Question: I was running a method using an ammonium acetate based mobile phase and decided to clean the column. I flushed it with acetonitrile but noticed the column pressure was higher than before when I returned to my method. What happened?
Answer: The problem is most likely the solubility of ammonium acetate in pure acetonitrile. We do not generally recommend using pure acetonitrile as a washing solvent for this reason. When the acetonitrile was introduced to the column, the ammonium acetate that was inside of it may have precipitated. This creates blockages and therefore higher pressures.
What you can try is to reverse the column flow direction and flush with a high water content mobile phase to try to dissolve and remove the ammonium acetate.
For proper Cogent Diamond Hydride™ washing protocols, click here.
