Retention Time Shift

[Muhammad Akbar Khan]

Hi everyone,

Here I am using Agiletn 7890A system GC, here problem is retention time of FIDA has been shifted from 3 min to 8 min of C1. I checked the leakage everywhere and also check the oven program, I did not find anything wrong with temp and leakage, So how can I reduce the retention time of FIDA.

Thanks and Regards

[dblux_]

Hi everyone,

Here I am using Agiletn 7890A system GC, here problem is retention time of FIDA has been shifted from 3 min to 8 min of C1. I checked the leakage everywhere and also check the oven program, I did not find anything wrong with temp and leakage, So how can I reduce the retention time of FIDA.

Thanks and Regards

Are you sure nobody changed your column for much longer (or even changed carrier gas) ?

Jokes aside. You "checked for leaks and oven program", check column flow as well.

I wonder what you mean by FIDA. If it is FID on channel A than you can't reduce retention time of "FIDA" (detectors don't have retention times).

[chromatographer1]

If you suddenly cracked a column to FID A that would explain the increase in retention time.

I assume you have a column on B. If not, then you might be running out of carrier gas, or someone changed the pressure on the regulator on the tank or on the GC itself.

AS previous posted, check the FLOW through the column.

You could also have a partially blocked flame tip.

best wishes,

Rod

[dblux_]

Muhammad, I hope you haven't played with EPC calibration since this affects flows directly.

Before you solve your serious problem (doesn't mean hard to solve) you can't use your instrument even for quality analyses.

[Don_Hilton]

What was your instrument configuration before and again after the change in retention time? Have you added a Y connector in the oven or changed columns? Is your GC oven program the same - same oven temperture profile and same column flow rate? Have you changed carrier gas - and have you by chance changed from using helium to nitrogen, which is less expensive - but requries some changes in instrument configuration.

And, While I've not seen it make a retention time shift quite this big (and was probably before the days of the EPC) -- what is the condition of your septum?

When you look down into the inlet - how does the bottom of the inlet look? free of crumbs and junk? How does the end of the column look. It is possible to overtighten the nut onthe front end - crush the column and obstruct the flow. But vefore chasing the question of obstructed flow, check the flow rate of the column.

[jdezeeuw]

If your C1 peak shifts from 3 to 8 min you have:

- a change in inlet pressure (could be a huge leak at connection, or septum)
- your column develops a restriction. (maybe liner or column is plugged)

If a PLOT column, this sometimes can happen if you use non-stabilized PLOt's.

Check the flows/pressures of your system.


jaap de Zeeuw, Restek Corporation