INFICON HAPSITE ER Chemical Identification System - Manual (Page 447)

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HAPSITE ER Operating Manual
14.10 Operating Tips
14.10.1 Reducing Background
Operator judgment is the first and best means of reducing background and
carryover contamination in the SituProbe.
14.10.1.1 Sampling Precautions
Avoid immersing the probe into an organic phase indicated by a sheen on the
surface of the water phase. Alternatively, try locating a less contaminated sampling
area or collect a sample from below the surface with a separate sampling vessel.
In addition to the analytes of interest, consider all VOCs that may be present in the
water sample.
14.10.1.2 Expected Concentration
Select a Loop or Concentrator method based on detection limit requirements.
Prepare and analyze standards within the concentration operating range of the
SituProbe/HAPSITE configuration.
When using a Concentrator method, set an appropriate "ConcFill" event time for
the expected VOC concentration range and detection limit requirements. Collecting
on the Concentrator for longer than required will unnecessarily emphasize
background interference.
Analyze clean water blanks on a regular basis to purge the system and monitor the
background level for use in interpreting sample data.
14.10.2 Nitrogen Usage
The Nitrogen supply to the SituProbe is only consumed during sample analysis.
There is no Nitrogen usage between sample runs. Nitrogen is consumed during
headspace creation, sample purging, and dry purge events. The operator has
control over the timing of the last two events. The sample purging events consume
the most nitrogen because the flow rate must exceed the HAPSITE sample pump
flow rate. Nitrogen sample purge usage can be managed in two ways:
 The "SituProbe Flow Pressure" method parameter should be set to supply an
excess of a few Nitrogen bubbles exiting the upper holes in the purge tube
during the purge event.
 Sample purge time should be set to the minimum time required to properly
purge and equilibrate the sample pathway and to collect the proper amount of
sample for concentrator methods. Experience with the analysis will determine
the correct timing.
The dry purge Nitrogen (Concentrator methods only) flow is fixed at approximately
20 mL/min, but the event time can be controlled. The amount of moisture collected
on the Concentrator during sample purging will depend on the water sample’s
temperature and the length of the "ConcFill" event. When moisture from the