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4.1.3 Sample Injector
The sample injector, also known as simply the injector, injects the sample into the
stream of carrier gas.The sample injection must assure a precise injection of sample into
the flow of the carrier gas.
In principle the amount injected must be very precisely controlled, both in volume,
pressure, temperature and flow (to avoid viscosity effects) to guarantee a high level of
repeatability of the analytical results, but in practice the normalisation of the measured
concentrations will compensate for a large part of the fluctuations of these parameters.
However, to reach repeatability for the heating value below 0.01 %, these parameters do
have effect and need to be controlled to a high degree.
The used MEMS technology allows a fundamental improvement of the sample injection
quality compared to the traditional fine-mechanical technologies used for most of the
current process GC’s on the market. The picture below shows a typical MEMS sample
injector, etched in silicon channel, with membrane valves to control flow directions.
This injector allows for a very precise control of the injection volume and temperature,
on a remote base.
Figure 4.4: MEMS Sample Injector
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