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Peak tailing

Posted: Fri Jun 16, 2017 1:39 am
by cene
Hi all,

I would appreciate some advice on peak tailing I am noticing in some of my runs.

I ran a reference standard through our GC and the resolution on higher BP alkanes is not too good. Resolution is great up until around C12, and tailing starts to become an issue after that. See the image below. It shows C12, C14, C16, C18, C20.

http://imgur.com/a/Tdt9s

What could be the cause of this, and is this a significant issue? I have noticed no tailing in standard sample analyses, and these include compounds across the BP range higher and lower than these alkanes. I have not noticed tailing in the alkanes present in my samples, though there is usually a high background profile that may be disguising it.

Re: Peak tailing

Posted: Fri Jun 16, 2017 6:14 am
by tkubowicz
Hello

There are many possible sources of peak tailing.
I'd recommend:

1.Replace inlet liner (perhaps it has many active sites). You can also clean inlet
2.Cut first 10-20 cm of your column from inlet side
3.Make sure column is properly cut and has correct distance from ferrule tip (for Agilent S/SL is about 4-6 mm)

Good luck

Regards

Tomasz Kubowicz

Re: Peak tailing

Posted: Fri Jun 16, 2017 6:42 am
by Rndirk
I have noticed no tailing in standard sample analyses, and these include compounds across the BP range higher and lower than these alkanes. I have not noticed tailing in the alkanes present in my samples, though there is usually a high background profile that may be disguising it.


Could you elaborate?

So a solvent standard = tailing (like in your image)
Sample with same alkanes spiked or present = no tailing

?

If this is the situation, it is not uncommon in GC. Much more common however for stuff like pesticides compared to rather inert alkanes. It points towards activity in your system (can be anywhere like the poster above me said). Sample matrix (what kind of samples are you running?) protects your analytes from active sites in the column/inlet and give sharper peaks compared to solvent standards.

I would perform maintenance (see above). Visually check the old liner, inlet and column piece for septum particles, these are typical sources of tailing for high boilers. Also put a new septum above the inlet, and don't overtighten it.

and is this a significant issue


You're better off without it, but it doesn't make your data worthless. It makes the integration of peaks annoying, you'll have to pay attention to integrate the same peaks to the same extent troughout your calibration. The evaluation comes from your QCs of course.

Re: Peak tailing

Posted: Sun Jun 18, 2017 11:48 pm
by cene
Thank you both for the advice; next time I do some maintenance I will change out the liner and trim the column.

Re: Peak tailing

Posted: Fri Jun 23, 2017 2:25 am
by cene
An update on this.

I changed the liner out and tailing has improved, but I still see small tails on C16, C18 and C20. Inlet and liner are both clean. The sample is a CRM diluted in DCM, so there shouldn't be any activity associated with the sample matrix.

What should I focus on next? Trim the head of the column?

http://imgur.com/a/bcT3W

Re: Peak tailing

Posted: Fri Jun 23, 2017 7:39 am
by Rndirk
cene wrote:
An update on this.

I changed the liner out and tailing has improved, but I still see small tails on C16, C18 and C20. Inlet and liner are both clean. The sample is a CRM diluted in DCM, so there shouldn't be any activity associated with the sample matrix.

What should I focus on next? Trim the head of the column?

http://imgur.com/a/bcT3W


Yes. Did you change the septum? Did you see septum particles in your liner?

If you trim the column, it's a good idea to check the old piece of column under a light microscope to learn something. Do you see dirt or particles in there? Was the cut well made?

Re: Peak tailing

Posted: Mon Jun 26, 2017 4:00 am
by cene
Rndirk wrote:
cene wrote:
An update on this.

I changed the liner out and tailing has improved, but I still see small tails on C16, C18 and C20. Inlet and liner are both clean. The sample is a CRM diluted in DCM, so there shouldn't be any activity associated with the sample matrix.

What should I focus on next? Trim the head of the column?

http://imgur.com/a/bcT3W


Yes. Did you change the septum? Did you see septum particles in your liner?

If you trim the column, it's a good idea to check the old piece of column under a light microscope to learn something. Do you see dirt or particles in there? Was the cut well made?


Thanks for the advice.

The septum was already new; I changed it before I changed the liner.

The liner looked a little dirty, as was typical for a used liner, but no septum particles or other large particulates were present.

I will trim the column next time the instrument is down and see if things improve.

Re: Peak tailing

Posted: Mon Jun 26, 2017 7:06 am
by Peter Apps
What are your analytical conditions ?, flows, temperatures, column diameter and length ? Without that information everyone is just guessing what the problem light be.

Peter