The specificity of the anti-bass IgM monoclonal antibody (mAb) was rigorously validated by immunoprecipitation coupled with mass spectrometry (IP-MS). This analysis confirmed the mAb’s selective binding to IgM while identifying potential off-target interactions, ensuring its suitability for IgM depletion applications. The mass spectrometry data provided high-confidence evidence of target specificity and revealed no significant cross-reactivity with non-IgM proteins.