Chromatography Forum

I am trying to set up a 5890 gc. I have the manual and a lot of notes from previous lab employees/students. When running in the split mode, I need to know a 'desired head pressure' to set everything up properly. Unfortunately I can't find an actual value for the desired head pressure in the notes that I have. One person did write down 'pressure will be much higher when using with a new column'. That is all I have to go on.

We want to run for long chain FA and our capillary column is a 100m, .25 mm id column. Does anyone have an idea of what head pressure I should target? If not I was going to shoot for something higher than expected but being that I know little about GCs I was concerned that too much pressure may damage the column. I thought I would ask the experts first.

Thanks!

Hello,

Head pressure will determine the flow of carrier gas through the column. When looking for the optimum flow rate, linear velocity (cm/sec) is the measurement of choice. The optimum flow depends on your carrier gas. Nitrogen is around 10 cm/sec, He is around 30 cm/sec, and H2 is around 40 cm/sec. You can measure your linear velocity by injecting a non- retained compound like butane. The velocity is the length of your column in cm divided by the time it takes to see the butane peak in sec. You can then adjust the head pressure to get the desired velocity. If your carrier is H2 or He, I would start with a head pressure of around 40 psig. If it's N, then 30 may get you in the ballpark.

Download Agilent's free flow calculator software.

. One person did write down 'pressure will be much higher when using with a new column'. That is all I have to go on.

That does not apply to capillary columns, so you can probably safely ignore a lot of what is in the notes !

Peter

He is is my carrier so I will start there and let you know if it doesn't work... thanks dlbenach!

Peter Apps - I think they are referring to 'old' columns in terms of outdated - ones that were originally used with the 5890. I would assume they had much larger IDs.
But I know exactly what you mean. Everyone who used to do GC work 15-20 years ago has tons of ideas how to get the machine to work. For the most part their memories aren't correct and the technology is different. I am glad I found this website. There is a fast response from people who know what they are doing.

I am trying to set up a 5890 gc.
...
We want to run for long chain FA and our capillary column is a 100m, .25 mm id column. Does anyone have an idea of what head pressure I should target? ...
Thanks!

I hope last post from the following thread may shed some light on your problem:

viewtopic.php?f=2&t=21064&start=0