INFICON HAPSITE ER Chemical Identification System - Manual (Page 484)

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HAPSITE ER Operating Manual
16.5.1 Contamination of the Mass Spectrometer
Contamination of the Mass Spectrometer manifold can occur every time an internal
component is changed, or vacuum is broken. This can consist of water and/or light
hydrocarbons. These will be seen in the mass spectrum even when the isolation
valve is closed. (The source of contamination is not coming from the GC module.)
16.5.1.1 Symptoms
Symptoms of contamination are a high background of water or hydrocarbons in the
mass spectrum, a high baseline in the TIC plot, or a higher than normal base
pressure. Contaminates on the Ion Source or the NEG pump will be driven off as
these components are heated. Use this heat to decontaminate the instrument.
16.5.1.2 Decontamination
Decontaminate the vacuum manifold using the Service Module. Pump for a few
hours for water or light hydrocarbons, or as long as 24 hours if the contamination
is heavy. Remember that various components of the vacuum manifold will get hot
and aid in driving off unwanted substances. Turn the Ion Source filament ON and
heat the NEG pump to 400

C when decontaminating a system. If the
contamination will not go away after a full day of pumping, the suspect component
must be removed and replaced. Remember care must be taken when handling
internal components of the vacuum system. Always use new gloves or a clean lint
free cloth to avoid contact with skin oils.
16.5.2 Contamination of the Gas Chromatograph
Contamination of the Gas Chromatograph (GC) can occur if hot heavy organic
gases are sampled, and condense in the system. These will be seen in the mass
spectrum only when the isolation valve is opened. (Background may be high after
the isolation valve is first closed, but will drop off after a few minutes.)
16.5.2.1 Symptoms
Symptoms of contamination are a high background of hydrocarbons in the mass
spectrum, or a high baseline in the TIC plot.
16.5.2.2 Decontaminate
Decontaminate the GC by moving the instrument to an area where the air is
relatively clean or connect the transfer line to a canister of a pure gas (N
2
or Air).
Flush the sampling pathway by setting up a GC method to loopfill for 5 minutes.
Repeat this method until the source of the contamination is flushed out. Heating all
temperature zones to the maximum allowable setting will aid in the cleansing of the
GC. Some compounds may become trapped at unheated locations and might
require a longer time period to be flushed out. If the boiling point of the contaminate
is greater than the maximum temperature of the heated zones, or if a liquid sample
has been pulled into the system, the GC and Transfer Line may need to be
replaced.