Abstract: A lyophilized antibody panel is disclosed for interrogation using elemental analysis. The antibody panel includes multiple antibodies each element-tagged or element-labelled with one or more isotopes such that each different antibody is isotopically distinguishable from the other antibodies. Each element tag can include one or more unique isotopes or unique combinations of isotopes. The set of element-tagged antibodies can be lyophilized in admixture. Thus, the lyophilized element-tagged antibody panel can be easily and efficiently resuspended and mixed with a sample prior to interrogation with an elemental analyzer, such as a mass spectrometer. This lyophilized element-tagged antibody panel can provide the benefits of an element-tagged assay while also being easy to use and remaining stable for long durations.