Column C18 with a 50:50 hexane and dichloromethane
Posted: Wed Mar 10, 2021 6:34 pm
Can I use hexane and dichloromethane as mobile phase with a c18 column ? 
You can, but that doesn't mean you should (and I don't know why you would want to).
Assuming you are using a reasonably state-of-the art column, you will void any warranty but you probably won't damage the column, but (and it's a big but!) you will have massive equilibration issues. You will have to flush the column extensively with a co-solvent (most commonly this would be isopropanol) to remove all traces of the default mobile phase/storage solvent before switching to your hexane/dichloromethane and allowing that to remove the iPrOH.
The other concern is with the HPLC system itself. It's not uncommon for manufacturers to use different seal materials for aqueous vs. non-aqueous use, so check with your vendor to confirm compatibility.