The Development of an Airborne Gas Chromatograph
INSTRUMENTATION
An airborne GC system prototype has been constructed in Leeds for the in flight analysis of non-methane
hydrocarbons onboard the UMKO C-130 aircraft. It's response to a variety of different species has been characterized.
The airborne gas chromatographic system consists of methods for trapping and reconcentrating the air
samples, for separating the components of the sample and for detection of the components.
The trapping and reconcentration of low concentration air samples is attained via the use of stainless
steel tubes packed with an adsorbent onto which the air sample is pumped. The collected sample is then
thermally desorbed, in a stream of helium, on to a gas chromatographic column where separation of the
desired hydrocarbons is achieved. The eluted components are detected using a
Helium Ionisation Detector, with 1% argon in helium
as the discharge gas. For more info on the HID visit the VALCO website
There are several advantages to using the HID as the detector in the airborne GC system:
- Firstly, the HID can be utilised in any orientation without loss of performance, unlike the FID,
which is the standard detector for the analysis of hydrocarbons. As a consequence, the HID can be made
to fit into any available space in the system, even if it has to be aligned at an angle. It also means
that if the aircraft were to bank, altering the orientation of the detector, the output of the detector
would not be influenced.
-
The robustness of the HID also makes it particularly suitable for use on board an aircraft, because
knocks to or sudden movements of the detector do not affect it’s performance. This provides a clear
advantage over the FID which, if knocked, causes a sharp spike to appear on the resulting chromatogram.
-
The only gas needed to run the HID is helium - which can also be used as the carrier gas to sweep the
sample through the column. As a result, only one cylinder of a relatively safe gas need be taken onto
the aircraft hence saving space. The FID requires two gases, hydrogen and air, in addition to the
carrier gas. This means not only would 3 cylinders have to accompany the GC instrument on to the aircraft,
but there is also a significant safety hazard with hydrogen being used on an aircraft due to the risk of explosion.
-
The non-selectivity of the HID means that oxygenated species of interest, such as acetone, are able to
be analysed and it means that the need for system modification would be avoided if the species of interest were to change.
We have a few photos of the instrument in its current developmental stages.....here
This page was originally constructed by Jude Davies
Last modified by Jim McQuaid on Sat Nov 02 12:49:36 2002