I am currently working on a purification kind of MAb. Its PI is 6.11. in one step of process I have to decrease its pH near 5.2 because of some considerations. The base of buffer is tris-HCL. data was shown that by decreasing pH acidic isoform will be increased. Could any one help me regarding this process I mean introduce some amino acid or changing the base of the buffer
Regards
Tris is not a useful buffer at pH 5.2 because its pKa is 8.1. You should add a buffer that has a pKa near 5.2. MES is one such buffer (others can be found here: http://www.sigmaaldrich.com/life-science/core-bioreagents/biological-buffers/learning-center/buffer-reference-center.html). Since the sample already contains a Tris buffer, you will have to overcome its buffering capacity. You can do this by adding the low pH buffer at a higher concentration than the Tris buffer, and you may also need to use buffer at a slightly lower pH than 5.2. A little experimentation with the buffer solutions and a pH meter should reveal what the right low pH buffer pH should be to get the desired final pH, using the same concentrations and volume proportions as you will use for the MAb.
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