Recently I came across a situation where I wanted to make a series of constant flow GC-FID runs, during which, the inlet pressure would increase from 2 to 6 PSI over the temperature program. I also wanted to use split injection with a split ratio of at least 20:1, in this case that translated to a split vent flow of about 150 mL\/min.<\/p>\n\n\n\n
I realized that I would be pushing the lower limit of reliable inlet pressure control but those parameters should be within the range of a (relatively) modern EPC controlled HP 6890 GC. Of course, as I installed the column and got to work it was clear that something wasn’t right.<\/p>\n\n\n\n
The inlet pressure would rise above the set point and stay there completely stable, like there was some sort of constant offset preventing the GC from becoming ready. I noticed that as I increased the split flow the real-time inlet pressure would rise further and further above the set point.<\/p>\n\n\n