Chromatography Forum

Dear everyone,

I am working on the determination of mineral Oil Hydrocarbons in complex food matrices, such as olives and Lima beans. Liquid extraction with hexane is used, with on-line epoxidation-HPLC-GC. A silica column is used to separate MOSH and MOAH, then the fractions are transferred to the GC.

The problem is that after a few injections, retention in HPLC begins to change, so I cannot fractionate correctly. I know this is a very complex matter to be discussed in a forum, however any feedback would be greatly appreciated.

What are the solvent for the HPLC with the silica column?
Is it isocratic?

Could it be the known issue of normal phase chromatography, that the silica stationary phase cumulates water from your solvent, which at some point alters the retention?

Maybe you could install an additional silica column to trap the water of your eluents prior to your injector or on each solvent line before the gradient prop. valve.
Or filter your solvent through silica or molecular sieve (3A/4A) and attache a "moister catcher" (tube with silica or molecular sieve) to your solvent bottle to keep it dry.

It was exactly that! Thank you very much for your answer!

glad it helped and thanks for reply.

What have you done to solve the issue?
So others may learn as well.