My problem:
I tried to separate on RP-HPLC (C18)a fairly basic compound (eluent: methanole-water and 0.1% trifluoroacetic acid). The result: peak tailing and very broad peaks.
So I changed the mobile phase by adding 0.01% triethylamine, but the peak shape stayed the same, only a decrease of the retention time could be observed.
I don't have much experiences, therefore I really need your help...

You could try using a buffer instead of water in the mobile phase--that might stabilize the compound a little better than plain water/TEA. Just make sure the pK of your compound is ±2 pH units from the pH of the buffer.

You might want to go to one of the polar-linked columns (Symmerty Shield, Bonus RP, etc).

What type of column are you using. A well base-deactivated, endcapped column should imporve peak shape if you are currently using an older ODS type packing.

My problem
I tried to separation by RP-HPLC(C18)a amphoteric compound in dye cosmetics (ex; 4- Ethoxy -m-phenylenediamine sulfate, touene -2,5-diamine sulfate...)
My eluent had 95% water with
0.5M 1-pentanesulfonic acid.
The result: peak tailing and broad peaks.
I don't know the reason.
If you know the reason tell me about it.

I'm checking files about the analysis of waxes.
(jojoba ester, bees wax, montan wax, etc. :
Cosmetic raw materials).
But, I can't find them.
If someone know where they are, please tell me
about them.

I have worked with some pharmaceuticals which had big tailing in usual C18 columns with methanol or acetonitrile:water mobile phases. ALmost every problem was reduced changing water by phosphate buffer (10 to 25 mM) prepared from phosphoric acid adjusted to the desired pH with triethylamine, and working with a SymmetryShield RP8 25 cm 5 um column.
I have tried also with Discovery RP-Amide column, but results are not as satisfactory and selectivity was totally different.

I've been working succefully with Luna C18(2) columns (Phenomenex)with buffer KH2PO4 pH= 3 to 7 without using any amine (TEA, DEA)to improve peak tailing (T< 1.5, USP) for basic compounds like pseudoephedrine, chlorfeniramine, diltiazem, cathecolamines, substituted pyridines, etc. Another column could be a Merck Purospher. But if you still want to use old silica columns, a better amine to improve peak tailing will be dimethyloctylamine (DMOA)(0.05 - 0.2) together with a buffer 20 -40 mM KH2PO4.
Good luck!

I would like to ask also about Luna C18(2) column (Phenomenex). This column is so hydrophopic, that when I analyse some weak acids (pKa about 2-3, e.g. 3,5-dinitrobenzoic acid), they are retarded strongly even without any modifying acid added.
Surprisingly, diminishing pH (by adding HCOOH for example) is diminishing the retention factor!!! Usually it should be in opposite way. At lower pH the analytes should be less ionized and more retarded on the column.
Can you tell me what makes this column so exeptional?