CHARACTERIZATION OF HAPTEN BINDING TO IMMUNOCONJUGATES BY ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

Electrospray ionization mass spectrometry (ESI-MS) has been used to ch aracterize the covalent binding of different haptens to the enzyme glu cose 6-phosphate dehydrogenase. The technique allows one to directly o bserve the relative amounts of each conjugated species present in a mi xture, as well as the average hapten number. These measurements are us eful for optimizing reaction conditions to yield a more precisely defi ned product for use in immunoassays. The results obtained show that ES I-MS with a quadrupole analyzer can be successfully used to analyze mi xtures of derivatized proteins in the molecular weight range of 50-60 kDa, where the modifying hapten has a molecular weight as low as 130 D a.