Inficon 3000 Micro GC, Operating Manual

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3000 Micro GC Operating Manual
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Separation: As the sample gas enters the column, its component gases are
separated based on their retention or adsorption property with the column
stationary phase material. The longer the component gas is retained by the
column, the later it will elute from of the column for detection. Components may
be separated based on size, polarity, or boiling point, depending on the column.
3
Detection: After column separation, the sample gas enters the Thermal
Conductivity Detector (TCD). 3000 Micro GC employs a
Microelectromechanical systems (MEMS) TCD which operates on a
Wheatstone bridge circuit. The carrier gas enters the TCD via two pathways,
the reference path and the analytical path. The reference path contains only
carrier gas. The analytical path contains carrier gas and sample gas. The TCD
measures the difference in thermal conductivity between the carrier gas
reference and the sample gas components.
For example, the thermal conductivity of helium carrier gas at 300 K is
157 mW/m K. The thermal conductivity of methane sample gas at 300 K is
34 mW/m K.This difference is picked up by the Wheatstone bridge circuit,
generating signal response to the sample component eluted. See
Figure 3-9 .
Figure 3-9 Wheatstone bridge circuit
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