Chromatography Forum

Hi folks,

Got a question. Hope some one can help.

We were trying to separate BHT and BHA (Butylated Hydroxyl Toluene and BH-Anisole) on a C18 column using 50/50 Water/ACN (I think). Anyway, we found that BHA was very sensitive to slight mobile phase change. Adding a little bit more water and the BHA peak shifts way off the chromatogram. BHT was okie though.

Just wondering what causes this......I thought it might be a column equilibrium issue or are there some thermodynamic explanation for this behavior?

Thank you all.

Add some acid (acetic acid or phosphoric acid, or an acidic buffer) to your mobile phase. Both have phenolic groups, but the one on BHT is so sterically hindered that it doesn't behave as one, and I'd bet that the BHA needs acid to force it as the phenolic form instead of ionized.

AOAC 983.15 is a standard method for BHA and related anti-oxidants. They use water/MeCN/MeOH/acetic acid. I have done it and it is pretty stable.

Thank you Consumer Products Guy and Mark.....much appreciated.