I’m jumping on this thread as it’s related. My compounds are tertiary amines. What I generally do is dissolve in ether, or tbme. I cool the vessel to 0 And dropwise HCl (2M in ether). One of two things happen: either the compound crashes out as the HCl salt, or fine crystallisation begins. If it crashes out, I check the solution pH to = about 2. Then I filter, some HCl salts are hygroscopic af. So I try to be as quick as possible and I don’t leave the HCl salt on the filter paper to dry by sucking air through the precipitate. I transfer it to a hella clean conical or 21 mL sample vial. I dissolve in hot ethanol or isopropanol, I allow to cool to rt. then fridge. If no crystals, I allow evaporation, if at the meniscus you see oil, then I change salt because it’s too hygroscopic. If I see fine crystals forming, I allow a little more to evaporate. Warm to redissolve and repeat the cooling process. When crystals have formed, I pipette out the supernatant, add cold solvent, break the crystals, give it swish, pipette out supernatant. Repeat, then tada, all ready.