Sequence 4
For sequence 4, before the second sampling stage, the filter, oven walls and transfer lines must be well cleaned.
The oven and filter are cleaned, first, by extending oven heating by 1 min in order to complete filter outgassing (filter temperature is 600°C at the end of sequence 3's last transfer). Immediately after, the oven is filled to 2.5 bar within 3 s by activating the oven's pressure control loop to open Vl. Then, the oven is vented by opening VT for about 6 s, reducing the pressure down to ambient atmospheric.
Cleaning the transfer lines downstream of V2 is achieved first by switching on heaters HV2 and HPl (plus PTL), set at the maximum 120°C, for 90 s. Then, a fill-vent phase is started for the oven and transfer lines by :
- 1. switching on the oven's pressure control loop (filled at a maximum 2.7 bar) while valve V2 is opened for approximately 3 s;
- 2. venting the two circuits when reducing the internal pressure to the external level at the two ends. The oven is vented by opening VT (6 s), while the transfer lines downstream of V2 are vented through GCMS by opening VAA (few seconds).
This fill-vent operation is repeated once. Thre is no background analysis from the MS in order not to contaminate the GCMS instrument unnecessarily. At the end of sequence 4, ACP is ready for a second sampling sequence.
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