Adjust back pressure on HTI to get a stable EA signal
Problem
The elemental analyzer does not integrate peaks reliably, baseline corrections are not possible due to changing back pressure when trapping vs. not trapping.
Solution
Set up the exhaust flow correctly by using a clamp on the exhaust line of the HTI
With the EA running in standby and V2 open in the HTI software, write down the current TC detect. value, e.g. 885
Blue arrows show EA exhaust pathAt the HTI software, open V3 and V5 and also switch V2 (V1 implicitly) so that the EA exhaust flows through the trap and is vented to atmosphere past V5. Allow the TC detect. signal to settle for a minute. Write down the new value of the TC detect.
If the TCD value is lower in this configuration than in step 1, proceed. Otherwise, something is not set up correctly.
Close V3 and V5 and switch back V2 so the exhaust is vented to atmosphere directly at V2. Start tightening a clamp around the exhaust capillary after V2. Do this until you can see a significant change in the detector signal that resembles the detector signal under step 2. If necessary, loosen the clamp a bit to allow more flow again.
Tighten clamp screws incrementally and wait several seconds after each adjustment for the TCD reading to stabilize. As you approach the value, make very small adjustments as it is easy to overshoot the value.
After a successful adjustment of the exhaust capillary, the detector signal of the EA will remain within about 20 units with the flow going through the exhaust vs. going through the trap.
Either leave the clamp on, or deform the tube to a point where it will stay at the target TCD reading without the clamp (removing the clamp usually raises the TCD reading so it requires additional trial and error to reach the ideal deformation.)
In case you overshoot the exhaust crimping you can optionally use the pliers to slightly undo the deformation.
