Can pH of a His buffer change during lyophilization?

[Dhh1994]

We lyophilized 50mg/ml mAb with PI of 7.5 in a 10mM His buffer pH 6.2. Upon reconstitution the pH is 6.5. Does anyone have an explanation for this? I am under the impression His is much less susceptible to pH change during lyophilization as opposed to something like a phosphate buffer. Thanks.

 

[epenguin]

I cannot answer from direct experience or knowledge. A quick look showed that there is quite a lot of literature on stability and lyophilisation of proteins, naturally. I would think that this is a small pH change is not a worry in itself. For average readers of this forum, mAb probably means monoclonal antibody.

To attempt to reason about it (no promise) it is not enough to tell us ‘His’ (histidine) buffer. You would have to tell us how it is made up. E.g. whetherstarting with histidine or histidine hydrochloride or other salt, and brought to pH with what?