Chromatography Forum

I am running a 6890 Agilent GC with splitless flow. I recently dropped my run time to 14.25 minutes for pesticides and the chromatography looked great. However, suddenly, I began getting what appear to be double peaks for the same analyte: a large normal peak and a small hump attached following the initial peak. I can only assume this second small shoulder is part of the initial "parent" analyte, since it is occurring for each peak in the first half of the run. I switched back to my normal run of 24 minutes to see if there were any change--there was not. Has anyone experienced this, or are there any suggestions in correcting the problem. It is making integration and calibration impossible--I cannot rely on what may be part of the same analyte. Thanks in advance for any advice!

What is your old and new oven temperature pgrm?
What is your solvent and column?

Which pesticide and have you purchased new standards recently?

This secondary peak could simply be a different isomer of the pesticide.

Hi
I'm sorry about my (very) bad english
If appears doublepic in many pics of your cromatogram it's possible a problem with the injection.

probably the column was dead or overloading. Check with new column and smaller injection volume.

try lower initial temp of column: the problem is simply injection problem
good luck

I have seen this with a Thermo Focus GC and AS 3000 autosampler. Simply increasing the injection needle dwell time to 2 seconds solved my problem. Never noticed anything like that with the Agilent autosampler which seems to have the fastest injection i know of.

Hello!
test see if the gold Plated is clean?

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