Page 156 - Tandem Techniques

Page 139

The use of light pipes was introduced very early in the GC/IR development and one of the first
references to the device, is that of Wilks and Brown in 1964 [3]. Light pipes are tubes of circular or
rectangular cross-section with highly reflecting internal surfaces that are usually produced by gold
plating. The light source is moved back, so that the focus, which coincides with the entrance of the light
pipe, is transferred to the exit of the light pipe but the process is not completely efficient. Internal
reflections at the walls of the light pipe increases the 'apparent path length' by about 33%. Many modern
GC/IR systems employ light pipes to augment the IR signal, and an example of a contemporary GC/IR
tandem instrument that utilizes light pipe amplification is that manufactured by the Perkin Elmer
Corporation. A diagram of the optical system of the Perkin Elmer instrument, which is typical of many
contemporary GC/IR tandem systems, is shown in Figure 4. 5.

Figure 4.5
The Optical System of the Perkin Elmer GC/IR Tandem Instrument
Courtesy of the Perkin Elmer Corporation