'Shark Fin' Peak Shape

[Anthony Crawshaw]

Does anybody out there know the reason that we might see a shark fin peak shape?

This is different to normal tailing. The peak rises almost vertically as expected, but then rather than falling in a gaussian fashion, the peak looks more like a right angled triangle ie. the tail is almost straight from the apex to baseline.

Is this a result of column overloading (although we are about to reduce injection volume to check this out), or is it something like buffer concentration effects?

Any ideas?

Cheers
Anthony

[JGK]

The troubleshooting literature would suggest a partially blocked frit or void at the head of your column which is distorting the distribution of the sample at the column inlet.

[Noser222]

Shark Fins were discussed in this thread

http://www.sepsci.com/chromforum/viewto ... =shark+fin

It would help if you could post some details about your method...

[Anthony Crawshaw]

Unfortunately this is only seen for this particular compound. So I do not think we have blocked frits or poor column packing, where we would probably see it in everything we run.

[Anthony Crawshaw]

Thanks for the link Noser.

First off... Our shark is obviously swimming in the opposite direction as it is 'tailing' and not fronting as the example given in the link. The peak is also not an interfering peak but actually our main band.

We are also not trying to separate sugars, just a pharmaceutical compound..although with 16 known impurities not the easiest.

Column wise, we have tried several. Sunfire, XBridge Shield and Phenyl. All standard 150x4.6mm 3.5µm. We are seeing this on all the columns.

As for mobile phase, nothing exotic there, MeCN and 25mM Phosphate buffer.

The only other potential we may look at is that the sample diluent is actually MeOH and 25mM Phosphate buffer.

[Rob Burgess]

I presume this is for an impurities assay, where you would need to be in an overload situation to adequately see your impurities down to the required level. This is quite a common occurence (I have it with my current imps method) but there isn't much I can to for a work around as I need the sensitivity.

Either try drastically reducing you injection volume or diluting your sample. What is your sample type, concentration and injection volume?

[Bruce Hamilton]

I would start by dissolving your sample in the mobile phase, you may see that shape if the sample partially precipitates onto the column, especilly if fairly concentrated.

Solubility would be my first assessment, so try changing your initial gradient ( if using one ), reduce injection volume, or increase column temperature.

I assume your mobile phase pH is appropriate for the sample, and the sample doesn't contain a functionality that partially binds to the column ( which usually gives a longer tailing curve ).

Please keep having fun,

Bruce Hamilton

[Uwe Neue]

Without a chromatogram and actual data or a better description it is still tough to judge what is going on.

I understand that you have one huge sharkfin peak, while your other analytes do not show this.

Are the other analytes present in much lower concentrations? Are they not ionized, while the shark is ionized? What is the pH of your buffer?

[SIELC_Tech]

My guess is that if your compound is basic in nature you are overloading residual silanols. Try to dilute sample 10times and see if this helps.
Here is good study on overloading of silanols. Check article by McCalley "A study of retention and overloading of basic compounds with mixed-mode reversed-phase/cation-exchange columns in high performance liquid chromatography". Here is a link to the article:

http://www.sciencedirect.com/science?_o ... bb1575fdbf

[tom jupille]

Does it look something like this:



?

[Svante]

You say that you only see this for this particular compound. I've encountered a similar phnomenon with the peakshape you described. I separated the mono di and triphosphates of a nucleotide and was having a good peak shape on the monophosphate, the sharkfin you described on the diphosphate and the triphosphate was so badly distorted that you could not see it.

Anyway my problem was solved by adjusting the mobile phase pH and ion strength so maybe you can solve your problem the same way.

Good luck