Continuous beam

A further important property of the two instruments concerns the nature of any ion sources used with them. Magnetic-sector instruments work best with a continuous ion beam produced with an electron ionization or chemical ionization source. Sources that produce pulses of ions, such as with laser desorption or radioactive (Californium) sources, are not compatible with the need for a continuous beam. However, these pulsed sources are ideal for the TOF analyzer because, in such a system, ions of all m/z values must begin their flight to the ion detector at the same instant in... 

The most familiar gas laser is the helium—neon laser (23,24). Sales of commercial helium—neon lasers exceed 400,000 units per year. The helium—neon laser is a compact package that produces a continuous beam of orange-red light. The inside diameter of the tube is commonly around 1.5 mm. The output of helium—neon lasers available commercially ranges from a fraction of a milliwatt to more than 35 mW. They have many appHcations in the areas of alignment, supermarket scanning, educational demonstrations, and holography. 

A double beam instrument splits the electromagnetic radiation into two separate beams, one for the reagent blank, and the other for the sample. There are two ways to do this. The first method uses a mirror that is half silvered and half transparent. As shown in Fig. 5.17 this results in a continuous beam of light for both the sample and reagent blank. 

Fig. 5.17. Essentials of a double beam instrument in space. This is characterized by two continuous beams of light.

There are also only a limited number of available slots in geosynchronous orbit where a satellite would be able to continuously beam power to a specific receiver. In areas with plenty of sun and available land, satellites may not compete with generating solar power locally. There would be more demand for beaming solar power to locations that couldn t generate it otherwise. 

In the ion trap technology, ions are captured in three-dimensional electric fields. The continuous beam of ions fills the trap up to the limit of their space charge. When additional electric fields are applied, ions are ejected sequentially and detected. Accumulation of ions in the trap results in high sensitivity for these instruments. The trap can be operated in MS and MS/MS modes. In the latter, the ions of interest are maintained in the trap, whereas the other ions are excluded. Sequential fragmentation steps can be performed to generate MSn spectra, highly valuable for structural characterization studies. 

In general the commercial TOP instruments have two detectors one for the linear mode and one for the reflectron mode. The combination of MALDI with TOP is ideal because both techniques are pulsed techniques. However, it is also possible to arrange a continuous beam as generated by electrospray ionization. Por that purpose orthogonal acceleration was developed [65]. The ion beam is introduced perpendicularly to the TOP and packets are accelerated orthogonally (oa-TOP) at similar frequencies improving the sensitivity. While a packet of ions is analyzed, a new beam is formed in the orthogonal acceleration. 

Figure 11.74 shows a similar approach to the measurement of a continuous beam of volatile and semivolatile particles with diameters as small as 0.02 /im (Tobias et al., 1999). Upon exiting the aerodynamic lensing system, the particles enter a small ( 0.1 cm3) cell whose temperature can be regulated and is typi-... 

FIGURE 11.74 Schematic diagram of aerosol particle mass spectrometer for measurement of composition of continuous beams of volatile and semivolatile particles (graciously provided by P. Zie-mann, 1998). 

A continuous laser operates by continually pumping atoms or moie-cules into the excited state from which induced decay produces a continuous beam of coherent radiation. The He—Ne laser is an example of continuous system. Another mode of operation is to apply an energy pulse to the system, exciting a considerable fraction into the excited state. When all these molecules or atoms are induced to decay simultaneously, intense but exteremely short pulse of coherent radiation is emitted. The ruby laser falls in this category. 

The experimental setup used by our group is shown in Figure 7-1. This apparatus consists of a molecular beam source coupled to a chamber housing the quadrupole mass spectrometer. The continuous beam source consists of a Campargue-type nozzle, an expansion chamber, and a collimation chamber. The nozzle assembly itself is mounted on a micrometer and is fitted with a gas handling line which... 

The earth is provided with two sources of energy, the capital resources deposited within the earth during its formation and the income resource continuously beamed onto the earth from the sun. Both are essential to human existence. 

Orthogonal injection provides a high-efficiency interface for sampling ions from continuous beam to a TOF analyser. The TOF analyser allows simultaneous transmission of all ions and therefore all the ions formed are analysed. However, the duty cycle is far from 100 % for the oa-TOF spectrometer and it is lower than for the TOF spectrometer. This is due to the orthogonal accelerator that samples to the analyser only a part of the ions produced in the source. The duty cycle, despite this fact, is between 5 and 50 %. This is a considerable improvement over the conventional techniques described for coupling a continuous source to a TOF spectrometer. 

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