Color test for the detection of resin-bound aldehyde in solid-phase combinatorial synthesis

We report the development of a sensitive and specific color test for the detection of the presence of resin-bound aldehyde groups using 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald). Aldehyde resin turns dark-brown to purple after a 5 min reaction followed by a 10 min air oxidation period. Resins that possess other functional groups (i.e., ketone, ester, amide, alcohol, and carboxylic acid) do not change color under the same conditions. The detection limit is 20 micromol/g for polystyrene-based aldehyde resins.