Chromatography Forum

if bare silica column is very irreproducible, why people use it for prep scale preparation.

It's cheap.

but how can we deal with its irreproducilbility?
we just use it for one time run?
or just use if for simple separation?

It's cheap.

I don't find HPLC silica that much cheaper than reverse phase for prep columns of same particle size, however it's also:-
- easily transferrable from existing TLC and Flash chromatography data.
- works for many stable lipids, fuels, fat-soluble compounds.
- uses cheap ( but not as cheap as water ), volatile ( can be evaporated quickly at lower temperature ), and lower viscosity ( faster flowrate ) solvents.
- gives consistent separations when water content is controlled.
- readily availably in larger particle sizes that can be used in larger-diameter, lower pressure flash systems ( eg 75 - 400 mm Biotage cartridges ).

In response to your questions,


It depends on the product and regulatory environment.
Prep HPLC columns are usually used multiple times, but lower cost Flash cartridges ( eg Biotage ) are often used in an SPE mode to remove junk as well as resolve analytes, so are one-time-only, but can be multiple use if method and sample cleanliness are appropriate.

If it's possible to retain junk, you can perform multiple runs, then run a flush cycle ever 5 - 10 runs. I often do that for both normal phase and reverse phase preparative HPLC. Saves solvent and time.

As noted above, controlling sample cleanliness, mobile phase water content, using a good flushing solvent, and recognizing the longer equilibrium times, will allow normal phase silica chromatography to be almost as consistent as reverse phase.

If you pay for a preparative HPLC column, you're paying for the ability to produce consistent and repeatable separations on that column for many cycles - I'd be annoyed if a preparative column didn't last 500 runs on a clean sample.

Bruce Hamilton

thanks a lot.

I don't find HPLC silica that much cheaper than reverse phase for prep columns of same particle size, however it's also:-
- easily transferrable from existing TLC and Flash chromatography data.
- works for many stable lipids, fuels, fat-soluble compounds.
- uses cheap ( but not as cheap as water ), volatile ( can be evaporated quickly at lower temperature ), and lower viscosity ( faster flowrate ) solvents.
- gives consistent separations when water content is controlled.
- readily availably in larger particle sizes that can be used in larger-diameter, lower pressure flash systems ( eg 75 - 400 mm Biotage cartridges ).

In response to your questions,


It depends on the product and regulatory environment.
Prep HPLC columns are usually used multiple times, but lower cost Flash cartridges ( eg Biotage ) are often used in an SPE mode to remove junk as well as resolve analytes, so are one-time-only, but can be multiple use if method and sample cleanliness are appropriate.

If it's possible to retain junk, you can perform multiple runs, then run a flush cycle ever 5 - 10 runs. I often do that for both normal phase and reverse phase preparative HPLC. Saves solvent and time.

As noted above, controlling sample cleanliness, mobile phase water content, using a good flushing solvent, and recognizing the longer equilibrium times, will allow normal phase silica chromatography to be almost as consistent as reverse phase.

If you pay for a preparative HPLC column, you're paying for the ability to produce consistent and repeatable separations on that column for many cycles - I'd be annoyed if a preparative column didn't last 500 runs on a clean sample.

Bruce Hamilton