Chromatography Forum

I have a basic compound, without amine additive like triethylamine the peak is very broad, with 0.5% TEA the peak is much better, but still there is prolonged tailing(over 1 minute) which yields 5% impurity into next peak.
i believe 0.5% TEA is strong enough, how can I sharp it more so it won't extend it over a minute and into next peak.
i need to use all-subsituted amines like TEA but not diethylamine or amomium hydroxide for reactivity reasons.

Did you try various pH, and/or different columns?

DId you try more % of organic solvent to make your peak to get out before?

Before and at addecuate pH. Stady this.

Regargs

sorry, here are more info:

this is a preparative job, so normal phase is prefered. no pH option is avalable.
only this column with TEA shows separation, no other columns working.
more organics will push closer of the 2nd peak than sharpening the tailing so it will get worse.
thanks,

Why is there this preference of NP and why the pH restriction?

it's large amount to purify, my customer doesnot like getting tons of water to dry it afterwards.

give HILIC a try, use bare silica column, or similar

high organic mobile phase, should have separation

i had no success in scaling up with HILIC. limited success on analytical as well.
beside, the buffer salt in HILIC is not compatible for reactivity reason.
definitely neeed guidance on the scale up if any one has successfully done it?

Does the tailing occur at all loadings or only under your prep conditions? If it's a high-load phenomenon, your options are to decrease the load and do multiple injections or keep the load high, split into smaller fractions and re-process the lower purity fractions.

You didn't give details on your stationary phase and whether or not there is any water in your mobile phase. If the stationary phase is silica, you can often reduce tailing by adding polar modifiers (e.g., water or MeOH) at low levels instead of (or in addition to) the TEA. If you're using a bonded-phase material, this is less likely to help.

the tailing happens even at analytical level.
right now i just do the same thing you mentioned, reprocess the lower purity fraction. but it decreases the recovery and prolong the process time. i am not happy about the latter, and customer not happy about the first.

Hello!!

What is your analite? i'm thinking in other organic buffers like used to analize proteins . I've never worked on it but is a sugestion..

Regards

You've pretty much covered the "usual suspects", so at this point it's likely to be a major project to improve things.

1. Try even more TEA (on the grounds that "if some is good, more is better").

2. If you're using silica, take a close look at things like pore size (versus the size of your analytes) and purity (residual heavy metals?).

3. If you're using a 100% organic mobile phase, try adding trace water or MeOH (that's a stab in the dark, because the TEA should be suppressing any active sites, but I'm out of other ideas).

Let's review your HILIC attempts.

it is mentioned that you had no success in scaling up with HILIC, and limited success on analytical as well and trouble with salt incompatibility.

Did you ever try to leave out salt? It is not a necessity to use salts in HILIC, however many compounds get high retention due to electrostatic interactions if the pH is infavourable, i.e below pH 5 for bare silica columns etc.

In what way did you not succeed in the up-scaling.
I have long experience in scale-up and method development using HILIC, and can try my best in helping you out if you give somewhat more details....

Again, what about pH variation (maybe it should be called acidity variation here)? Adding acetic acid instead of TEA?

to Mueller,
the TFA is not working, but you and Tom reminds me that I may try to add TFA to TEA, see how it works. usually this is the last thing i would do.
the metal content is not a problem, checked with the vendor. the pore size is 120A, but this is what the matching prep column is, so i am going to see how much improvement on analytical scale first.

to HILIC ideas:

i have never get it worked on scaling up(resolution totally lost) my feeling the resolution in HILIC is very fragile; and no buffer salt, no separation either.