Quadrupole mass selector

In either case, a stream of argon gas carries the sample into the plasma torch, where it is ionized at high temperature and injected into the quadrupole mass selector. 

Fig. 6. Schematic diagram of a two-beam apparatus to study H2 formation on grains. Separate beams of H and D atoms are produced in an RF source, with about 70 to 85% dissociation of the feed H2 and D2 gases. The collimated, differentially pumped thermal-energy beams of H and D atoms are brought to the ultrahigh-vacuum scattering chamber, where they are adsorbed onto a grain sample (olivine, pyrolitic graphite, etc.). The HD and D2 produced on the surface are desorbed using temperature-programmed desorption (TPD) and are detected by the quadrupole mass selector (QMS) (Vidali et al, 1998).

FIGURE 52.1 PTR-MS scheme with (1) an ion source, (2) the drift tube, (3) a quadrupole mass selector, and (4) the secondary electron multipher. TMP, turbo molecular pump. 

Laser Ablation Cluster Source with a Quadrupole Mass Selector at the Technische Universitat Miinchen... 

Fig. 4 Typical tandem MS set-up for messenger spectroscopy based on quadrupole mass selector and analyser tuned to the m/z values of the weakly bound ion-ligand complex (Alf -L) and that of the bare ion (AfT"), respectively. The ligand is usually a small molecule (e.g. H2) or a rare gas atom. Figure adapted from Dopfer [117]...

Figure 3. Illustration of the cross-beam machine. N is the nozzle source for the molecular beam, C is the buffer chamber with a beam chopper (not shown), H is the hexapole electric field quantum state selector, U are the homogeneous electric field plates, Q is an on-axis quadrupole mass filter, O is the fast atom beam source, and Q and C,8o are channeltrons.

Figure 2 Schematic view of the apparatus used in studies of the steric effects in gas-surface scattering. A detail of the crystal mount with die orientation rod at 1 cm in front of the surface is shown in die right hand corner. A detailed drawing of the hexapole state selector is given below the main figure. The voltage is applied to die six small rods indicated by an arrow. Key Q quadrupole mass spectrometer R Rempi detector M, crystal manipulator SI, beam source for state selected molecules H electric hexapole state selector C mechanical beam chopper V pulsed gas source S2, continuous molecular beam source. From Tenner et al. [34].

Analysis was carried out by a combination of gas chromatography and mass spectrometry using a Poropak QS (50-80 mesh) column (length 2,2 m. 3,5 mm o.d.) coupled to a Spectramass Selector quadrupole mass spectrometer. 

An example of a similar spectrometer is the one used by Champion et al.9 Primary ions were produced by electron bombardment, accelerated and mass analysed by a 60°, 13-3 cm magnetic mass spectrometer. The ions were then retarded to the desired energy and energy selected by a 127° electrostatic cylindrical velocity selector. The energy resolution was 5 %. The beam half angle is reported to be 18°. The ions then entered a reaction chamber at a pressure of about 10 4torr. The chamber had an exit slit which could be rotated with the detecting system which consisted of another 127° velocity selector, a quadrupole mass spectrometer and an electron multiplier. 

A pioneering work on the simultaneous measurement of the angular and velocity distributions was carried out by Champion et al. [98—101] following the velocity work of Vance and Bailey [94] described above. Their apparatus, a tandem mass spectrometer system, consists essentially of three sections a primary ion gun, a collision chamber, and a product-ion analyser and detector. A mass-analysed, velocity-selected ion beam is directed into the collision chamber containing target gas at low pressure. The product ions are velocity-analysed with a 127° electrostatic velocity selector and mass-analysed in a quadrupole mass filter. The angular distributions of the product ions are obtained by rotating the analyser-detector system about the centre of the collision chamber. 

FIGURE 1. Schematic view of the Nijmegen orientation machine sizes are in mm. The following abbreviations are used so heated quartz N2O source, (p=110 jxm 2 skimmers, collimator scattering chamber, q)=2.0 mm ef extra field hf harp orientation field plates c 3 circular collimators spaced 7.5 mm apart, cp3=5.0 mm, cpi=(p2=2.0 mm 0 barium oven, T=1000 K I1-I4 lens-system, f=1.5 p Polaroid sheet pmt photomultiplier cd collimator detector chamber, quadrupole mass filter pm particle multiplier. The inset shows details of e scattering chamber collimator. 

FIGURE 7 Tandem mass separator. Sample ions enter mass selector 1, where the parent ions are separated. The selected ions next enter the collision chamber, where they collide with gas molecules to form the daughter ions, which are finally separated in the mass selector 2 and expelled for detection. Either magnetic sector or quadrupole mass analyzers or both types mixed can make up a tandem mass spectrometer. A single ion trap can also function as a tandem mass spectrometer performing the same processes as described above in the same location but in consecutive steps. 

The mass spectrometer is a detection and assay device for chemical entities in gas phase. The reactor, which is supplied with reagents, operates in continuous flow. A tiny hole (= 0.4 mm ) is pricked in the reactor, which enables leakage of the reaction mixture. A second hole of the same size is located opposite the former the leakage becomes a molecular beam that passes through the elements of a quadrupole system (Figure 4.7). The latter serves as mass selector. Finally the ion detector enables us to measure the ions created from the molecules of the components of the reaction by the ionization source. The entities are often numerous and the selection is difficult, however, hence the use of the mass spectrometer after a gas-phase chromatograph that has alrea been performed to separate the components. 

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