Abstract: The present invention relates to a method of using a storage-stable, pre-stained 3,3′,5,5′-tetramethylbenzidine (TMB) substrate in an enzyme substrate. The TMB substrates comprise: (a) a water-based TMB substrate composition which includes a peroxide, e.g., hydrogen peroxide or urea hydrogen peroxide, and (b) a dye which is soluble therein. Suitable dyes to be included in the substrate preferably have an absorbance at 450 nm of at the most milli absorbance units. Examples of dues are Pholixine B, Eosin B and Quinaldine Red. The substrates are advantageous in that they include a dye which is visible to the human eye. This is especially valuable when the substrates are handled and measured. The substrates are especially suitable for enzyme assays such as enzyme-linked-immunosorbent-assays (ELISA), e.g. horse radish peroxide (HRP) is used. The substrates may advantageously include less than 5% organic solvents and a solubility increasing agent such as polyvinylalcohol.

Abstract: A method of isolating a biomolecule from a medium containing biomolecules by ion exchange wherein the ion exchange material consists of a material having ion exchanging groups which can be transformed from a charged form to an uncharged form; the eluant comprises a charge neutralizing acid or base transforming the ion exchanging groups from the charged form to the uncharged form; and the charge neutralizing acid or base has a concentration in the eluant which is twice, preferably equal to or less than the concentration of the ion exchanging groups of the ion exchange material; the ion exchange material being in a packed, hydrated state. Preferably the method is for the isolation of phosphopeptides from a medium containing casein hydrolysates and the use of such isolated biomolecules is for the production of a food, a feed, a health care product, a cosmetic, or a pharmaceutical.