Chromatography Forum

I'm about to undertake some work on an alkyl guanidine derivative R-NH(C=NH)NH2 (where R < 8 carbons) and have not had success in picking up some initial method ideas from literature. It seems the functionality of these compounds would make them amenable to a number of method variations such as anionic pairing and cation exchange, but am curious if users of the board would suggest a different starting point. It's likely the compounds will have both organic and aqueous solubility, so perhaps HILIC comes into the equation too?

All insights with respect to mode and useful column types are welcome.

As an additional question, are there any particular pros and cons when dealing with alkylsulfate / alkylsulfonate ion pair reagents, if I end up going that route? In our lab the sulfonates seem to be preferred (simply looking at the shelves ) but I can't find anyone there to give me a basis behind it.

thanks

JA,

I have a perfect staring point for you; check the following method for guanidine. Your alkyl derivatives will retain based on two mechanisms: reverse phase and ion exchange. You can use TFA, ammonium formate, ammonium acetate, formic acid, phosphate buffers (depending on your detection technique):

http://allsep.com/makeCmp.php?cmp=Cmp_049

Thanks SIELC, good point about the detection technique. I think these cpds have a weaker chromaphore than guanidine; what ELS and conditions did you use there?

Dear JA,

We are using Alltech ELSD, Model 800. Detector temperature is 60oC.
You can also use low UV in this application if you switch to sulfuric acid (0.1% of TFA is equal to 0.06% of sulfuric) or phosphoric acid in the mobile phase. For low UV (below 210) you can also use phosphate buffer.

In case of ELSD or LC/MS detection you can use ammonium formate or ammonium acetate 10-50 mmol (pH-3-6), formic acid (with a weaker Primesep column-Primesep C or Primesep 200 for example)., TFA, etc.

The key is to control ion-strength and organic content of your mobile phase.

Retention time of your alkyl guanidine can be adjusted by ACN (reverse phase mechanism) content and by nature and concentration of buffer (ion-exchange mechanism). I am suite that you can find suitable conditions for your separation. Contact us if you need more information.