I purified a small molecule with RP-HPLC using 0.01% TFA buffer. Before purification, LC-MS looks correct M+H around 726. However, after purification and lyophilization, M+H became 722. The molecule contains PEG2 and NOTA. While the analogue without PEG2 came out normal without MW change. Could you share some ideas if you have any similar experience or thoughts? Thanks!
The observed MW loss from 726 to 722 after RP-HPLC and lyophilization of a PEG2-containing molecule suggests loss of a PEG unit or other volatile components. Optimize HPLC and lyophilization conditions to prevent future degradation or loss.
A loss of only 4 Da? Doesn't a PEG unit have more mass than that? Is it possible there is a rearrangement happening, losing 4 hydrogens?
Jack Silver 4 Da loss is very weird. I still couldn't figure it out. Thanks for your thoughts.
Maybe there is a loss of a group and also addition of a solvent molecule to make an adduct? The solvent adduct is one of the solvents used in your mobile phase, or maybe K or Na. That could give an odd change in mass.
Thanks everyone for your thoughts. I really appreciate your time and help. It turned out that the mass-spec is off target after abused with tons of samples in a short period of time. The manager calibrated it and now everything looks good. Hope this helps for anyone who had similar issues.
- Badges
- Science topic