INFICON Explorer Portable Gas Chromatograph - Manual (Page 330)

Explorer Operator Manual
328
Precolumn backflushing reduces total analysis time in Explorer. It is not necessary
to wait for the longer retained components that are not required, to pass through
the analytical column. Precolumn backflushing also increases analytical
confidence by reducing the possibility of peaks from an earlier analysis eluting
during a later analysis.
Column Selection
In a GC, the types of sample components which can be separated from one another
are dictated by the type of GC column used. Some column types are suited to light
gases, others to heavier vapors, and yet others to polar vapors. For flexibility in the
types of compounds which can be analyzed in a GC, it is necessary to have several
different types of columns installed so that the optimum column can be selected for
the particular analysis. This is typically done by having you, the GC user, remove
and replace columns within the GC instrument.
In Explorer, four columns are installed and kept ready for use. Refer to the user notes
supplied with your assay for detailed specifications of the columns installed in your
instrument and how to use the columns for your application.
In TVOC mode, no gas chromatography is performed on the sample. Instead, the
sample is introduced into a stream of carrier gas and carried directly to the detector.
All separating columns are bypassed. The detector response is a single peak which
represents the composite of all detectable compounds in the sample.
Photoionization Detector
The photoionization detector (PID) consists of a detector cell through which the
column effluent flows, and a lamp that directs ultraviolet (UV) light into the cell.
In
Explorer, the lamp is an electrodeless discharge tube, and is made to light using
a high-frequency (HF) driver circuit.
The lamp contains low pressure gas into which the high frequency energy is coupled
through an antenna wrapped around the lampholder. The HF driver circuit is
controlled by
Explorer's microprocessor based on a feedback signal from a light
sensor on the HF driver circuit board.