Buffer R (10x) is a 10x concentrated Strep-Tactin® regeneration buffer containing HABA (2-[4'-hydroxy-benzeneazo]benzoic acid). HABA displaces desthiobiotin from the modified biotin-binding pocket of Strep-Tactin® after protein elution. Upon binding of HABA to Strep-Tactin®, the yellow buffer turns red, indicating regeneration and column activity. Please note that 10x Buffer R cannot be used for the regeneration of Strep-Tactin®XT resins, but it can be used to monitor the resin's activity status after the regeneration.