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Can I increase septum purge flow instead of split flow without diluting sample?

Question asked by chemist23 on Jul 15, 2020
Latest reply on Jul 16, 2020 by james_jenkins



I am having issues with GC-MS using S/SL inlet connect to headspace unit. In order to maintain a minimum total flow of 20mL/min, I need to maintain a minimum split ratio of 11:1. In order to detect my sample peaks I need to run at a split ratio as low as possible, close to 3:1. Problem is if I operate at lower split ratio's than 11:1, I cannot maintain a total flow of 20 mL/min. 


Is it feasible to increase the septum purge flow to compensate for a low split ratio without diluting the injected sample? What exactly does the septum purge flow do? It's normally set at 3 mL/min. What will happen if I set it to 30 mL/min?


I also notice my N2 check readings are higher when connected to the headspace S/SL back inlet then the direct injection S/SL front inlet at equal split ratio's. Is this typical? james_jenkins