Quadrupol mass spectrometers

Quadrupole mass spectrometers (mass filters) allow ions at each m/z value to pass through sequentially for example, ions at m/z 100, 101, 102 will pass one after the other through the quadrupole assembly so that first m/z 100 is transmitted, then m/z 101, then m/z 102 (or vice versa), and so on. Therefore, the ion collector (or detector) at the end of the quadrupole unit needs to cover only one point or focus in space (Figure 29.1a), and a complete mass spectrum is recorded over a period of time. The ions arrive at the collector sequentially, and ions are detected in a time domain, not in a spatial domain. 

Normal ions are readily and easily observed by quadrupole mass spectrometers. 

Table 2. Scan Functions for a Triple Quadrupole Mass Spectrometer...

It is very evident in Figure 3 that the chemical complexity of Hasteloy presents special problems for mass spectrometric analysis using a quadrupole mass spectrometer with low mass resolution. Molecular ions comprised of combinations of matrix and plasma atoms are formed in abundance and will obscure many elements... 

Molecular ion mass interferences are not as prevalent for the simpler matrices, as is clear from the mass spectrum obtained for the Pechiney 11630 A1 standard sample by electron-gas SNMSd (Figure 4). For metals like high-purity Al, the use of the quadrupole mass spectrometer can be quite satisfiictory. The dopant elements are present in this standard at the level of several tens of ppm and are quite evident in the mass spectrum. While the detection limit on the order of one ppm is comparable to that obtained from optical techniques, the elemental coverage by SNMS is much more comprehensive. 

Demonstration of GDMS feasibility and research into glow-discharge processes has been carried out almost exclusively using the combination of a glow-discharge ion source with a quadrupole mass spectrometer (GDQMS). The combination is inexpensive, readily available and suitable for such purposes. In addition, the quadru-... 

The mass spectrometer usually found on ICPMS instruments is a quadrupole mass spectrometer. This gives high throughput of ions and resolutions of 1 amu. Only a... 

For IBSCA analysis, standard HV or, better, UHV-equipment with turbomolecular pump and a residual gas pressure of less than 10 Pa is necessary. As is apparent from Fig. 4.46, the optical detection system, which consists of transfer optics, a spectrometer, and a lateral-sensitive detector, is often combined with a quadrupole mass spectrometer for analysis of secondary sputtered particles (ions or post-ionized neutrals). 

G. J. Opiteck, J. W. Jorgenson, M. A. Moseley III and R. J. Anderegg, Two-dimensional mia ocolumn HPLC coupled to a single-quadrupole mass spectrometer for the elucidation of sequence tags and peptide mapping , 7. Microcolumn Sep. 10 365-375 (1998). 

These authors also analysed marine diesel fuel with GC X GC, connected to a quadrupole mass spectrometer for identification purposes, although the scan speed of the spectrometer was not quite suited for the fast second-dimension peaks... 

The quadrupole mass spectrometer has been found to be particularly suitable for EGA in thermal analysis. Published reports include descriptions of the various systems used [153—155] and applications in studies of the pyrolysis of polymers [155], minerals [156] and many inorganic solids [157—159]. 

Figure 3.8 Schematic of a triple quadrupole mass spectrometer.

Table 5.21 Intra-assay precision and accuracy of theLC-MS-MS determination of Idoxifene using a triple-quadrupole mass spectrometer. Reprinted from J. Chromatogr., B, 757, Comparison between liquid chromatography-time-of-flight mass spectrometry and selected-reaction monitoring liquid chromatography-mass spectrometry for quantitative determination of Idoxifene in human plasma , Zhang, H. and Henion, J., 151-159, Copyright (2001), with permission from Elsevier Science...

To obtain the maximum concentration of MX2 species, the conditions for these reactions were first optimized by the pyrolytic mass spectrometry method (Kagramanov et al., 1983a). The contents of the mixture during the electron diffraction experiments were controlled by a quadrupole mass spectrometer. 

Secondary ion mass spectrometry (SIMS) is by far the most sensitive surface technique, but also the most difficult to quantify. When a surface is exposed to a beam of ions (Ar", 0.5-5 keV), energy is deposited in the surface region of the sample by a collisional cascade. Some of the energy will return to the surface and stimulate the ejection (desorption) of atoms, ions, and multi-atomic clusters. In SIMS, positive or negative secondary ions are detected directly with a quadrupole mass spectrometer. 

The apparatuses used for the studies of both ammonia synthesis emd hydrodesulfurization were almost identical, consisting of a UHV chamber pumped by both ion and oil diffusion pumps to base pressures of 1 x10 " Torr. Each chamber was equipped with Low Energy Electron Diffraction optics used to determine the orientation of the surfaces and to ascertain that the surfaces were indeed well-ordered. The LEED optics doubled as retarding field analyzers used for Auger Electron Spectroscopy. In addition, each chamber was equipped with a UTI 100C quadrupole mass spectrometer used for analysis of background gases and for Thermal Desorption Spectroscopy studies. 

The usual method of detecting the desorbed molecules in TPR and laser desorption is with a quadrupole mass spectrometer placed a few centimeters from the surface of the crystal. The use of a quadrupole mass spectrometer limits the experiment in several... 

Accessibility to Cu sites was determined by temperature programmed desorption of NO (NO TPD), using an experimental setup similar to that used for TPR, except the detector was a quadrupole mass spectrometer (Balzers QMS421) calibrated on standard mixtures. The samples were first activated in air at 673 K, cooled to room temperature in air, and saturated with NO (NO/He 1/99, vol/vol). They were then flushed with He until no NO could be detected in the effluent, and TPD was started up to 873 K at a heating rate of 10 K/min with an helium flow of 50 cm min. The amount of NO held on the surface was determined from the peak area of the TPD curves. 

The DBMS setup and experimental procedures used in this study were the same as described in more detail elsewhere [Jusys et al., 2001]. Briefly, the DBMS setup consisted of two differentially pumped chambers, a Balzers QMS 112 quadrupole mass spectrometer (MS), a Pine Instruments potentiostat, and a computerized data acquisition system. 

The central transport chamber is an 80-cm-diameter stainless steel vessel, and is pumped by a 1000-1/s turbomolecular pump, which is backed by a small (501/s) turbomolecular pump to increase the compression ratio for hydrogen, and by a 16-m /h rotating-vane pump. UHV is obtained after a bake-out at temperatures above 100°C (measured with thermocouples at the outside surface) of the whole system for about a week. A pressure in the low 10 " -mbar range is then obtained. With a residual gas analyzer (quadrupole mass spectrometer, QMS) the partial pressures of various gases can be measured. During use of the system, the pressure in the central chamber is in the low 10 -mbar range due to loading of samples. Water vapor then is the most abundant species in the chamber. 

The partial pressures of the stable neutral molecules in the discharge (silane, hydrogen, disilane, trisilane) can be measured by a quadrupole mass spectrometer (QMS). The QMS usually is mounted in a differentially pumped chamber, which is connected to the reactor via a small extraction port [286]. In the ASTER system a QMS is mounted on the reactor that is used for intrinsic material deposition. The QMS background pressure (after proper bake-out) is between 10 and 10 mbar. The controllable diameter in the extraction port is adjusted so that during discharge operation the background pressure never exceeds 10"" mbar. 

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