INFICON HAPSITE ER Chemical Identification System - Manual (Page 442)

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HAPSITE ER Operating Manual
14.7 Valves and Sequences
The SituProbe follows a fixed sequence of events to volatilize, transfer, and collect
the water sample VOCs for HAPSITE analysis. The order of these events cannot
be changed, however the duration of each event can be adjusted (within ranges)
to meet the application’s analytical requirements.
The SituProbe accessory module contains heated valves and tubing to direct
sample and Nitrogen flows in the process of collecting and transferring sample
VOCs. The source of Nitrogen used by the SituProbe is either the onboard canister
mounted in the module or a pressure regulated bulk cylinder supplied through the
quick-connect at the back of the module. Nitrogen is not provided by the HAPSITE
for SituProbe operations.
Before the method will start, the Sampling Probe must be properly immersed in the
water sample, as sensed by the conductivity electrodes and indicated by the LED
display on the front of the module.
14.7.1 Headspace
CAUTION
Without a headspace, the instrument could pull water
into the system.
The first operation is to create a headspace in the sampling probe. For five
seconds, a flow of nitrogen is directed from the SituProbe module, through the
sampling line and through the center of the probe head. The sample water level is
pushed down to the upper holes in the purge tube, creating the headspace volume.
14.7.2 Purge
Valves in the SituProbe module are set to provide Nitrogen to the long tube at the
bottom of the probe purge tube. Simultaneously, the HAPSITE sample pump starts,
and the Nitrogen purging through the sample is drawn out through the center
opening of the probe head, through the SituProbe module, and to the HAPSITE.
The Nitrogen purge flow rate must exceed the HAPSITE’s sample pump flow rate
to maintain the headspace. As a safety feature, if the headspace decreases and
the water reaches the upper conductivity electrode, a valve in the SituProbe
module will open to prevent water from being drawn into the system.
During sample purging, the SituProbe provides a continuous flow of sample VOCs
to the HAPSITE. The HAPSITE’s configuration determines whether the VOCs are
simply purging the sample pathway or are being collected on a Concentrator. When