Cap Electrode Research Articles

Narrow-band collisional activation technique for ion trap mass spectrometers.

Narrow-bandwidth signals were applied to the end caps of an ion trap mass spectrometer to excite ions during collisional activation. Excitation waveforms were created from a single-frequency component and a random noise component using a multiplier circuit. Tandem and higher order mass spectrometry experiments (MS3) can be performed without optimization of the supplemental frequency applied to the end cap electrodes. The usefulness of this method of ion excitation is demonstrated using singly and multiply protonated peptide ions as well as sodium-cationized carbohydrates.

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.

A segmented ring, cylindrical ion trap source for time-of-flight mass spectrometry

An ion trap source has been designed for use with time-of-flight (TOF) mass analysis. Two thin diaphragms make up a segmented ring electrode; the end cap electrodes are planar wire mesh. The potential field produced by the rf voltage applied between the ring and end cap electrodes resembles that of the cylindrical ion trap. The trapped ion population for ions created by electron impact exhibits linear growth against a first-order loss that has a time constant of about 50 µs; no ion loss occurs when the electron beam is off. The observed value of q z at low-mass cutoff for rf ion storage is -0.84. Pulsed extraction of all ions is accomplished by switching the trap electrodes from rf to voltages required to provide a linear dc extraction field. The TOF flight path includes a wide energy range reflectron. Better than unit mass resolution is achieved through m/z 500 without collisional ion cooling. With an extraction rate of 1 kHz and a recording rate of 4 spectra per second, a linear working curve is obtained between 36 pg and 18 ng of chlorobenzene delivered chromatographically. The system has demonstrated the potential to achieve a very high sample utilization efficiency at high spectral generation rates.

The non-linear ion trap. Part 3. Multipole components in three types of practical ion trap

A general analytical method is introduced to study quantitatively the multiple components of potential fields in three types of practical ion trap with finite electrode size: (a) the truncated Paul ion trap; (b) the truncated ion trap with modified hyperbolic angel; (c) the truncated ion trap with stretched end-cap distance. Surface charge densities on ring and cap electrodes and capacitances of ion traps are calculated. The analysis points out different properties of the three electrode structure, and present a potential distribution which allows the study of ion motion in these practical ion traps.

Nuclear Reaction Probe of Oxygen Vacancy Migration in Electrically Fatigued PZT Thin Film Capacitors

ABSTRACTThe migration of oxygen vacancies and their entrapment near film-electrode interfaces has been proposed as a cause of fatigue (i.e., polarization weakening) in ferroelectric thin film capacitors. To test this idea, lead zirconate titanate (PZT) thin films were epitaxially deposited by laser ablation on LaAlO3 substrates with yttrium barium cuprate (YBCO) base electrodes. Thin film capacitors were formed by deposition of noble metal (Pt) cap electrodes; half of them were then electrically fatigued by repeated polarization reversals (108 cycles). The distributions of oxygen in the two halves were then compared by means of accelerator-based nuclear backscattering (using the narrow elastic resonance at 3.045 MeV in the scattering of 4He from 16O) throughout the bulk of the PZT films and especially right under the Pt electrodes. We were unable to detect any difference in the oxygen profiles to within the accuracy of measurement, which was about 1 % of the oxygen concentration. Compositional changes, at least involving oxygen, do not seem to be responsible for the striking electrical alterations seen in fatigued PZT.

Boundary effects and collisional activation in a quadrupole ion trap

AbstractThe effects of storing ions at different values of the stability parameters az and qzwere studied in a quadrupole ion trap, using helium or argon as buffer. A region was localized near the boundaries of the stability diagram in which the ions experience an increase in their kinetic energy. This is reflected in the occurrence both of fragmentation due to collisional activation and of a certain extent of ion loss due to unstable trajectories. The results of this excitation, referred to as ‘boundary effects,’ depend on the specific qzat which the ion storage is performed and on the buffer gas used, and point to a simpler means of obtaining tandem mass spectra with the ion trap without the need to apply resonant tickle voltages between the end ‐cap electrodes.

Low-Energy Lone Electron Exhibits Relativistic Hysteresis

There was to have been a birthday party last September in Gerald Gabrielse's lab at the University of Washington. But, sadly, the young honoree met an untimely end just two months shy of its first birthday. Having inadvertently been allowed a bit too much axial excitation, it collided with the cap electrode of the Penning trap that had been its home for more than ten months, and vanished.

Modified extractor gauge

The design and performance of a modified extractor gauge for ultrahigh vacuum pressure measurement is described. The open end construction of the grid cage prevents the x rays from striking the ion collector directly except for those minor indirect x rays that are reflected at respective electrodes. The sensitivity factor is about 8.3×10−2 Pa−1 (11 Torr−1) at an electron current of 1 mA corresponding to the residual gases. Pressure measurements were carried out in the range of 1×10−6 to 9×10−10 Pa (1×10−8 to 7×10−12 Torr). It is confirmed that the x‐ray limit of the gauge is lower than that of the nude‐type B–A gauge. Description is also given of the modified design of the gauge for high vacuum pressure measurements facilitated by the cap electrode mounted on the top of the grid cage.

Some data on the AC breakdown strength of liquid helium in the millimetre gap range

In this paper the first results of an investigation aimed to obtain additional data on breakdown strength of liquid helium are presented; the work is performed under as controlled as possible conditions not too far removed from those relevant to practical engineering applications, by means of a purpose-built helium cryostat whose main features are briefly described. To get results suitable for direct engineering use, a first group of tests was performed with IEC normalized spherical cap electrodes, investigating the statistical behaviour of breakdown strength as a function of gap setting and test conditions. A second group of tests was performed with cylindrical electrodes to get data on the amount of the area effect on the statistical features of breakdown, also as function of test conditions. Finally, a statistical analysis of the obtained data is performed and results are discussed.

Confinement of ions created externally in a radio-frequency ion trap

The various aspects of injecting ions into a three-dimensional radio-frequency quadrupole trap and their trapping for considerable periods of time are investigated by a numerical method. It is shown that for suitably chosen experimental parameters sufficiently long trapping times can be achieved to make this method attractive for on-line high-resolution spectroscopy of short-lived isotopes and of highly charged stable ions. The narrow range of the phase of the driving voltage during which trapping of injected ions occurs is determined. Injection through an end cap electrode is more favorable than ring electrode injection. It is also shown that in the absence of collisions injection through the gaps between the electrodes of the quadrupole ion trap is not feasible. The process of moderating high-energy ions by a thin foil before trapping and the various mechanisms of energy reduction after trapping are discussed.

Emission Spectrographic Determination of Arsenic, Antimony, Cadmium, Lead, Copper, and Zinc in Airborne Particulates Collected on Glass Fiber Filter

Abstract A fast, simple, precise, and direct emission spectrographic method has been developed for the determination of arsenic, antimony, cadmium, lead, copper, and zinc in airborne particulates collected on glass fiber filter. Sample discs, punched out from the glass fiber filter, are packed in a boiler cap electrode. Fifty microliters of an internal standard solution containing 10 mcg/ml of indium are added drop wise on the discs. After evaporating the solution, the electrode is subjected to DC arc excitation (current: 15 A, analytical gap: 2 mm, exposure time: 30 sec with no preburn). The precision of the method is consistently better than ±12%.

Cation Exchange Separation and Spectrographic Determination of Soluble Silicon in Plutonium.

A cation exchange separation of Si from Pu is niade prior to spectrographic determination to reduce the health hazard and spectral interference from Pu. Boiler cap electrodes in conjunction with a sodium carbonate buffer double the sensitivity normally obtained without caps in the same direct current arc methods. The lower limit of detection is 1 ppm Si. The over-all relative standard deviation of the method was within plus or minus 9%. (auth)