Dear Patrycja Gołębiowska many thanks for your interesting technical question. Die you follow a literature procedure? Normally the work-up procedure of reactions with Grignard regents requires the use of dilute acid to liberate the end product and dissolve the magnesium ions. If you carried out the reaction in diethyl ether solution you can pour the reaction mixture on ice and wash the diethyl ether phase with dilute hydrochloric acid. Then you can wash with carbonate solution and water, and finally dry the solution of your product e.g. over anhdous CaCl2 or Na2SO4. For some general information please see e.g. the following useful link

Grignard Reaction Reagent Mechanism and Cheat Sheet

http://leah4sci.com/grignard-reaction-reagent-mechanism-and-cheat-sheet/

You just need to make sure that your final product is not sensitive to acids.

Good luck with your research! 👍

Do you want to perform the 2nd step in a one pot procedure?

Usually I wash with ammonium chloride. To trap Mg without washing you could try to form a complex with oxalate or tartrate. It would be helpful to have additional information to give you more advice.

Ammonium chloride solution

To get rid of magnesium ion from the reaction mixture by EDTA chelation.

Crystallization separation or add a small amount of ammonia and then sodium pyrophosphate to precipitate magnesium ions.