Chromatography Forum

Hello,
I'm try to figure something out. I'm using an Agilent 7890 CG and have recently started to use a guard column. Our software (Atlas) asks for the the column length. Do I need to add in the length of the guard column (5 meters) to the analytical column (30 meters)? This is what I'm currently doing.

Any insight would be appreciated.

The instrument calculates column flow from the head pressure and column length. If you add 5m of 0.25 guard column to a 30m 0.25 analytical column you have effectively made a 35m 0.25 diameter column and the instrument software needs to know that to calculate and set the column head pressure to achieve the flow rate you want.

If you add 5m of 0.53 guard column to 30m of 0.25 analytical column, then it would not matter as much since the restriction of the 0.53 guard would only be equal to a few cm of additional column.

Thank you very much.

Does the software calculate length if you time an un retained compound?

If you are talking about dead time I don't believe so.

I don't recognize the Atlas software, but MSDChemstation has a column calibration section in the software where you can enter the retention time of a non retained peak and it will calculate the column length.