The split ratio you mention is not how we would suggest you use the split/splitless inlet. Typically the inlet needs a total flow of around 20 ml/min to function properly. That is the flow it was designed around. You can get away with lower but it is not suggested. Perhaps you could reply with the complete method parameters for the GC and headspace that you are using and that may give us a hint as to what is happening. My first thought , if this was an older G1290A headspace would be that flow was being added from the headspace itself using its pressure regulator. I am not familiar with the 7697A so method parameters would help and perhaps provide an answer.
Here’s the instrument method. Again, we can get it to run on only one instrument. It works on a 6850/7697A setup but not on a 7890/7697A setup or another 6850 with a liquid injector (GC parameters only). I’m befuddled. The GC/HS setup on which this method works must have crazy good pressure transducers.
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This doesn't really answer why, I have attached the flow recommendations from our factory. In reviewing the method parameter I am surprised it works.
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Nice post. I agree with you and James that the method setting is sub optimal. Some reasons it works on one system and not others could be due to the instrument configuration and installed columns.
- HS carrier gas flow mode. The 7697A HS systems have options which enable the HS to control the carrier gas and therefore the "GC" split ratio is not really the split ratio applied to the flow.
- A 0.53um ID column with a flow rate of 4mL/min gives a relatively larger split flow 0.8mL/min under those settings (split ratio 0.2:1) then other columns. If on the other systems you were running narrower bore columns or lower flow rates the split flow would be much less as in the example given in the letter posted by James. If you raise the column flow rate and therefore inlet pressure the other systems may be able to do it too...
- Leaks may cause one system to be better or worse then others.
- Firmware and driver versions may all differ.
- Split vent trap or line blockages/restrictions.
- As the letter states, carrier gas line pressure too low or high
- As the letter states, EPC "zero" values.
Hope that helps.
Marking this as assumed answered, if there are still points of discussion, by all means continue to post and we are happy to continue the discussion .