GC Inlet Liner Troubleshooting: When the problem isn’t your liner25 Feb 2011
I get a lot of ribbing from my colleagues because for the past two years I’ve spent a lot of time thinking about GC inlet liners. I’m cool with that, and it isn’t because of my unshakable self-esteem (actually, I’m quite sensitive, thank you very much). It’s because I feel that my colleagues and customers sometimes struggle with liner-related issues, and I like being a resource for them. How good a resource I end up being I invite you to discover for yourself (but remember the sensitivity thing).
So, that being said, you’d think I’d being talking about all the problems your liners really do contribute to your analysis (and believe me, there is plenty to talk about here). However, a recent experience in the lab drove home the point that chromatography is hard. What’s that you say? A piece of cake?!* No, no! I contend that it is hard! And what doesn’t make it any easier is the fact that certain symptoms that you observe chromatographically can be caused by a number of different and sometimes totally unrelated sources. So, how do you troubleshoot in a way that isn’t spastic? Well, like good science in general, I think one key element is making good observations.
Okay, on with my story. I sat down to use an instrument to collect some data on (drum roll) liners. I started by removing the liner that was already in there, and I noted that the liner had some septum particles in it. Bad news, right?
However, I proceeded to replace the inlet consumables (septum, liner, gold seal – it was an Agilent 6890) and collect my data. I was looking at endrin and DDT breakdown results, and I observed something that I thought was odd. The first analysis exhibited extremely low breakdown values for both endrin and DDT. The second analysis showed an increase in breakdown by over an order of magnitude for endrin alone? That blasted liner!
Or was it? When I removed the liner I noted it had a smallish chunk of septum in it. That blasted septum!
Well, hold on. I thought to check out my syringe, and I noted that it was in fact a 23 gauge needle (still cone type tip), not the recommended tapered 23-26s gauge needle. Ah ha! Blasted syringe!
Or, perhaps more appropriately, blasted Scott (sensitivity meter rising).
Why do I mention this semi-embarrassing tale? I do it to illustrate how the choice of syringe created a problem that could have easily been attributed to the liner or the septum. We’ve observed that things like vial caps, detector installation distances, FID collector installation, etc. can also give these kinds of confusing results.
If it helps, I’m happy for you to learn from my silly mistakes, because for your analysis they may not end up being that silly.