INFICON Explorer Portable Gas Chromatograph - Manual (Page 305)

Explorer Operator Manual
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In addition to container effects, there are a variety of other issues regarding sample
storage, processing and preparation that can compromise the accuracy of the
concentration measurement.
Adsorption
Another potential instrument source of error is sample adsorption by Explorer’s
analytical system. If this occurs, it will typically be seen as an increase in peak
area upon repeated sampling of the component, even after the instrument has been
in operation for many hours. The effect is usually concentration dependent, as
higher concentrations will supply the demand of a limited number of adsorption
sites without a significant percentage of sample loss.
Explorer has been designed to minimize adsorption effects by heating the
analytical system. However some compounds may still be problematic at low
concentrations.
Detector Response Drift
Detector response drift is caused by drift in the effective UV lamp intensity over
time. Although
Explorer maintains a constant visible lamp intensity, it is
possible that the ionizing spectral lines, located outside the visible range, shift in
intensity over time.
Detector response drift will manifest itself as an effect that typically occurs over a
longer time period than adsorption and which is not as compound specific as
adsorption. Also, it is not affected by the frequency of sampling, unlike adsorption
phenomena. Calibration is recommended when the detector response has changed by
greater than 10%. This will be approximately 8 hours.
The instrument must be calibrated when Explorer is turned on and should be
calibrated at 8 hour intervals thereafter. We recommend that you perform the
calibration under similar temperature and humidity conditions as that of the
sample.