Chromatography Forum

Dear members of this forum,

In several opportunities in different pharmacopeical techniques I saw that the working pH is 2.0 and the solumn is silica with C8 or C18.
In different references is mentioned that the down limit of working to this kind of column is 2.0. Always I adjust the pH in 2.5 but If I had decided to work in the recomended value of pH (means 2.0), I think I put in risk the column life and more when the columns which I work not allowed to work with pH below to 2.
I would like to know why the United States Pharmacopeia adjust the aqueous part of the mobile phase to 2.0 and recomended a general column C8 or C18.
Thanks in advance for your advices,

Diego Delmonte

Dear Tequila (rested?, or aged?)

All columns, no matter how careful you are, will die some day. The truth is that silica columns will have a shorter life at lower pH values. The more you approach pH 2, the shorter the column life. USP and other compendial books, list pH adjustments in methods that were developed years and years ago, perhaps when these aspects of column stabilities where not well understood. Or perhaps the pH variations in the method were not studied and the author just simply adjusted to pH 2 without any more thought. The chemical deterioration at low pH values is a loss of stationary phase by hydrolysis.

It is also well accepted that all methods can be "adjusted" in some of their operation conditions without seriously changing the method. In the case of pH I believe the change is + - 0.5 units. Therefore you are doing well adjusting to 2.5 instead of 2.0

Good luck,

josebenjamin