NEB sells two versions of the enzyme, PNGase F (NEB #P0704) and PNGase F (Glycerol Free) (NEB #P0705). The two versions of the enzyme have identical activity, specificity and concentration. The only difference between the two is that PNGase F is stored in 50% Glycerol, while PNGase F (Glycerol Free) does not contain glycerol in its storage buffer. PNGase F (Glycerol Free) is recommended when downstream analysis will include HPLC and/or Mass Spectrometry due to the fact that glycerol is not tolerated in such instruments. Glycoprotein Denaturing Buffer (containing SDS and DTT) is not compatible with Mass Spectrometry applications, and often times hard to remove from the reaction. Therefore, we recommend using PNGase F (Glycerol Free) under non-denaturing conditions if HPLC or MS will be used for downstream analysis. Non-denaturing conditions often require more enzyme units and a longer incubation time.