Chromatography Forum

Hi all,

I am working on adding EPA 515.3/4 to our lab and I am looking for any tips to improve resolution and tailing. We are running a 6890N/micro-ECD (instrument also runs 504, 505 and 552 regularly.) I've shot several standards at 5-50 ppb using a few different sets of conditions, working off those recommended in the method and by Restek. Resolution and peak shape have not been satisfactory, especially on the secondary column. (Standard is the Restek methylated chlorinated acid 16-compound mix with methylated surrogate.) Thanks in advance.

Current best conditions:
Agilent J&W DB-1701 primary column, DB-5.625 secondary
He carrier gas, constant pressure @ 15.4 psi
2 uL injection vol, double gooseneck Sky liner @ 225 C
Detector temp 290 C
Temp program:
70 C hold 1 min
20 C/min to 150 C, no hold
10 C/min to 280 C, hold 5 min

My first take is that you are injecting too much. Are your columns 0.32 dia? We run 552 and 515 on the same instrument, and inject 0.2 ul split less.
First try lowering your injection volume.

0.25 mm / 0.25 thickness. I'd prefer to run 0.32 with a better stationary phase but that would require revalidating the three methods we currently run, which has been a hard sell to the lab manager so far.

We're not currently set up to inject volumes that small, and I'd worry that trying to hit some of the state reporting limits (under 1 ug/L) would be difficult with such a low volume. I'll give 1uL a shot and see if there's any improvement. Thanks.

How long is your splitless injection? I'm at 0.4 min currently

On a good day I can see 0.5 ppb for all my compounds except PCP which I calibrate to 0.1 ppb.
If you use an Agilent tower injector using a 5ul syringe, and the nano liter setting on the gc, you can inject 0.2ul.
How are you splitting into the columns? I use a Restek MXT Y connector.