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GC Troubleshooting—Carryover and Ghost Peaks


Troubleshooting in gas chromatography can be toughWe need to have the right peaks in the right places with the right shape every time, but what can we do when we have some extra peaks showing up? They are typically carryover from a previous run or ghost peaks from extra material being introduced in to the system. Eliminating cross-contamination, running long enough and hot enough, and keeping things clean will help us prevent these extra peaks from showing up. 

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Hi, folks! Welcome to another Restek Tip. Let's talk about carryover or ghost peaks today. Say we're doing some gas chromatography, and we have some extra peaks. If those extra peaks are especially broad, or even maybe like a hump in our chromatogram, there's a good chance that, that might be carryover. Material that's in our first run, but our run didn't last long enough for it to come out, so it starts to drag out and show up in subsequent chromatographic runs. How can we check for this? Probably the best technique is to do a no-injection instrument blank. We just run the instrument without making an injection, and if we see these really broad peaks show up, that's a very good indication that we have some carryover.

How do we fix it? Probably something along the lines of increasing our run time, or taking our run up to a higher temperature, or maybe even both of those. Say we have some extra peaks, but they're not particularly broad. They have nice peak shape. We'd usually call those ghost peaks. Because they're nice-looking peaks, we know they've chromatographed, right? That means they've been introduced into the system towards the front. Maybe in our injection, or contamination in the injection port, or perhaps even something like contamination hanging out in our syringe, a bad rinse file, or a dry rinse file, or even something with how we've prepared our sample. That's where we want to focus our troubleshooting attention for a ghost peak problem.

And if you're having an awful lot of trouble with it, just change your paradigm a little bit. Call them bonus peaks and move on with your day. Thanks very much for joining us for this Restek Tip.