A new class of mass-tag polymers is provided, which include enriched metal isotopes such as zirconium and hafnium mass tags. The chemistry of these new mass tags are different from that of lanthanide mass tags, and opens up new mass channels that can be used in mass cytometry. These polymers may be used for mass cytometry, therapeutic delivery of a radioactive isotope, or screening of a therapeutic isotope. Aspects include a kit, method of making, and method of using a polymer, isotopic composition, or both. A kit may include a polymer. The polymer may include pendant groups that chelate an enriched isotope, such as zirconium and/or hafnium. The kit may include an isotopic composition comprising an enriched zirconium or hafnium isotope. Polymers may be conjugated to a biologically active material. Aspects may also include making a kit. Aspects include use of a kit, such as for mass cytometry.