HPQ2-IP SP101009.102 – 10 October 2012
MKS Instruments, Spectra Products
26
7.2 Maintenance of Your Analyser
Most, if not all, quadrupole analysers have areas of inherent weakness requiring
periodic maintenance. This should be viewed as similar to automobiles which from
time to time require oil changes etc. to protect the performance of the engine. Just
like the automobile the frequency with which this work has to be carried out
depends upon many factors such as the number of miles driven, the climate, the
average length of journey and the speed at which the vehicle is usually driven.
Similarly with quadrupole analysers the type and cleanliness of the vacuum system,
the hours of operation and the type and pressure of sample being analysed play a
large part in determining the maintenance frequency. Apart from these
considerations there are times when the analyser will require maintenance and
these are when "accidents" happen i.e. when someone vents the vacuum system to
air with the filament still switched on or when someone forgets to turn on the water
cooling for the oil diffusion pump etc. These occurrences only vary in the magnitude
of the disaster that ensues.
Routinely there is only one area of the analyser that requires any maintenance. This
is the ion source. The ion source contains two filaments, only one of which will be in
use at any one time. The filament is heated to approximately 2000 deg K at which
temperature it emits electrons which are used to produce the ions required by the
quadrupole filter. At this high temperature there are two deleterious effects.
The filament material slowly evaporates and condenses upon the surrounding
surfaces. This effect is extremely slow but would require from time to time the
cleaning of the surrounding source plates and ceramics and the replacement of the
filaments.
The second effect is similar to the first except that the vacuum under which the
source is operating has either a high oxygen or water content. Then, instead of
metal being deposited upon the surrounding source plates a layer of metal oxides is
deposited. These, being insulators, have a far more noticeable effect upon the
performance of the source and therefore a more frequent cleaning program should
be undertaken.