Chromatography Forum

Dear all,

we have a situation I cannot understand and I hope you can help me.
Our machine is an Agilent 8890 and we would like to perform a splitless injection.
To have a splitless injection I set the Purge Flow to Split Vent to 0 mL/min but when I start that, the GC can not establish the correct flow of 1 mL/min but it stays below at around 0.8 mL/min. Later it gives a pressure error.
Do I have to enter a flow for the Purge Flow to Split Vent? If yes, I believe that I cannot really perform a real splitless injection...
Thanks for your help.

Christian

That split flow setting is for the flow rate after the splitless injection. The purge time right next to that flow setting is how long you want your injection to last, we generally run 0.5-1 min.

ChrisT,

You have to congfigure the inlet as splitless first. Then the split flow and the time are as noted above, they turn on after ~ 0.6 minutes at something like 50 ml/min. But you have to tell the inlet splitless first.

Best regards,

Aicmm

To add to this conversation, since you're using an Agilent, and optimal purge time will depend on several variables, the "pressure flow calculator" GC calculator can recommend an optimum purge time. Just enter the values for your instrument and method.

In a splitless injection mode, the purge flow to the split vent is typically set to 0 mL/min to ensure that the entire sample is transferred to the column. However, you mentioned that when you set the purge flow to 0 mL/min, the GC is unable to establish the correct flow of 1 mL/min and instead stays around 0.8 mL/min, leading to a pressure error.

In a splitless injection mode, the purge flow to the split vent is typically set to 0 mL/min to ensure that the entire sample is transferred to the column. However, you mentioned that when you set the purge flow to 0 mL/min, the GC is unable to establish the correct flow of 1 mL/min and instead stays around 0.8 mL/min, leading to a pressure error.

Agilent software does this by default, setting the post inject purge flow to 0 mL/min was why the instrument was erroring out. Bad info my guy.

The pressure error you are encountering may be due to a lack of purge flow to the split vent, which is needed for controlling the inlet pressure in the system. Even during a splitless injection, a very small purge flow (usually around 10-20 mL/min) is often required to maintain proper inlet pressure regulation and avoid overpressure conditions. Basketball Stars

The splitless transfer to the column is achieved by re-routing the total gas flow, not by changing its flow rate. As others have said- the instrument will take care of it once you have selected a splitless injection.