I'm trying to determine a better mobile phase for separation of reaction products on a Waters Symmetry C18 column. I realized I don't know what are commonly accepted as C18-compatible mobile phases. I've used water, dilute aqueous buffers, methanol, acetonitrile, and isopropanol in the past. Are there other solvents that you consider standard C18 mobile phases? Are there any (other than high and low pH aqueous solutions) that you consider absolutely incompatible with reverse-phase HPLC? Your thoughts would be useful.

Thanks,

THF

They are the most commonly used. Basically you can do many things with water (buffered)- methanol and acetonitrile... The only thing you didn't mention is that with you aqueous phase you can add ion-pair reagent for some analisys.

Depending on how is your C18 column (if there is any other component besides silica) you cannot use Dimethylsulfoxide.

And to get acid or basic phases, there are some reagents that can be very agressive, like perchloric acid. For this purpose, the most used are phosphoric acid, acetic acid, diluted NaOH, KOH. There are many others but you can work well with those ones.

Renata

For the Waters Symmetry C18 column, the useful pH range is 2 to 8. It is compatible with most solvents that I can think of, with the possible exception of amines. You are more limited with your detection than with the column compatibility. Standard solvents are water and buffers in the pH range mentioned, methanol, acetonitrile and THF. If you work with MS detection, you could think of acetone as an interesting solvent, but it is not suitable for UV. Most people do not use DMSO or DMF, since the visocosity of mixtures with water is fairly high. This is the reason also why people usually shy away from IPA. From a selectivity standpoint, methanol is fine.

Hi Renata

Could you expand your statement of "Depending on how is your C18 column (if there is any other component besides silica) you cannot use Dimethylsulfoxide"


Do you mean that DMSO should not be used on non-silica columns (like Xterra)? Or are you saying that you shouldn't use DMSO with a C18-silica column? Does some reaction occur?

I see that DMSO is a strong solvent and therefore could cause retention shifts and peak shape deformity. I am more interested in the prospect that DMSO would destroy a column.

DMSO is not reactive or destructive to columns, neither to a silica column nor to an XTerra column. The only problem with it is that it creates distortion of peaks, if the injection volume is not kept rather small. This has nothing to do with the column, it is just the DMSO.

Most packings can be used from pH 2 to pH 8. There are a few packings that can be used in the more acidic range: the standard example is the line of Zorbax columns with the bulky side chains, but other packings with di- and trifunctionally bonded ligands can be used in the pH range below 2 as well. For the basic pH range, the most known examples are the XTerra packings and the Zorbax packing with the bidentate ligand. However, other modern packings are supposed to be useful to pH 9 or 10 as well. The stability of these packings (e.g. Luna (2))probably depends on the ligand density, which is higher for modern packings.

Hi Anonymous


I was referring to columns based on porous monolithic rods of silica, as Chromolith (Merck)

Renata