Chromatography Forum

Hi everybody, i am a new user on this chromatography forum.

I will try to explain my problem :

I have a difficulty with the last step evaporation/reconstitution under nitrogen after L/L extraction of serum/plasma. After evaporation, i can see a depot in the tube (i think it’s normal). But after reconstitution, i can’t resolubilise this depot and the solution is not limpid.

Anyone can give me a idea to solve my problem, or an advice.

More precision :
I work with a LC-MS/MS in reversed phase with a gradient of methanol in water, in therapeutic drug monitoring of antiepileptics.
The extraction solvant i evaporate is a mixture of acetonitrile and ethyl acetate.
The reconstitution solvant is a mixture of methanol/water (solvant used in the chromatography). I can’t use more than 30% of methanol in reconstitution solvant because of apparition of an “elutropic effet”.

Thank you for your help

Welcome.

As long as the reconstitution solvent extracts the analytes form the deposit, the presence of the deposit is not per se a problem.

Do a recovery experiment - if recoveries are repeatably good you do not need to worry about the deposit.

Peter

Thank you for your answer.

Ok for the recovery experiment. I will try.

In fact, the initial method developed in our laboratory does not necessitate evaporation/reconstitution. Direct injection of L/L extraction solvent works well. But the migration of the method from HPLC to UPLC force us the change the injection solvent. That's the reason.

The precipitate that you see is from the ethyl acetate. It should be soluble in polar solvents. It is highly flammable.