Types of Point Ion Collector


In operation, the magnetic section of the hybrid is used to select ions of a particular m/z value. Por example, if a mixture of two substances gives two molecular ions, Mj and Mj, the magnetic sector is used to select one or the other. The selected ions collide with gas in the collision cell (Pigure 21.1), and some of them decompose to yield fragment ions, say P, Pj, and P3. Thus, a stream of ions M, (some of which have not been decomposed) plus P, Pj, and F, leave the collision cell (Pigure 21.3). If this beam went straight to the single-point ion collector, there would be no separation into the individual m/z values, and it would not be possible to measure their m/z values. However, by pulsing the pusher electrode placed just after the collision cell, a section of the beam is sent orthogonally down the TOP analyzer tube, which does separate them according to m/z value, which is related to the length of time they take to reach the multipoint microchannel plate collector (Pigure 21.1). Therefore, molecular ions and fragment ions are obtained in this MS/MS mode.  [c.160]

A fuller description of the microchannel plate is presented in Chapter 30. Briefly, ions traveling down the flight tube of a TOF instrument are separated in time. As each m/z collection of ions arrives at the collector, it may be spread over a small area of space (Figure 27.3). Therefore, so as not to lose ions, rather than have a single-point ion collector, the collector is composed of an array of miniature electron multipliers (microchannels), which are all connected to one electrified plate, so, no matter where an ion of any one m/z value hits the front of the array, its arrival is recorded. The microchannel plate collector could be crudely compared to a satellite TV dish receiver in that radio waves of the same frequency but spread over an area are all collected and recorded at the same time of course, the multichannel plate records the arrival of ions not radio waves.  [c.197]

All mass spectrometers analyze ions for their mass-to-charge ratios (m/z values) by separating the individual m/z values and then recording the numbers (abundance) of ions at each m/z value to give a mass spectrum. Quadrupoles allow ions of different m/z values to pass sequentially e.g., ions at m/z 100, 101, 102 will pass one after the other through the quadrupole assembly so that first m/z 100 is passed, then 101, then 102 (or vice versa), and so on. Therefore, the ion collector (or detector) at the end of the quadrupole assembly needs only to cover one point or focus for a whole spectrum to be scanned over a period of time (Figure 28.1a). This type of point detector records ion arrivals in a time domain, not a spatial one.  [c.201]

There are two common occasions when rapid measurement is preferable. The first is with ionization sources using laser desorption or radionuclides. A pulse of ions is produced in a very short interval of time, often of the order of a few nanoseconds. If the mass spectrometer takes 1 sec to attempt to scan the range of ions produced, then clearly there will be no ions left by the time the scan has completed more than a few nanoseconds (ion traps excluded). If a point ion detector were to be used for this type of pulsed ionization, then after the beginning of the scan no more ions would reach the collector because there would not be any left The array collector overcomes this difficulty by detecting the ions produced all at the same instant.  [c.209]

Other types of mass spectrometer can use point, array, or both types of ion detection. Ion trap mass spectrometers can detect ions sequentially or simultaneously and in some cases, as with ion cyclotron resonance (ICR), may not use a formal electron multiplier type of ion collector at all the ions can be detected by their different electric field frequencies in flight.  [c.212]

The reflectron is a device that uses an opposing electric-field gradient to reverse the direction of travel of ions as they near the end of the flight tube. At some point in the reflectron, the ions are stopped and then accelerated back out, returning through the flight tube or along a slightly different trajectory. Where the return path is different, the trajectory of the ions is approximately V-shaped the top of one leg of the V is the position of the pusher electrode, and the top of the other is the position of the ion collector (a microchannel plate detector).  [c.404]

Each element of an array detector is essentially a small electron multiplier, as with the point ion collector, but much smaller and often shaped either as a narrow linear tube or as somewhat like a snail shell.  [c.409]

Alternatively, the ions in a mass spectrometer can also arrive at a multipoint collector as a temporally dispersed beam. Therefore, at any point in time, all ions of the same m/z value arrive simultaneously, and different m/z values arrive at other times. Ail elements of this collector detect the arrival of ions of one m/z value at any one instant of time. This type of detector, which is also an array, is called a microchannel plate collector of ions.  [c.410]

Each element of an array or a microchannel plate ion collector is essentially an electron multiplier, similar in operation to the type used for a point ion collector but very much smaller.  [c.410]

A vibrating conveyor fluid bed dries while conveying particulate material on a screen-covered perforated deck. Gas is blown up through the material as it is conveyed mechanically and a particle dispersion much like that in a shallow fluid bed may be produced. Both mechanical and fluid energy contribute to fluidization. To minimize dusting, a lower fluidizing velocity is used than in a stationary fluid bed. Bed depth rarely exceeds 50 mm because mechanical energy is not transmitted through deeper beds effectively. Mechanical conveying encourages plug flow and several temperature stages may be incorporated in a single conveyor, but maximum material residence time is about 5 min. As in stationary fluid beds, all feed material must be nonsticky and free-flowing. Pneumatic Conveyors. Conveyors are adapted for drying by heating the conveying gas, although for drying, gas-to-material ratios must be greater than those sufficient for conveying (qv). Particle residence time is only a few seconds in fact, most drying takes place near the feed point where the velocity difference between gas and material is the greatest. Conveying tubes rarely need to be over 10 diameters long. For drying accompanied by deagglomeration, two or three pneumatic conveyors may be used in series and dry product may be recycled to the first stage for feed conditioning. Figure 16 shows a simple dryer consisting of a venturi feeder, tube, and product collector. Knife, hammer, and roUer mills are alternative feeding devices. A paddle conveyor, its paddles inclined to retard material flow, may be installed in place of the venturi to increase residence time and enhance dispersion. Conveying tube gas velocity is usually 25—35 m/s venturi throat velocity is 100—140 m/s. The conveyor is a low power fluid energy mill and particle attrition may be severe. This dryer is single-stage and cocurrent, like the cocurrent rotary, but has much lower residence time. Indirect heat may be combined with direct heat by jacketing the conveying tube.  [c.251]

Temperature Temperatures are limited by the type of filter media and sealant used in the cartridges. Standard cartridges utilizing paper filter media can accommodate gas temperatures up to about 95 C (200°F). Cartridge filters utilizing synthetic, nonwoven media such as needle-punched felts fabricated of polyester or Nomex can withstand temperatures of up to 200°C (400 F) with the appropriate sealant material. Spray coolers or dilution air can be used to lower the temperature of the pollutant stream. This prevents the temperature limits of the filter media from being exceeded. Lowering the temperature can result in higher humidity of the pollutant stream. Therefore, the minimum temperature of the pollutant stream must remain above the dew point of any condensable in the stream. The cartridge collector and associated ductwork should be insulated and possibly heated if condensation may occur.  [c.412]

A variety of fuel cells has been developed for terrestrial and space appHcations. Fuel cells are usually classified according to the type of electrolyte used in the cells as polymer electrolyte fuel cell (PEFC), alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), and soHd oxide fuel cell (SOFC). These fuel cells are Hsted in Table 1 in the approximate order of increasing operating temperature, ranging from - 80° C for PEFCs to - 1000° C for SOECs. The physicochemical and therm omechanical properties of materials used for the cell components, ie, electrodes, electrolyte, bipolar separator, current collector, etc, determine the practical operating temperature and useful life of the cells. The properties of the electrolyte ate especially important. SoHd polymer and aqueous electrolytes are limited to temperatures of ca 200°C or lower because of high water-vapor pressure and/or rapid degradation at higher temperatures. The operating temperature of high temperature fuel ceUs is determined by the melting point (MCEC) or ionic-conductivity requirements (SOEC) of the electrolyte. The operating temperature dictates the type of fuel that can be utilized.  [c.577]


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