INFICON CMS5000 Monitoring System - Manual (Page 16)

1 - 2
IP
N 07
4-
50
8-
P1
C
CMS5000 Operating Manual
1.2 Gas Chromatograph
The gas chromatograph (GC) performs a time separation of the sample
compounds. The separation order is primarily based on increasing compound
boiling point.
Argon is used as the carrier gas to transport analytes through a 100%
dimethylpolysiloxane, 0.32 mm id, 30 M, 4.0 µm (or equivalent) column. The inside
of the column is coated with a thin layer of material known as the stationary phase.
The stationary phase selectively attracts components in a sample mixture. The
mixture of sample compounds in the argon gas, also known as the mobile phase,
interact with the chemicals of the stationary phase. The chemicals which spend the
least time partitioned in the column will elute (exit) off the column first.
The time taken by an individual compound to travel into the system until the
compound elutes from the column is referred to as the retention time (RT). If the
GC conditions remain constant, the same compound will elute from the column at
nearly the same retention time for each injection.
The performance of the column is affected by temperature, therefore, the column
is housed in a temperature controlled oven. The oven is programmed to increase
the temperature gradually (called ramping) to improve compound separation while
decreasing analysis time. As the temperature increases, the compounds with the
lowest boiling points will elute first with the standard non-polar phase coated
column installed.
A chromatogram of eluting organic gases from the gas chromatograph is plotted as
a function of time from the injection the compound mixture. The chromatogram
depicts the separation of the various compounds from each other by the action of
the gas chromatograph, as described above.
1.3 Micro Argon Ionization Detector (MAID)
The Micro Argon Ionization Detector (MAID) is sensitive to organic compounds
having an ionization potential of 11.7 eV or lower, which includes halomethanes,
haloethanes, carbon tetrachloride and 1,1,1-trichloroethane. The CMS5000 can
detect these compounds, as well as other hydrocarbons, to parts-per trillion (PPT)
levels.
The MAID uses argon as a carrier gas. When argon flows over a nickel-63 (Ni-63)
source, argon atoms are energized to an excited, metastable state, while other
argon atoms are ionized. The excitation energy of argon is approximately 11.7 eV.
Ar  Ar* (Energized to excited state)