Methods are provided for improved quenching of undesired side reactions upontreating a red blood cell composition with a pathogen inactivating compoundcomprising a nucleic acid binding ligand and a functional group which is, orwhich is capable of forming, an electrophilic group. In some embodiments, theimproved methods use a suitably high concentration of quencher that comprisesa nucleophilic functional group that is capable of covalently reacting withthe electrophilic group, wherein the treatment occurs within a desired pHrange to provide sufficient quenching. Preferred quenchers for use in some ofthe methods include thiols, such as glutathione, which have been suitablyneutralized such that addition to a red blood cell composition results in thedesired concentration of quencher at a desirable pH range of 6.8 to 8.5.
