Increasing internal standard peak area

Chromatography Forum: GC Archives: Increasing internal standard peak area
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Baffled on Sunday, April 6, 2003 - 07:49 pm:

I was wondering if anybody could shed a little light on this...

I prepared a number of stock butyric acid solutions of varing concentrations on a base of heptanoic acid internal standard. I noticed as i ran the acid solutions that the size of the internal standard peak was increasing for increasing test acid concentration. I assume that this should not occur as the internal standard was the same for all prepared samples.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Sunday, April 6, 2003 - 09:12 pm:

Hi Baffled,
You could be experiencing some sample carry-over. You may have remnants of previous samples in the inlet or column. Try increasing the final temp and lengthen the run time to allow for the complete elution of the previous samples. If this doesn't help, you may want to clean your inlet. You can also condition the column at a temp higher than has been used but lower than the maximum contionuous operating temp for the column. Cut 4" of the inlet end off before reconditioning it. You may also want to try a different temperature program and/or different type of liner.
Hope this helps.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, April 7, 2003 - 08:30 am:

You can verify sample carryover via a contaminated inlet or column by performing a 'blank' run immediately following a sample. You shouldn't see any peaks if your system is clean. I would try this before dismantling your instrument to clean the inlet.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Mark Owens on Tuesday, April 8, 2003 - 07:30 am:

Dear Baffled,
Another possibility might be that the column is getting "conditioned" during the injections, that the acids are being held up by the column. I know this was a major problem with the older packed columns and that the newer cap columns are not supposed to do this but I have seen it happed before. Would it be possible to add a small amount of formic acid to the preps and see if the additional acid will even out the responses? Formic should not interfere, it will elute very early and on a flame detector have minimal response.

Hope this helps,
Regards,
Mark


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Rodney George on Tuesday, April 8, 2003 - 12:38 pm:

Good answer, Mark.

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5702 fax
rgeorge@sial.com


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