INFICON HAPSITE ER Chemical Identification System - Manual (Page 33)

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HAPSITE ER Operating Manual
The inside of the column is coated with a thin layer of a material known as the
stationary phase. The stationary phase is a chemical which can selectively attract
components in a sample mixture. The mixture of sample compounds in the mobile
phase interact with the chemicals of the stationary phase. The chemicals which
have the fastest interactions will elute (exit) off the column first. The HAPSITE also
utilizes a temperature programmable GC. 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. More selective columns may be ordered for specific applications.
The time taken by an individual compound to travel from injection 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.
An important part of the operation of the HAPSITE is the use of Internal Standards.
They verify the performance of the gas chromatograph, as well as, the tuning and
sensitivity of the mass spectrometer. The internal standards are two volatile
organic gases at low concentrations which are added to the sample inlet flow. The
internal standards’ retention times and responses are used as references for
instrument performance.
Figure 1-2 is a graph of eluting organic gases from the gas chromatograph that is
plotted as a function of time from the injection of a pulse of mixed compounds. The
graph demonstrates the separation of the various compounds from each other by
the action of the gas chromatograph, as described above. This plot is called a Total
Ion Chromatogram (TIC).
Figure 1-2 Total Ion Chromatogram