Need to separate two amidines in the mixture of amide and three diamines - no UV activity on three of the compounds. Your help is appreciated.

Although I can't help you with the amide, diamines are readily separated on a Dionex IonPac CS17 column. I don't believe we have looked at amidines on this column but I'm pretty sure they should work as well on this column. In this case, detection is accomplished using suppressed conductivity detection so no UV activity is required. If you're interested in more information you can e-mail me directly or visit the Dionex web site. If interested, I could have someone here take a look at your compounds on this column.

HILIC on a silica column could be a good tool as well for the separation of these compounds. With amides and amines, you might still do OK in the low UV, if you do not use methanol in the mobile phase. Refractometers are an alternative, but they are not very sensitive and it takes half a century until the baseline is stable - not very pleasant for method development. One of the modern detectors such as ELSD might do fine for you, if the MW of your sample is high enough.

In situation you’ve described nothing works better than mixed-mode columns. If compounds are drastically different in hydrophobicity and pKa value you need at least two types of interaction to create a method where all components are resolved in reasonable time with good peak shape. See an example of the chromatogram of separation of guanidine from sodium (http://allsep.com/makeChr.php?chr=Chr_019). Guanidine in many aspects of chromatography behavior similar to amidines on Primesep columns. In addition this is reverse phase column that will separate all compounds based on their hydrophobicity. MeCN/H2O/H3PO4 should be used to get low UV transparent mobile phase down to 195 nm. At this wavelength all amidines and amides are visible. Amines can be detected too if they have a carbonyl group somewhere in the structure. If you have access to ELSD the phosphoric acid should be substituted with TFA in 2:1 ratio. Adjust amount of MeCN to retain most neutral and hydrophobic compound in convenient for you time frame. Contact Allsep Technologies for aditional information.

I donnow Selechonok ... the problem is not the retention of the amines, the problem is the simultaneous retention of the amines and the amides. You first worry about getting the amides retained, then you worry about elimitating ALL the effects that will create special retention of the amines. I know that you want to peddle your new stuff, but it would help if we all think first before giving bad advice. Your stuff is designed to create special retention for ionic compounds, not eliminating it.

To Anonymous above:
Would you please specify "about eliminating ALL effects that will create special retention of the amines". I visited Allsep website but did not see any special approaches in terms of mobile phase. What do you mean? because they are using ACN-water-TFA, and at this condition non ionic compounds are retained too (somewhere on their site there is complex mixture with different compounds). I don't know how accurate is the statement of this Zelechonok guy, but I do not see (in theory) the problem with the retention of amides on mixed modes columns (or any reverse phase column with low organic in mobile phase)

For ionic compounds, we typically play with pH to change the ionization. In this way, you can change the retention of bases or acids often by a factor of 30. This allows you to bring the amines and the amides into the same retention window. We have plenty of applications with XTerra columns that use this principle. Detection maybe ELSD, as A.Mouse suggested.
As an alternative, you could try derivatization (if your compounds allow it, of course).

Why anybody needs to [worry about 'elimitating' ALL the effects that will create special retention of the amines]? If you, anonymous with special retention, know all the solutions why don’t you give an advice… What so bad about my suggestion? I see nothing wrong to give a simple solution and promote a new product, do you?