a Resorcinol was obtained from Sigma-Aldrich.
b PPD, copper(II) sulfate pentahydrate, hydrochloric acid and methanol were purchased from Merck.
c Hydrogen peroxide was purchased from Fluka.
d Screw cap vials and plastic syringes were purchased from neoLab.
e The Lambda 12 dual beam spectrometer is manufactured by Perkin Elmer.
f UV WinLab software (version 2.80.03) is manufactured by Perkin Elmer.