Problem during evaporation/reconstitution step afetr L/L

[geget]

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

[Peter Apps]

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

[geget]

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.

[Don Shelly]

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