer. Quantitative comparison of the droplet charge measured experimentally and the theoretical value of a perfectly conductive sphere shows that an aqueous droplet is less charged than the corresponding perfectly conductive sphere. The limiting effect on electrical charging is more significant for an electrolyte droplet, and the effect is positively correlated to the electrolyte concentration rather than the ion species. This implies that the low electrical conductivity of water is not a major cause of the limiting effect. The scaling law of the charging amount for a deionized water droplet nearly follows that of the perfect conductor, whereas for an electrolyte droplet, the scaling law exponent is slightly higher. Some advantages and potentials of the current droplet actuation method are also discussed in comparison with the conventional ones.     

A vibrating-wire densimeter for measurements in fluids at high pressures

The paper describes a new type of densimeter especially designed for the accurate measurement of fluid densities at pressures up to 400 MPa. The densimeter makes use of the buoyancy force exerted on a mass immersed in the test fluid to alter the resonant frequency of a thin wire from which the mass is suspended. The resonant frequency of the wire carrying the mass is related to the fluid density by means of working equations which are based on a complete analysis of the fluid motion around the wire. Preliminary results are presented for n-octane at pressures up to about 100 MPa near ambient temperature. The results show that the instrument has a precision of ±0.1 % in density at elevated pressures when evaluated on a relative basis, while the accuracy is estimated to be one of ±0.2%.     

Modeling and analysis of the induced signal detected in electrostatic ion beam trap for mass spectrometry

The induced image charge and image current acquired by a detector tube for mass analysis are simulated using a numerical electrostatic model in the context of the electrostatic ion beam trap (EIBT). With the simulation results, the principle of mass analysis using the induced signal is demonstrated and studied systematically. The results show that the intensity of the detected signal is significantly influenced by the size and configuration of the detector, and also impacted by ion velocity, the number of ions in the ion group, and the ion beam length. The simulation results could not only be used to optimize the size and configuration of the detector and thus to improve the detected signal, but also to support the signal analysis (such as FFT) at an EIBT for mass spectrometry.     

Druckmessung im 10–3 mbar Bereich mit Wärmeleitungs‐ und Membran‐Vakuummeter

Pressure measurement in the mTorr range by thermal conductivity and diaphragm gauges For the reliable and simple pressure measurement in the mTorr range, the thermal conductivity and the capacitance diaphragm gauge can be used. Gauges of both types were employed for measuring the pressure in the bell jar of a piston gauge. The measuring characteristics of the gauges were checked regularly by calibrations and proved to be stable. According to the calibration data, the thermal conductivity gauge apparently is advantageous due to its better zero stability. In the practical use, however, substantial differences between the pressure readings of both gauges were observed. Therefore, in the present work the characteristics of both gauges have been investigated for the case of their actual usage, in which the pressure of an unknown gas has to be measured within a short time period. The investigations reveal, that the thermal conductivity gauge suffers from its slow response at small pressures and its dependency on gas species. In the present application, the capacitance diaphragm gauge proves as the far superior gauge.     

Spectroscopic imaging ellipsometry: real-time measurement of single, intact wood pulp fibers

A nondestructive method based on spectroscopic ellipsometry has been developed and demonstrated for the real-time measurement of a single pulp fiber's microfibril angle and phase retardation, with the latter proportional to the cell wall thickness. The method uses an optical arrangement insensitive to the sample's orientation in combination with a proper spectral analysis of the sample's image. The optical arrangement and the measurement principle of the method are described. To test the new method, equipment functioning as a spectroscopic imaging ellipsometer was constructed according to the arrangement, and measurements were carried out in which single pulp fibers and ordinary wave plates were measured. The test measurements and results are described and presented.     

A method for measuring vapor pressures of low-volatility organic aerosol compounds using a thermal desorption particle beam mass spectrometer

A temperature-programmed thermal desorption method for measuring vapor pressures of low-volatility organic aerosol compounds has been developed. The technique employs a thermal desorption particle beam mass spectrometer we have recently developed for real-time composition analysis of organic aerosols. Particles are size selected using a differential mobility analyzer, sampled into a high-vacuum chamber as an aerodynamically focused beam, collected by impaction on a cryogenically cooled surface, slowly vaporized by resistive heating, and analyzed in a quadrupole mass spectrometer. A simple evaporation model developed from the kinetic theory of gases is used to calculate compound vapor pressures over the temperature range of evaporation. The data are fit to a Clausius-Clapeyron equation to obtain a relationship between vapor pressure and temperature and to determine the heat of vaporization. The technique has been evaluated using C13-C18 monocarboxylic and C6-C8 dicarboxylic acids, which have vapor pressures at 25 degrees C of approximately 10(-4) - 10(-6) Pa, but less volatile compounds can also be analyzed. The method is relatively simple and rapid and yields vapor pressures and heats of vaporization that are in good agreement with literature values. The technique will be used to generate a new database of vapor pressures for low-volatility atmospheric organic compounds.     

Operating characteristics of the hollow anode glow discharge ion source

In this work, a new shape of a glow discharge ion source with axial extraction has been designed and constructed. High output ion beam current can be extracted axially in a direction normal to the discharge region without using extraction system. Optimization of the distance between the anode and the cathode has been determined using argon gas. It is found that the optimum gap distance between the anode and the cathode is equal to 3.5 mm, where stable discharge current and maximum output ion beam current can be obtained. The discharge characteristics of the ion source at different operating gas pressures have been measured at this optimum distance between the anode and the cathode. A disk of Teflon insulator has been put between the anode and the cathode. This disk was covering the cathode area and reducing the discharge area on the cathode surface for discharge confinement, therefore, a higher output ion beam current could be obtained.     

C60 secondary ion mass spectrometry with a hybrid-quadrupole orthogonal time-of-flight mass spectrometer

A hybrid quadrupole orthogonal time-of-flight mass spectrometer optimized for matrix-assisted laser desorption ionization (MALDI) and electrospray ionization has been equipped with a C 60 cluster ion source. This configuration is shown to exhibit a number of characteristics that improve the performance of traditional time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments for the analysis of complex organic materials and, potentially, for chemical imaging. Specifically, the primary ion beam is operated as a continuous rather than a pulsed beam, resulting in up to 4 orders of magnitude greater ion fluence on the target. The secondary ions are extracted at very low voltage into 8 mTorr of N 2 gas introduced for collisional focusing and cooling purposes. This extraction configuration is shown to yield secondary ions that rapidly lose memory of the mechanism of their birth, yielding tandem mass spectra that are identical for SIMS and MALDI. With implementation of ion trapping, the extraction efficiency is shown to be equivalent to that found in traditional TOF-SIMS machines. Examples are given, for a variety of substrates that illustrate mass resolution of 12,000-15,600 with a mass range for inorganic compounds to m/ z 40,000. Preliminary chemical mapping experiments show that with added sensitivity, imaging in the MS/MS mode of operation is straightforward. In general, the combination of MALDI and SIMS is shown to add capabilities to each technique, providing a robust platform for TOF-SIMS experiments that already exists in a large number of laboratories.     

功率MOSFET单粒子烧毁测试技术研究

总结了2种单粒子烧毁测试方法.在非破坏性测试原理基础上,研制成功针对星用功率MOSFET的单粒子烧毁动态测试系统.系统在锎源单粒子效应实验装置调试通过.利用该系统,在HI-13串列加速器上初步完成了星用MOSFET单粒子烧毁验证实验.     

On-line velocity measurements using phase probes at the SuperHILAC

Phase probes have been placed in several external beam lines at the LBL heavy ion linear accelerator (SuperHILAC) to provide nondestructive velocity measurements independent of the ion being accelerated [B. Leemann, D. Brodzik, B. Feinberg and D. Howard, IEEE Trans. Nucl. Sci. NS-32 (1985)1982]. The system uses three probes in each line to obtain accurate velocity measurements at all beam energies. Automatic gain control and signal analysis are performed so that the energy/nucleon along with up to three probe signals are displayed on a vector graphics display with a refresh rate better than twice per second. The system uses a sensitive pseudocorrelation technique to pick out the signal from the noise, features simultaneous measurements of up to four ion velocities when more than one beam is being accelerated, and is controlled by a touch-screen operator interface. It is accurate to within ±0.25% and has provisions for on-line calibration tests. The phase probes thus provide a velocity measurement independent of the mass defect associated with the use of crystal detectors, which can become significant for heavy elements. They are now used as a routine tuning aid to ensure proper bunch structure, and as a beam velocity monitor.     

Surface mass spectrometry of two component drug-polymer systems: novel chromatographic separation method using gentle-secondary ion mass spectrometry (G-SIMS)

In recent years, there has been an increase in the use of time-of-flight secondary ion mass spectrometry (TOF-SIMS) for characterizing material surfaces. A great advantage of SIMS is that the analysis is direct and has excellent spatial resolution approaching a few hundred nanometers. However, the lack of the usual separation methods in mass spectrometry such as chromatography or ion mobility combined with the complexity of the heavily fragmented ions in the spectra means that the interpretation of multicomponent spectra in SIMS is very challenging indeed. The requirements for high-definition imaging, with say 256 × 256 pixels, in around 10 min analysis time places significant constraints on the instrument design so that separation using methods such as ion mobility with flight times of milliseconds are incompatible. Clearly, traditional liquid and gas chromatographies are not at all possible. Previously, we developed a method known as Gentle-SIMS (G-SIMS) that simplifies SIMS spectra so that the dominant ions are simply related to the structure of the substances analyzed. The method uses a measurement of the fragmentation behavior under two different primary ion source conditions and a control parameter known as the g-index. Here, we show that this method may be used "chromatographically" to separate the mass spectra of a drug molecule from the matrix polymer. The method may be used in real-time and is directly compatible with the majority of TOF-SIMS instruments. The applicability to other imaging mass spectrometeries is discussed.     

MALDI-FTICR imaging mass spectrometry of drugs and metabolites in tissue

A new approach is described for imaging mass spectrometry analysis of drugs and metabolites in tissue using matrix-assisted laser desorption ionization-Fourier transform ion cyclotron resonance (MALDI-FTICR). The technique utilizes the high resolving power to produce images from thousands of ions measured during a single mass spectrometry (MS)-mode experiment. Accurate mass measurement provides molecular specificity for the ion images on the basis of elemental composition. Final structural confirmation of the targeted compound is made from accurate mass fragment ions generated in an external quadrupole-collision cell. The ability to image many small molecules in a single measurement with high specificity is a significant improvement over existing MS/MS based technologies. Example images are shown for olanzapine in kidney and liver and imatinib in glioma.     

Observation of increased ion cyclotron resonance signal duration through electric field perturbations

Ion motion in Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is complex and the subject of ongoing theoretical and experimental studies. Two predominant pathways for the loss of ICR signals are thought to include damping of cyclotron motion, in which ions lose kinetic energy and radially damp toward the center of the ICR cell, and dephasing of ion coherence, in which ions of like cyclotron frequency become distributed out of phase at similar cyclotron radii. Both mechanisms result in the loss of induced ion image current in FTICR-MS measurements and are normally inseparable during time-domain signal analysis. For conventional ICR measurements which take advantage of ion ensembles, maximization of the ion population size and density can produce the desired effect of increasing phase coherence of ions during cyclotron motion. However, this approach also presents the risk of coalescence of ion packets of similar frequencies. In general, ICR researchers in the past have lacked the tools necessary to distinguish or independently control dephasing and damping mechanisms for ICR signal loss. Nonetheless, the ability to impart greater phase coherence of ions in ICR measurements will allow significant advances in FTICR-MS research by improving the current understanding of ICR signal loss contributions of dephasing and damping of ion ensembles, increasing overall time-domain signal length, and possibly, resulting in more routine ultrahigh resolution measurements. The results presented here demonstrate the ability to employ a high density electron beam to perturb electric fields within the ICR cell during detection of cyclotron motion, in an approach we call electron-promoted ion coherence (EPIC). As such, EPIC reduces ICR signal degradation through loss of phase coherence, and much longer time-domain signals can be obtained. Our results demonstrate that time-domain signals can be extended by more than a factor of 4 with the implementation of EPIC, as compared to conventional experiments with otherwise identical conditions. The application of EPIC has also been observed to reduce the appearance of peak coalescence. These capabilities are not yet fully optimized nor fully understood in terms of the complex physics that underlies the enhancement. However, the enhanced time-domain signals can result in improved resolution in frequency-domain signals, and as such, this result is important for more efficient utilization of FTICR-MS. High resolution and accurate mass analysis are prime motivating factors in the application of advanced FTICR technology. We believe the approach presented here and derivatives from it may have significant benefit in future applications of advanced FTICR technology.     

Ion and neutral temperatures in an electron cyclotron resonance plasma

Transverse ion and neutral temperatures at the electron cyclotron resonance position were measured in an electron cyclotron resonance (ECR) plasma using a high-resolution optical emission spectroscopy of Doppler profiles of Ar and Ar⁺ transition. The transverse ion temperature increase from approximately 0.4 to 1.0 eV as the operating gas pressure is lowered from 1.0 to 0.1 mTorr. On the other hand, the transverse neutral temperature is much lower than the transverse ion temperature. By means of Langmuir probe measurement, large-amplitude potential fluctuation was observed at the ECR position under the low gas pressure. These observations suggest that the large-amplitude potential fluctuation directly affects the transverse ion temperature.     

Absolute energy measurement of heavy ion beams using a resonant time-of-flight system

A resonant time-of-flight measurement system has been put into operation at the ATLAS facility for the determination of the energy of heavy ion beams. The system provides continuous, nondestructive monitoring of the beam energy. The system provides relative energy determination with a precision of . Absolute energy is determined to an accuracy of 10⁻³. A variety of beam tests have been performed to study the properties of the system.