GC7890 Splitless injection mode

Question

Hi, 
 First, I don't have much experience with Splitless injections. I have a method, it is splitless injection mode, the liner is 4mm ID and 78.5mm length, the column flow rate is 8ml/min, and the septum flow is 3ml/min. Is it necessary to set up the purge flow and purge time? Are the purge flow and purge time critical conditions or minor? Can these two conditions be altered during the sample analysis when the method is validated? We run the same method with the splitless on the GC model 6890, the purge flow and purge time are left blank, but the system is still working, why?

CMZainea · Answer

Hello Daisy_GC , 
 
 Thank you for your question. The purge flow essentially flushes the inlet before the next injection. When you are doing splitless injections, you want to make sure that all your vaporized sample goes onto the column before turning on the purge flow. For this, you need to set up the purge time correctly (liner size divided by the split flow). For example: 
 
 If you have a liner with a .9 mL volume, and you have a flow of 1.8 mL/min, the purge time should be 0.5. These are just examples, the flow could be higher, and you can keep the purge time as 0.5. As long as the liner volume/purge flow are greater than the purge time, you are good. Otherwise, you are losing sample out the split vent (and essentially doing a split injection). 
 
 I am not entirely sure why there is a separate behaviour between the 6890 and the 7890. Is the column configured on both GCs? And are you getting any errors on the 7890?