I am new with ion exchange HPLC columns. I am following an EPA method for DiThioCarbamates (Metham sodium) which uses a Supelcosil LC-SAX1 column (25cm x 4.6mm x 5um) and has a 45% MeOH to 55% water pH buffered to 6.9. There also is a component in the buffered water of HexaDecylTriMethyl Ammonium Bromide. Embarrassed to say that I don't know what this does.

This first injection looked like it had a problem - but I thought could be worked with and might work. The chromatogram looked like 2 peaks where the first was twice the size of the second which melded into a shoulder where they weren't resolved really at all.Image
The subsequent injections - even after running a MeOH and a the 6.9 buffer water eluent rinse injections looked even worse.Image

Can anyone explain what I am seeing? BTW, the Metham Sodium target analyte is stable at a pH of 6.9 but unstable below that breaking down to Methyl IsoThio Cyanate (MITC). Since the Metham is stable above 6.9 pH I should get one solitary peak not two, and certainly not some ski slope tail after the first peak comes out.

Thanks in advance!