weak binding SAX/WAX column suggestions?

[lynzjm]

hi all,

we have used some Sphereclone 5u SAX and NH2 (WAX) columns for some of our studies and would like to know if anyone could help us with suggestions for any weaker binding SAX/WAX columns than these? Just meaning a different brand or type we could try if that makes sense! Suggestions welcome to see if they are any better than the ones we've been looking up!

cheers,
lynz

[Andy Alpert]

Sphereclone has a pore diameter of 80 Å. That means it will have a high surface area. Switching to an anion-exchange material with a wider pore diameter will decrease the surface area significantly. That alone will decrease retention. Good WAX materials with pore diameters of 300-, 1000- and 1500-Å are available.

Another approach: A WAX (weak anion-exchange) material loses charge density steadily as one goes from pH 5 to pH 9. Just running your application at pH 7 will afford shorter retention than at pH 3-5, unless your analyte has phosphate groups that acquire a second (-) charge above pH 6. I might note that this approach will not work with an SAX (strong anion-exchange) material, which characteristically keeps its charge density up to pH 9.5 or so.

[Vlad Orlovsky]

Hello Lynz,

We have different mixed-mode columns which have different pka values for both cation-exchange and anion-exchange columns:
http://www.sielc.com/Applications_By_Column.html

If you send me email with more information I will advice you on what to try. Also, I am conducting mixed-mode classes/seminars at the end of November in UK and you are welcome to attend.

[lynzjm]

thanks so much guys your help is really appreciated especially the pore size suggestions we'll look into that today. Our polymers usually have phosphates so we're being forced to work at lower pH's for that very reason which is the problem as we're getting them to stick to the column but they're not happy about coming off lol! We're getting there

I'll pass the link you sent to my colleague Vlad, she is comparing several manufacturers columns at the moment for us so we'll have a wee look! Its a complicated method as we're hoping to use it for several polymers, some with phosphate groups some without!

Many thanks,
Lynz x