(180 mL concentrated H2SO4 dissolved in 150 mL H2O, with addition of 9 mL of 1.5 M FeCl3$6H2O), after incubation for 60 min at room temperature in the dark. Optical densities were read at 530 nm.
(180 mL concentrated H2SO4 dissolvedin 150 mL H2O, with addition of 9 mL of 1.5 M FeCl3$6H2O), afterincubation for 60 min at room temperature in the dark. Opticaldensities were read at 530 nm.