Two Peaks for a Single Compound (13-C)

[GGRUW]

Hello,
I am analyzing two surfactants (both acids) using HPLC on a Poroshell 3x50 mm 2.7um column and am finding that there is consistently double-peaking at two retention times for the 13-C internal standard for one of the compound (0.4 minutes apart). The compound itself it usually ok, but does sometimes have a smaller double peak. When I analyze the standards on a larger 4.1x150 mm, 5um column, I do not see the split peaks. Any help is greatly appreciated!!
Image here: http://imgur.com/yEoFCOc
Method Flow rate: 0.8 mL/min
Injection Volume: 2 uL
Gradient: A2= 2 mM AmAc in water; B2= 2 mM AmAc in methanol
0 to 0.25 min 40% B2
0.25 to 2.50 40 to 100% B2
2.50 to 7.00 100% B2
7.00 to 10 min 100 to 40% B2

[tkubowicz]

Hello

Please paste chromatograms and write method parameters.
Otherwise it will take ages to guess what kind of problem you have.

Regards

Tomasz Kubowicz

[bunnahabhain]

What is the pKa of your analyte? Maybe the two peaks are charged and non-charged species of the same compound. Try to run this method with 0.2 % formic acid instead of AmAc and see what happens. And reduce dwell time for your copmounds, you only have 5 points per peak, this is not enough for reliable integration.

Edit: I just saw your daughter ion is 80 m/z: Is your compound a sulfonic acid? If yes, formic acid will be too weak. Better try a mixed mode column, see sielc.com if you find similar compounds in the applications list.