PlatinumLink protein labeling kits are used to label purified (recombinant) proteins for downstream applications. The kits offer the ULS labeling molecule bound to biotin, DNP, fluorescein or rhodamine for direct labeling of proteins. The kits include ULS-Trap purification columns, which ensure complete removal of un-reacted label while yielding high sample recovery independent of protein size. ULS technology provides a high coverage of the proteome through the specific labeling of methionine, cysteine and histidine residues.