Chromatography Forum

I am using a LunaNH2 column for separation of some very polar analytes after recommendation of the supplier, Phenomenex. Although I am getting reasonable separation, I'm finding that the peak shape (fronting) is getting worse within a few weeks of use. I can improve the fronting by lowering the sample concentration, but I am concerned about the rapid change in performance of the column.

Please let me know if you have much experience with the lifetime and inter-column robustness of LunaNH2 columns and how it compares with other NH2 columns such as Hypersil-APS-2.

Talk to Phenomenex, point out your concerns, and nicely ask how they plan to resolve the situation.

They should react in some positive way. If not, consider other suppliers ( eg Agilent, Waters ), noting that some amino columns are more fragile than others, and good columns probably cost a little more.

Please keep having fun,

Bruce Hamilton

Give them a call, let them know what the problem is, and substantiate your position with data. Let them know about the sample matrix, what you do to prepare the samples, mobile phase composition, prep,and so forth I've always found Phenomenex' customer service to be excellent.

I agree with juddc. This problem is most likely due to sample prep. I would look at the following:

a). sample cleanup procedure

b). sample diluent composition - should be similar to mobile phase
(but not always possible)

c). sample diluent buffer / ionic strength, ect. My guess is peak shape could be improved if you are able to increase the buffer capacity of either the mobile phase or sample diluent (or both). This would be consistent with the observation of injecting less solute and seeing improved peak shape.

I would also like to say that if you are unhappy with the particular of NH2 phase you are using, you can shop around. Ask the vendors to show you durability / reproduciblity data. I would argue that it's very easy to differentiate between good and bad NH2 phases (based on data).

We can provide such durability / reproducibility data for our NH2 phase. If you're interested, let me know and I can forward it on to you.

Are you running aldehyde or ketones in your matrix. If so, NH2 is a definite no-no.

Can you elaborate on the conditions of your run. Tailing and fronting can be pretty bad on a NH2 column - unless the right conditions are chosen.

If a chance exists, I will shift to a CN or OH column instead of NH2.

Though it may not be the cause of your problem, amino columns can accumlate "junk" from the mobile phase. You can reduce this by putting an amino phase filter between the pump and autosampler. The Phenomenex column guide has a cleaning procedure that you can try, if you haven't already.