Split Ratio setting in 7890 B GC:

Question

Cannot enter split ratio of 50:1. During input, the split limit displayed 0.1 to 25, where column flow is 7.525 ml/min and a split flow of 20 ml/min. Column dimensions are 30 x 530 and 3 micron. Within this specification, how can I set a 50:1 split ratio?

CMZainea · Answer

Hello g.rabbani579 , 
 
 There is some information missing in here, particularly what type of inlet are you using, and what type of gas. However, based on the nature of the problem, I will assume that the carrier is N2 and the inlet is either MMI, SSL or PTV. 
 The reason I am making this assumption is because 50:1 ratio would put you at 376.25 split flow. Adding up the column flow and septum purge, the total flow would be 386.775 mL/min (if using an SSL inlet). From the data sheet of the 7890B, the maximum total flow* allowed for N2 for SSL, MMI and PTV inlets is 200 mL/min. In your case, the total flow would be higher than the maximum allowed flow. This would explain why it would let you do a 25:1 split (total flow = 198.65 mL/min -if using an SSL inlet-, which is below the 200 limit). 
 5991-1436EN_5989_5672.qxd (agilent.com) 
 
 Let me know if my assumptions are correct and if this makes sense.

Split Ratio setting in 7890 B GC:

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