Electrospray mass spectrometry (ESI-MS) has been used to examine monoclonal antibodies (MAbs), antibody fragments (Fab and Fc), modified fragments and a range of other chemically-modified proteins as part of a study aimed at establishing ESI-MS as a method for the rapid characterisation of conjugated proteins.

This has been approached from two angles. Firstly, ESI-MS of complexes formed between chelators such as diethylenetriaminepentaacetic acid (DTPA) and other small molecules (eg. biotin and iodine) conjugated to hen egg white lysozyme (HEL) (14 kDa) and horse heart myoglobin (MYO) (17 kDa) demonstrate the considerable advantages of this powerful technique compared with existing methods for the characterisation of chemically-conjugated proteins. Secondly, the conditions for ESI-MS of intact antibodies and antibody fragments have been examined in detail, and we have shown that the addition of several biotin molecules to the 50 kDa Fab fragment can be easily detected in ESI mass spectra thus demonstrating the potential for the characterisation of modified MAb fragments and metabolites.

Finally, the strengths and limitations of ESI-MS of intact antibodies are discussed and these results indicate that it may only be possible to detect average shifts in the mass of intact antibodies following modification.