Trouble Deciding Which Inlet Liners To Use

[Cody]

My lab currently does EPA methods 504.1, 508.1, 515.4 and 552.3 for drinking water analysis. We only have one instrument (Agilent 6890N) and currently use Restek Pesticides columns to run all four methods on the same instrument. Does anyone have any suggestions for specific inlet liners to use for best results and separation in this situation? I do not have much experience when it comes to GC analysis (I had to jump right in just a year ago when the chemist above me suddenly retired). Was hoping that someone on here who has had plenty of experience with these methods would have some suggestions.

[aidnai]

What liners are you currently using, and why are you wanting to change (i.e. what issues are you having with the chromatography)?

[Cody]

Currently using Restek Sky 4.0mm ID Double Taper Inlet Liner. Restek has suggestions on instrument parameters and liners to use. Three of the four methods I stated have suggestions of liners that have a intermediate polarity (IP) deactivation. When I started these methods almost a year ago, I had amazing success with 515.4. However, some time after that, I replaced the liner with some new liners that my supervisor ordered just for preventive maintenance. I had been running the instrument a lot compared to its usual usage by doing my MDL's, LFB's, etc. (usual start up QC samples for instrument competency). Well, the problem is that I can't remember if the liners I replaced where the same ones as the liners I replaced them with. I know that the liners I currently am using are "Sky Technology" deactivation (and I don't know what that entails). I haven't been able to have much success at all with my 515.4 or 508.1 since around the time that I first changed my liners. Also, I honestly don't know if my supervisor ordered me the correct liners at that specific time. So it could be a possibility that I'm using the wrong liners due to his mistake.

My chromatograms are different (slightly different retention times but drastic difference in analyte response; much lower response now). This makes it hard to effectively quantitate. I'm also having issues with peak tailing and poor resolution of peaks in general (some I wouldn't even call peaks anymore but just humps). I've been trying to fight these issues for almost 6 months now and it just came to mind about the inlets so I figured I would ask. Again, working with the GC is still a very new experience for me and I'm constantly learning things about the instrument. Would those who do pesticide/herbicide analysis by 515.4 or 508.1 suggest using a specific inlet liner?

[aidnai]

Would you be able to post any chromatograms before/after? It would really help us quantify what you mean by "amazing success with 515.4" vs. now with lower response, tailing, poor resolution, etc.

[Cody]

I'm just looking for what everyone else uses or suggests for those specific methods. By "amazing success", I meant I was able to get all acceptable curves according to the EPA methods (R^2 values of 0.995 or higher), also acceptable LFB's and MDL's all on my first try. I was also able to pass PE testing during that time.

Those results are "amazing" compared to what I'm getting now, which is completely opposite. Again, I'm just asking for what people use for these methods.

[Yama001]

A double taper liner is a pretty good choice to start with, Restek Sky is more a marketing scheme than anything else. We have not seen them to be better than any other suppliers deactivated liner (I think we use Restek's Siltek line now, we have used Agilent, Supelco, Phenomonex).

We use a single taper liner only because they may be cleaned and reused after a suitable silanization.

A good liner is important, but real world samples mess things up, so inlet cleaning (including the split line) and column trimming or replacement can not be neglected.

[Bigbear]

For those methods we use Agilent double taper liners. The Restek ones should be fine.

Are you sure your issues are liner related?
How often do you do other maintenance? Change seals, clip (or replace retention gap), clip the column head(s)?
In our experience it seems as the 552 extracts mess up other methods chromatography over time. Doing the above maintenance restores the chromatography. We do 515 and 551 on one instrument.

[mckrause]

Running those 4 methods on the same GC, liner and column would be a difficult task for an experienced chromatographer, much less someone with limited experience.

While you definitely need to routinely change liners, BigBear is correct (and being very gentle). You need to trim the column, change the liner, check the septa and in general make sure the whole system is functioning at it's peak; these are not simple chromatographic methods and a whole lot of bad things can happen.

In our experience it is very difficult to run the HAAs on the same system as the derivatized herbicides.