Commercial Quadrupole Mass Spectrometer Research Articles

Dopant ionization and efficiency of ion and electron ejection from helium nanodroplets.

Photoionization spectroscopy and mass spectrometry of doped helium (He) nanodroplets rely on the ability to efficiently detect ions and/or electrons. Using a commercial quadrupole mass spectrometer and a photoelectron-photoion coincidence spectrometer, we systematically measure yields of ions and electrons created in pure and doped He nanodroplets in a wide size range and in two ionization regimes-direct ionization and secondary ionization after resonant photoexcitation of the droplets. For two different types of dopants (oxygen molecules, O2, and lithium atoms, Li), we infer the optimal droplet size to maximize the yield of ejected ions. When dopants are ionized by charge-transfer to photoionized He nanodroplets, the highest yield of O2 and Li ions is detected for a mean size of ∼5×104 He atoms per nanodroplet. When dopants are Penning ionized via photoexcitation of the He droplets, the highest yield of O2 and Li ions is detected for ∼103 and ∼105 He atoms per droplet, respectively. At optimum droplet sizes, the detection efficiency of dopant ions in proportion to the number of primary photoabsorption events is up to 20% for charge-transfer ionization of O2 and 2% for Li, whereas for Penning ionization it is 1% for O2 and 4% for Li. Our results are instrumental in determining optimal conditions for mass spectrometric studies and photoionization spectroscopy of molecules and complexes isolated in He nanodroplets.

Laboratory-based validation of the baseline sensors of the ITER diagnostic residual gas analyzer

The divertor-specific ITER Diagnostic Residual Gas Analyzer (DRGA) will provide essential information relating to DT fusion plasma performance. This includes pulse-resolving measurements of the fuel isotopic mix reaching the pumping ducts, as well as the concentration of the helium generated as the ash of the fusion reaction. In the present baseline design, the cluster of sensors attached to this diagnostic's differentially pumped analysis chamber assembly includes a radiation compatible version of a commercial quadrupole mass spectrometer, as well as an optical gas analyzer using a plasma-based light excitation source. This paper reports on a laboratory study intended to validate the performance of this sensor cluster, with emphasis on the detection limit of the isotopic measurement. This validation study was carried out in a laboratory set-up that closely prototyped the analysis chamber assembly configuration of the baseline design. This includes an ITER-specific placement of the optical gas measurement downstream from the first turbine of the chamber's turbo-molecular pump to provide sufficient light emission while preserving the gas dynamics conditions that allow for \ extasciitilde 1 s response time from the sensor cluster [1].

Real-time quadrupole mass spectrometry of hydrothermal gases from the unstable Pisciarelli fumaroles (Campi Flegrei): Trends, challenges and processes

Volcanic gas sampling and post-collection chemical determination in a laboratory may preclude any real-time continuous monitoring of volcanic activity. We describe the development, and show the advantages, of a system used for the continuous monitoring of fumarolic gases discharged from the Pisciarelli site (Campi Flegrei, Southern Italy) based on a commercial quadrupole mass spectrometer (QMS-301 Omnistar™). Although numerous technical problems were addressed due to the ephemeral nature of the emission point and the harsh environment, we also report measurements of the chemical composition of the major gas species emitted from the fumarole for two different periods (in 2009 and 2012). The CO2/H2S, H2S/H2, He/CO2 and CH4/CO2 molar ratios were investigated in order to detect magmatic and/or hydrothermal components in the system, while the N2/O2 ratio was adopted to infer other non-volcanic processes, such as air contamination and mixing with polluted surface waters. The presented methodology allows continuous gas sampling and provides the first evidence of short-term gas variations not available by direct sampling, which is often impractical and hazardous. Compared to the current techniques that are used worldwide for the full characterization of gaseous emissions, i.e. chemical analysis of traditional soda-filled under-vacuum bottles and MultiGAS surveys (laboratory-based and in situ, respectively), QMS-based monitoring is complementary and, in prospect, an alternative. With our method, the geochemical monitoring benefits of the real-time analysis for high sampling rates that can be made comparable to the continuous measurements of geophysical networks. This allows a better understanding of hydrothermal features, particularly of chemical fluctuations occurring on the very short-term, which is fundamental for the evaluation of the evolution of unrest episodes at Campi Flegrei, one of the most hazardous volcanic areas in the world.

Simulation of a QMS Including the Effects of Pressure in the Electron-Impact Ion Source

This paper is concerned with the computer modeling of a quadrupole mass spectrometer (QMS) to include the effect of pressure in the ion source. The paper simulates the spectra over the pressure range from 10-6 to 10-4 mbar. An important contribution is the development of a novel procedure to include pressure dependence of the ion source to allow better prediction of instrument performance. Electron-impact total ionization cross sections in the ionic current expression are calculated using the binary-encounter-Bethe theory for argon gas. The predicted results show good agreement with the experimental results obtained from a commercial QMS used for residual gas analysis.

Mass spectrometry for in-situ volcanic gas monitoring

The principle behind volcanic gas monitoring is that changes in the rate and the composition of the gaseous emissions are associated with major subsurface movement of magma. There has been increased attention directed towards measurements of volcanic gaseous emissions in order to gain a better comprehension of the precursor signals of eruptive activity. There is also a new appreciation of the hazards that gaseous emissions from volcanic sites pose to their immediate surrounding as well as their effects on the atmosphere and global climate. In-situ mass-spectrometer measurements of volcanic gaseous emissions were conducted at several fumarolic sites using a commercial quadrupole mass spectrometer (QMS-300, from SRS Inc) and demonstrated the usefulness of this analytical technique for real-time continuous volcanic gas monitoring applications. The gas concentrations obtained by the MS were in agreement with the values obtained using gas chromatography (GC) at the Hawaiian Volcano Observatory. In addition, the C/S ratios measured by the MS, using both traditional bottle sampling and in-situ sampling, were found to be very similar. Other gases, such as helium, which it is not possible to monitor with any other continuous technique currently available to volcanologists, were easily detected by the mass spectrometer. The field measurements also provided instrument-performance parameters for an ideal field-deployable mass spectrometer. This is the first of a series of articles aiming at the development of a network of mass spectrometers connected via the Internet for real-time, continuous volcanic gaseous emissions monitoring.

Rydberg Electron-Capture Mass Spectrometry of 1,2,3,4 Tetrachlorodibenzo-p-Dioxin

A negative-ion creation technique by Rydberg electron capture (REC) is used to ionise 1,2,3,4 tetrachlorodibenzo- p-dioxin (1,2,3,4-TCDD). Negative ions are mass-analysed by a commercial quadrupole mass spectrometer and also by a home-made mass spectrometer using a quadrupole ion trap. From spectra of 1,2,3,4-TCDD a comparison between the REC ionisation technique and two other soft ionisation techniques, electron capture chemical ionisation (ECCI) and the electron monochromator (EM), are discussed.

Semiconductor and thin film applications of a quadrupole mass spectrometer

Commercial quadrupole mass spectrometer (QMS) residual gas analyzers became available in the late 1960s and have been popular in R&D laboratories, but have found limited use in semiconductor manufacturing. To sample at pressures above 10−5 Torr with ppm sensitivity or better (relative to the total process pressure), differential pumping is usually required. The newly available, small, high-pressure QMS sensors can operate as high as 10–20 mTorr without differential pumping, but provide somewhat lower mass resolution and partial pressure sensitivity than a standard QMS. Applications in semiconductor manufacturing include equipment monitoring, process monitoring, and effluent analysis. Equipment monitoring can include qualification after preventative maintenance, rate-of-rise tests, and leak identification and detection. Usually the burning question is, Why won’t the vacuum chamber pump down? Other uses that are not usually considered include the qualification of replaceable parts: sputter cathodes, electrodes, lamps, shields, etc. In process monitoring, the key question is, Is this process running normally? A manufacturing monitor can be useful simply by providing a comparison between a well-behaved high-yield process and a marginal or failing process. Examples are given for physical vapor deposition (sputtering) processes, chemical vapor deposition, and plasma etching. The effluent from chemical vapor deposition and plasma etch processes can be analyzed to measure the efficiency of process gas utilization or to monitor the efficacy of abatement methods used for the removal of global warming gases.

Ultratrace analysis of calcium with high isotopic selectivity by diodelaser resonance ionisation mass spectrometry

A resonance ionisation mass spectrometer for the ultratrace determination of calcium isotopes is presented. It achieves high overall efficiency, ultra-high isotopic abundance sensitivity of more than 1010 and complete suppression of isobars. The system can be used for isotope ratio studies on stable and long-lived trace isotopes with the final goal of radiodating via 41Ca-determination. For the different applications optical one-, two- or three-step resonance excitation and subsequent ionisation is applied using simple and inexpensive diodelasers. Additional mass analysis is accomplished in a commercial quadrupole mass spectrometer. The experimental set-up and first results on synthetical and meteorite samples are described.

Optimization of a commercial quadrupole mass spectrometer for time-of-flight measurements of laser desorption

Quadrupole mass analyzers (QMAs) are receiving increasing attention for applications in time-of-flight (TOF) studies of laser-induced desorption, ablation and surface reactions in order to extend the information attainable from these experiments. With such a complicated detection device, however, it is easily possible to inadvertantly manipulate the real time-of-flight distribution, for example by missing fast or slow particles. In this work a systematic investigation of the influence of the different QMA parameters on the signal and their interplay was undertaken in laser-induced desorption experiments. The particle pulses were generated by resonant vibrational excitation of condensed benzene films with a TEA CO 2 laser. Our investigations give the optimized configuratioin and setting of potentials for the instrument studied, in terms of sensitivity and energy resolution, and an accurate procedure to determine the drift time of ions in the quadrupole. This makes it possible to detect undistorted time-of-flight distributions with a time resolution of about 5 μs for a range of incident kinetic energies of at least 0–3 eV.

Complementary radiofrequency glow discharge source for a commercial quadrupole mass spectrometer system

A radiofrequency (r.f.) powered glow discharge (GD) atomization/ionization source has been designed and coupled to a commercial GD mass spectrometry system, the VG GloQuad. Preliminary characterizations indicate that this source produces ion beam currents comparable in intensity to conventional d.c. powered sources, with the added advantage of maintaining these intensities in the direct sputter atomization of glass matrix samples. Plasma stabilization times are observed to be of the order of 2–3 min, with long-term (30 min) stability of better than 5% demonstrated for analytes in both metal and glass samples. These preliminary findings suggest that the r.f. GD device might complement the use of d.c. sources for bulk solids and depth resolved analyses.

An electrospray‐ionization mass spectrometer with new features

The construction and performance of an electrospray-ionization mass spectrometer with new features are described. The mass spectrometer consists of a newly designed electrospray ion-source that is plugged directly into a modified commercial quadrupole mass spectrometer with the ions entering the mass analyzer through a long metal capillary tube and three stages of differential pumping. The present ion source differs from previous designs in the combination of techniques employed in the transportation and desolvation of solvated biomolecule ions, prior to mass analysis. Transport of ionized entities between atmospheric pressure and vacuum is carried out through a 203 mm long stainless steel capillary tube with a 0.5 mm bore. Desolvation is effected by the use of controlled heat transfer through the long capillary tube and collisional activation in a region of reduced pressure between the capillary tube exit and the skimmer. Desolvation with this system is convenient and effective and does not involve the strong countercurrent flows of gases that have been used by all previous workers. The effects on the spectra of peptides of capillary tube temperature and desolvation collision energy are investigated. Electrospray-ionization mass spectrometric results are described for thirteen proteins with molecular masses ranging from 5000 to 77,000 Da. The performance of the present instrument, with respect to mass accuracy and sensitivity, is comparable with previously reported systems. The effect of protein concentration in solution on the electrospray mass spectrometric response and charge-state distribution is discussed.

A preliminary attempt at the calibration of a small quadrupole mass spectrometer in the ultra-high vacuum portion of its range

This paper presents experimental results concerning the accuracy of a typical small commercial quadrupole mass spectrometer when it is used to measure absolute partial pressures of the gases normally encountered as residuals in metal ultra-high vacuum systems.

A high mass range quadrupole spectrometer for cluster studies

By modifying a commercial quadrupole mass spectrometer it has been possible to achieve a mass range up to 9000 u without significant losses of transmission. This apparatus has been used in a mercury cluster photoionization experiment.

Supercritical fluid chromatography/mass spectrometry using a simple capillary-direct interface

A simple method for interfacing capillary supercritical fluid chromatography with a commercial quadrupole mass spectrometer (SFC/MS) has been developed that yields good chromatographic peak shapes and good sensitivity. No modification of the mass spectrometer is required, and a single instrument can be used for both SFC/MS and GC/MS with conversion between modes requiring less than 20 min. SFC/MS separations and chemical ionization mass spectra of wax components, a triazine pesticide metabolite, abietic acid, and high molecular weight polycyclic aromatic hydrocarbons are reported.

A Remote Operation Quadrupole Mass Spectrometer Using a Custom Radio-Frequency Link Approach

A commercial quadrupole mass spectrometer (residual gas analyzer, RGA) system has been modified to operate at large separations of its electronics console and sensing head. The methods implemented have made practical applications, as well as operation, of such a system possible for the first time. This advance was stimulated by a need for placing sensors at remote (45 or 60 m) chamber locations for space simulation testing of orbital flight spacecraft. Emphasis is placed on instrument functional requirements and describing the hardware changes and adjustment techniques necessary to assure operation at the extended cable lengths.