Medicago AB Products Are Available Worldwide. For Research Use Only. EC-Blue Enhanced Substrate (TMB) Substrate is a ready-to-use liquid substrate for HRP, specially developed for ELISA applications. TMB Substrate turns deep blue (620-650 nm) in the presence of a peroxidase-labelled conjugate. Color development can be stopped by adding 0.5 M H2SO4 (A10-9500-50), which turns the substrate yellow (450 nm). TMB contains a proprietary ready-to-use chromogen substrate mixture. The solution has a straw-yellow color at room temperature and a light greenish tint when stored at 4°C. The color returns to normal when warmed to room temperature. For laboratory use only.