Cogent TYPE-C™ columns including the Cogent Diamond Hydride have a very low background noise even when used with LC-MS and the white film most likely comes from ammonium acetate build up from your mobile phase.
These columns have been proven to be extremely durable and because of the direct silicon-carbon bonds of these phases, bonded phase bleed is almost non-existent.

     For symptoms of packing material loss or bonded phase hydrolysis, click here.