Page 361 - Tandem Techniques

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0.05 mm thick). The belt then transports the film to the vacuum locks and on the way is heated by an
infrared heater to facilitate evaporation of the solvent. The remaining solvent is removed during passage
through the vacuum-locks so that only about 10 g/sec of the solvent actually enters the mass
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spectrometer.

Figure 9.12
The Belt GC/MS Interface
The first interface pump removes air at a rate of 500 1/min and the second at about 300 1/min. The
pressure in the first vacuum-lock is maintained at between 1 to 20 torr, and that in the second vacuum-
lock between 0.1 to 0.5 torr. As a consequence the mass spectrometer source can be easily maintained
at a pressure of about 10 torr. Flash vaporization of the solute is achieved by radiant heating, and
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occurs in a small chamber that butts directly onto the solid probe entrance to the ionization chamber.
The sample vapor passes through a small hole in the chamber wall directly into the ion source. The
flash heater is either a Nichrom coil or a quartz heater tube. In a similar manner to the wire transport
interface, the slots in the vacuum-locks are made of sapphire strips to prevent abrasion. An example of
the use of the belt interface to monitor the separation of a pesticide mixture is shown in Figure 9.13.