HPLC ion exchange chromatogram nasty

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

2 posts Page 1 of 1
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!
Hi LabPro,

More detail regarding the method would be helpful, such as retention time(s), flow rate, and maybe an attached chromatogram.

I couldn't find the method online to read for myself. The easy part is the HexaDecylTriMethyl Ammonium Bromide (a.k.a. cetrimonium bromide), this compound is a cationic surfactant which ought to form a nice ion-pair with the methyl dithiocarbamate ion (anion). This ion-pair should increase the retention of your analyte--if you were running a reverse phase separation. I'd think that the SAX phase wouldn't require the use of the cetrimonium bromide at all...method details would be helpful here, too.

Guess this will do for a start...
MattM
2 posts Page 1 of 1

Who is online

In total there are 12 users online :: 0 registered, 0 hidden and 12 guests (based on users active over the past 5 minutes)
Most users ever online was 234 on Tue Feb 06, 2018 7:33 am

Users browsing this forum: No registered users and 12 guests