About Mobile Phase with Triethylamine

[Tequila]

Dear members of this list,

I am analyzing certain analyte which amine group with one C18 no endcapped (Lichrospher RP18). The mobile phase is Buffer Acetate with TEA - Methanol - Acetonitrile (25:35:40), the concentration of TEA in the Buffer is 0.3 % (v-v). The peaks have tailing which I would like to eliminate. My next step is increasing the concentration of TEA but in all the information I have looked the concentration of TEA is not more than 20 mM. I would like to know with you until until what concentration of TEA I could have in the buffer acetate. I think other possibility, the decreasation of pH with other buffer as phosphate but the limit of ph to my column is 2.5.
I would appreciate any help,

Diego Delmonte

[Victor]

Diego,

Lichrospher C18 is one of the older type silica-ODS phases. I would suggest changing your column to one of the newer phases e.g. from the same supplier as you are using (Merck - I think the Purospher-e range) or from Waters, Supelco (the Discovery range) or GL Sciences (the Inertsil range). You may be able to analyse your bases without using any TEA but with a phosphate buffer at pH 3 or thereabouts.

[Steve]

I will mention that Macherey-Nagel column NUCLEODUR® has pH stability from 1 - 11. If you have time check this column out.

https://www.macherey-nagel.ch/web/MN-WE ... amesE?Open

[Benjamin]

Diego,

The analysis of basic compounds can be done using three basic strategies. The first one is to use a good column likely to give good peak shapes with strongly basic compounds, such as ACE 18, Zorbax SB-C8, etc. The second one is to use the lowest pH possible, something below pH 3 is usually enough, for this acetate buffer is not convenient and you will have to use phosphate. The third one is to try adding a small amount of TEA.

TEA itself is not very soluble in aqueous phases, and being a base it will increase the pH of your phase. You can add all the TEA you want but solubility and buffer capacity and pH limitations will put some restrictions on how much is recommendable.

I would recommend you try to double the amount of TEA you are using now, if you do not see any change in your chromatographic separation and peak shapes, then it would be unwise to add any more.

I hope this helps you. Good luck.

Benjamin

[WK]

Diego,
Have a look at the Quinine by HPLC-UV thread that I started in Nov04 - its on page 2 of Liquid Chromatography posts.
Victor kindly replied then and it sounds like a similar problem that you have.
I used the Discovery phase successfully but at pH7.5 not <3.0 - this was I think something to do with my plumbing system and nothing to do with the column - so try pH<3.0 using phosphate with one of the phases recommended above by other repliers.
Good Luck
WK

[dlorenzo]

Diego: are you from uruguay?