INFICON Explorer Portable Gas Chromatograph - Manual (Page 328)

Explorer Operator Manual
326
Library retention times and sensitivities are updated whenever Explorer is
calibrated. Explorer also calculates the new retention time to old retention time ratio
for each library compound in the calibration gas. If a library compound is not
present in the calibration gas,
Explorer updates its retention time by multiplying it by
an average calculated from compounds in the calibration gas.
Sample Introduction
Samples can be introduced into a GC either automatically or manually.
Explorer accepts air and gas samples both ways.
If you have a large volume of sample available, as is usually the case in ambient air
sampling, then automatic sample injection is the easiest means of introduction. This
is done using
Explorer's internal sampling pump and sample loop. When the sample
pump is on, the sample is drawn in through Explorer's sample in port, then through
a fixed volume called a sample loop, then through the pump to be vented through
the pump out port. The sample loop has gas switching valves at either end of it.
Once the sample loop is full of sample gas, the pump stops and these valves switch
to connect one end of the loop to the carrier gas supply and the other end of the
loop to the beginning or head of the GC column. Carrier gas then sweeps the sample
from the loop onto the column for analysis. Once the sample has been injected, the
carrier gas flow is again switched, this time to bypass the loop and continue to feed
the column.
Although the sample loop volume is fixed in Explorer, it is possible to inject only a
part of the loop volume. This is done by switching the carrier gas to bypass the
loop before the entire loop volume has been swept onto the column.
To use automatic sample loop injection, you must have sufficient sample at
atmospheric pressure available for the sample pump to draw through the sample
loop and connecting tubing. If you have a only a limited amount of sample available,
such as headspace in a vial above a soil or water sample, then manual sample
injection is required. This is done using a gas tight syringe and
Explorer's injection
port.