Bromophenol Blue Method- method for monitoring the coupling in the solid phase peptide synthesis (or any solid phase amide bond formation).
The method uses the coloration of the resin containing the free amino groups by solution of bromophenol blue in DMF containing HOBt (to eliminate the basicity of DMF). Amount of the dye used for the monitoring should not exceed 1% of the molar amount of the amino groups available on the resin. The blue resin is then exposed to coupling reagent and decolorization of the resin indicates completed coupling. Coupling reagents requiring addition of the base are not compatible with this monitoring technique. This method is especially suitable for library synthesis monitoring since it allows simultaneous evaluation of coupling progress in multiplicity of reaction vessels without the necessity to open reactors and take samples.