Pump, diffusion Quadrupole

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. 

Schematic representation of the experimental setup is shown in Fig 1.1. The electrochemical system is coupled on-line to a Quadrupole Mass Spectrometer (Balzers QMS 311 or QMG 112). Volatile substances diffusing through the PTFE membrane enter into a first chamber where a pressure between 10 1 and 10 2 mbar is maintained by means of a turbomolecular pump. In this chamber most of the gases entering in the MS (mainly solvent molecules) are eliminated, a minor part enters in a second chamber where the analyzer is placed. A second turbo molecular pump evacuates this chamber promptly and the pressure can be controlled by changing the aperture between both chambers. Depending on the type of detector used (see below) pressures in the range 10 4-10 5 mbar, (for Faraday Collector, FC), or 10 7-10 9 mbar (for Secondary Electrton Multiplier, SEM) may be established.

Figure 6. Diagram of our 1-atm ion mobility spectrometer (IMS) apparatus (a) stainless steel source gas dilution volume, (b) septum inlet, (c) needle valve, (d) Nj source gas supply, (e) source and drift gas exhaust, (f) flow meter, (g) pressure transducer, (h) insulated box, (i) drift tube, (j) ion source, (k) Bradbury-Nielson gate, (I) Faraday plate/MS aperture, (m) drift gas inlet, (n) universal joint, (o) electrostatic lens element, (p) quadrupole mass filter, (q) 6"-diffusion pump, (r) first vacuum envelope, (s) channeltron electron multiplier, (t) second vacuum envelope, (u) 3"-dif-fusion pump, (v) Nj drift gas, (w) leak valve, (x) on/off valves, (y) fused silica capillary, (z) 4-liter stainless steel dilution volume, (aa) Nj gas supply.

Fig. 1. Photo and illustration of the HRTEM allowing acquisition of images of catalysts under working conditions (4). The microscope is equipped with an FEG, a quadrupole mass spectrometer (QMS), a Gatan image filter (GIF), and a Tietz F144 CCD for data acquisition. The differential pumping system consists of IGPs, turbo molecular pump units (TMP, MDP), and an oil diffusion pump (ODP). The differential pumping stages are set up by apertures inside the TEM column (denoted by black bars) at the objective lens (OL), the first (Cl) condenser aperture, the second (C2) condenser aperture, and the selected area aperture (SA).

Fig. 18. Diagram of reactive scattering apparatus for the study of non-metal reactions A, scattering chamber B, source chambers C, liquid nitrogen cooled cold shield D, detector E, source bulkheads G, liquid nitrogen trap H, oil diffusion pumps N, free radical source P, nozzle source Q, skimmer E, ion source H, liquid He trap I, ion lenses P, photomultiplier Q, quadrupole rods R, light baffle S, slide valve T, radial electric field pumps (from C. F. Carter et al. 02 by permission of the Chemical...

Figure 8.16. TG-MS with a chemical ionization source as described by Bamngarmer and Nachbaur (74). 1, thermobalance 2. furnace 3,3-way valve 4. reaction gas cylinder 5. rotary-pumps 6, coupling line 7. quadrupole mass spectrometer 8. Cl-ion source 9. metering valve 10, ionization gauge 11, analyzer diffusion pump 12. Cl diffusion pump.

Forevacuum 2) = Pump stages 3) = Ion source 4) = GC column 5) Heating for oil diffusion pump 6) = Pump oil 7) = Ion path 8) = Quadrupole rods (separation of ions in the electrical field 9) Secondary emission, electron multiplier (based on Hewlett Packard)... 

In current work the TA Instruments thermal analyst 220 was interfaced [46] to the Hewlett-Packard 5972 series mass selective detector (Figure 15) equipped with a hyperbolic quadrupole mass filter and vapor diffusion high-vacuum pump used in conjunction with a LaserJet 4 Plus printer. The TG analyzer s effluent tube was modified to terminate in a straight 1/4 in. OD glass tube. A 1/4 to 1/6 in. tube reducing union... 

The main analytical instrumentation in the vehicle is a benchtop GC/MS by Hewlett Packard, HP 5890 GC/5970 MSB (mass selective detector). A basic configuration for analyzing liquid samples includes a heated injection port and a capillary fused-silica column interfaced directly to the MS via a heated transfer line. The MS is a quadrupole design operated under vacuum provided by a diffusion pump and backed by a mechanical rotary pump. System operation and data analysis are performed by a Pentium-level personal computer loaded with proprietary software and a NBS spectral library to aid with identification of unknowns. Depending on the mission, a simpler installation may consist of a GC equipped with an appropriate detector such as the electron capture detector (ECD). 

Fig. 2.17. Side elevation of the vacuum setup of the molecular beam machine. Chi vacuum chamber to generate the molecular beam by adiabatic expansion. The oven shown in Fig. 2.19 is inside. Ch2 vacuum chamber where the molecules interact with the laser pulses and are detected by a quadrupole mass spectrometer (QMS) or a Langmuir-Taylor detector (Fig. 2.22). Chi is pumped by an oil diffusion pump (DP) with a cold trap (CT), Ch2 by a turbomolecular pump (TP). Prevacuum is provided by a Roots (RVP) and a rotary valve vacuum pump (RVVP)...

The Molecular Beam Machine and the Detection System. The second component of the real-time MPI experiments is a molecular supersonic beam machine [116] with a quadrupole mass spectrometer (QMS), allowing the detection of ionized molecules and clusters with high sensitivity. A side elevation is shown in Fig. 2.17. The production of the molecular beam and the interaction of the laser pulse trains with the molecular beam are performed in a differentially pumped vacuum apparatus consisting of two separate chambers, which are briefly described in the following two paragraphs. A more detailed sketch of the two-chamber system is presented in Fig. 2.18. The production sub-chamber (oven chamber) is pumped by a 3000 /s oil diffusion pump (Balzers) with a baffle at the flange to the oven chamber to allow a pressure in the chamber of less then 10 mbar. During the experiments the pressure is typically 5 x 10 to 3 x 10 bar. In the second chamber a maximum pressure of 10 mbar is established by a 2200 /s turbomolecular pump (Balzers). 

Under normal circumstances, there is no need for the operator to be concerned about routine maintenance of the mass analyzer. With modem turbomolecular pumping systems, it is highly unlikely there will be any pump- or sample-related contamination problems associated with the quadrupole, magnetic sector, or TOP mass analyzer. This certainly was not the case with some of the early instruments that used oil-based diffusion pumps, because many researchers found that the quadrupole and prefllters were contaminated by oil vapors from the pumps. Today, it is fairly common for turbomolecular-based mass analyzers to require no maintenance of the quadrupole rods over the lifetime of the instrument, other than an inspection carried out by a service engineer on an annual basis. However, in extreme cases, particularly with older instruments, removal and cleaning of the quadrupole assembly might be required to get acceptable peak resolution and abundance sensitivity performance. 

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