Each vial of RM 8671 contains 800 μL of a nominal 10 mg/mL IgG1κ monoclonal antibody (NISTmAb) in 12.5 mmol/L L-histidine, 12.5 mmol/L L-histidine -HCl- (pH 6.0) (Formulation Buffer). RM 8671 is packaged and supplied to the user in internal threaded polypropylene cryovials which have been double packaged in a cardboard box with an insert designed to securely fit the cryovials, and sealed in a laminate foil pouch to prevent CO2 ingress. The double packaged RM is shipped on dry ice and should remain frozen during shipment. The material should be stored in a frozen state at −80 °C immediately upon receipt and in all cases storage of the material at −80 °C is preferred. In reality, no fill volume/format will be amenable to all assays and end user purposes. Therefore, a series of stability samples (preparation described in ESM) were evaluated to determine the most extreme storage conditions (referred to here as alternative storage conditions) under which the sample yielded a measurement result within ±3uc for a given method.