A method for producing an immunoconjugate, the method comprising combining one or more compounds of Formula I and an antibody of Formula II, wherein Formula II is an antibody with one or more lysine residues, in an aqueous solution buffered at a pH of about 7.5 to about 9 until at least 33 mol% of the one or more compounds of Formula I is conjugated to the antibody of Formula II to provide the immunoconjugate of Formula III, wherein Adj is an adjuvant, Z is –CH2–, –C(O)NH–, –C(O)O–, or –C(O)–, L is a linker, E is an ester, and r is the average number of adjuvants attached to the antibody and is a positive number up to about 8, in a first buffered aqueous solution.
