Instrumentation vacuum system

To analyze any material by MS, the sample must first be vaporized and ionized in the instruments vacuum system. It is generally possible to measure the mass of initial charged species (molecular or parent ion) and those obtained by fragmentation (fragments). In MS, the behavior is studied of the mass-to-charge ratios of volatilized and ionized molecules. The mass spectrum of the fragmentation ions is unique to each molecule as the ion mass pattern is different for each molecule resulting in characteristic mass spectra. 

J. E. Troyan s series of articles on plant startup has a cause/effect table on instrumentation in Part II. This article also has troubleshooting hints for distillation, vacuum systems, heat transfer, and filtration. Here is the table on instrumentation. 

In quadrupole-based SIMS instruments, mass separation is achieved by passing the secondary ions down a path surrounded by four rods excited with various AC and DC voltages. Different sets of AC and DC conditions are used to direct the flight path of the selected secondary ions into the detector. The primary advantage of this kind of spectrometer is the high speed at which they can switch from peak to peak and their ability to perform analysis of dielectric thin films and bulk insulators. The ability of the quadrupole to switch rapidly between mass peaks enables acquisition of depth profiles with more data points per depth, which improves depth resolution. Additionally, most quadrupole-based SIMS instruments are equipped with enhanced vacuum systems, reducing the detrimental contribution of residual atmospheric species to the mass spectrum. 

Different options are available for LC-MS instruments. The vacuum system of a mass spectrometer typically will accept liquid flows in the range of 10-20 p,L min-1. For higher flow-rates it is necessary to modify the vacuum system (TSP interface), to remove the solvent before entry into the ion source (MB interface) or to split the effluent of the column (DLI interface). In the latter case only a small fraction (10-20 iLrnin ) of the total effluent is introduced into the ion source, where the mobile phase provides for chemical ionisation of the sample. The currently available commercial LC-MS systems (Table 7.48) differ widely in characteristics mass spectrometer (QMS, QQQ, QITMS, ToF-MS, B, B-QITMS, QToF-MS), mass range m/z 25000), resolution (up to 5000), mass accuracy (at best <5ppm), scan speed (up to 13000Das-1), interface (usually ESP/ISP and APCI, nanospray, PB, CF-FAB). There is no single LC-MS interface and ionisation mode that is readily suitable for all compounds... 

The Mass Spectrometer Module houses the vacuum system, capillary interface assembly, and ion-trap mass spectrometer in approximately half of the module. Also included are the reagent gas and calibration gas subassembly (a temperature-controlled housing that ensures consistent gas pressures). The other half contains the electronic printed circuit boards, power supplies, and instrument control computer. 

The importance of these surface-analysis techniques has resulted in the development of a range of highly automated instruments. In the effort to obtain multiple analytical data, a trend has occurred during the last ten years to build combined instruments, that is apparatus which will permit measurements by several techniques, in a single vacuum system. In this way, greater utilization of the complex instrumentation involved and a more economic use of the functional parameters of the instruments are ensured. 

In this chapter there is a selection of examples of chemical operations done with the help of a high vacuum system. It must be clear to the reader that many chemical operations have already been described in the earlier parts of this book, for example the various purification procedures assembled in Chapter 4. With regard to measurements, several descriptions of how to proceed will be found in Chapter 3, linked to the description of the various instruments. 

The sample to be analyzed is introduced to the ESI source by means of a flow stream from an HPLC instrument. The sample flows through a stainless-steel needle and then, sprays out in the form of a mist whose droplets hold peptide ions and mobile phase of HPLC. Peptide ions are separated from the mobile phase and subsequently, transferred into a mass analyzer either by a heated capillary or a curtain of nitrogen gas. Desolvation process can be carried out by a vacuum system. 

In analogy to other modern analytical instruments, a computer-based data processing and evaluation system is inserted in all mass spectrometers constructed today. All processes, from sample introduction using an autosampler, e.g., in an ICP-MS, to optimization of experimental parameters in the ion source, ion extraction, separation of ion beams and their registration, the vacuum system and the whole measurement procedure are supported and controlled by a fast and powerful... 

In order to reduce the instrumental background in mass spectrometers, new materials are required or an improvement to the vacuum system. New ion detectors with very low noise should be developed for the measurement of very low isotope ratios. Multi-stage MS-MS instruments could be applied to improve abundance sensitivity. 

Since the launch of the first commercial quadrupole ICP-MS instrument in 1983, the technology has evolved from large, floor-standing, manually operated systems, with limited functionality and relatively poor detection limit capabilities, to compact, sensitive and highly automated routine analytical instruments. In principle, all ICP-MS systems consist of similar components a sample introduction system, the ICP ion source, an interface system, the mass analyser, the detector and a vacuum system [8,11]. 

Instrumentation. Vacuum distillation of parfait column effluents was performed on an FTS Systems model FD-20-84, high-capacity, corrosion-resistant, freeze-drying apparatus modified as described in the text. 

The two magnetic stages are a 30-cm radius followed by an electrostatic analyzer with a radius of 43.26 cm. The vacuum system is metal and is bakeable to 300°C. The analyzer region of the instrument is pumped with ion pumps and is maintained at a pressure 10"9 torr. A combination titanium sublimation-ion pump is used to obtain operating pressures in the source region in the 10"8 torr range. A Nier thick-lens source (8), used in conjunction with a sample wheel arrangement (9), makes it possible to analyze as many as 10 samples per day. 

Space needs to be provided for the auxiliaries, including the lube oil and seal systems, lube oil cooler, intercoolers, and pulsation dampeners. A control panel or console is usually provided as part of the local console. This panel contains instruments that provide the necessary information for start-up and shutdown, and should also include warning and trouble lights. Access must be provided for motor repair and ultimate replacement needs to be considered. If a steam turbine is used, a surface condenser is probably required with a vacuum system to increase the efficiency. All these additional systems need to be considered in the layout and spacing. In addition, room for pulsation dampeners required between stages has to be included. Aftercoolers may also be required with knockout drums. Reference 8 describes the requirements of compressor layouts and provides many useful piping hints. 

The features from which one has to choose In building a SIMS Instrument are as numerous and varied as the problems which the technique can address. Shown conceptlonally In Figure 1 are the various choices for primary bombarding beam formation and emitted particle detection, all encompassed within a vacuum system. 

It has been the purpose of this paper to provide an overview of the basic differences and similarities of the various types of Instruments which detect Ionized particles emitted from surfaces by energetic particle bombardment. Since the scope of secondary ion mass spectrometry Is so broad, It is not surprising that no one Instrument has been designed to perform optimally for all types of SIMS analyses. Design aspects of the primary beam, extraction optics, mass spectrometer, detection equipment and vacuum system must be considered to construct an Instrument best suited for a particular purpose. 

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