A set of at least two different protein conjugate preparations, each protein conjugate preparation comprising histidine as a buffering agent and a protein conjugate comprising one or more immunoglobulin moieties conjugated to a carrier protein wherein the immunoglobulin moieties of each element of said set of protein conjugate preparation have identical complementarity determining regions (CDRs) and wherein different protein conjugate preparations differ in that the immunoglobulin moieties of the protein conjugates have different CDRs.
