Browning products of the reaction of PPO, catechol and glycine
was clarified by passing through Na2SO4 anhydrous and centrifuged.
The supernatant was subjected to either scanning for
visible-spectral analysis or LC–ESI–MS analysis by Waters,
Acquity UPLC H-Class instrument equipped with TQ triple quadropole
ESI-MS detector and Acquity UPLC BEH C18 2.1 50 mm column
contains trifunctional C18 stationery phase (1.7 lm particle
size, 185 m2
/g surface area and 0.7 mL/g pore volume). Mobile
phase was methanol water (1:1 volume ratio) at flow rate
0.5 mL/minute. ESI–MS was performed at both ES and ES+ modes
with scan 100–1000 m/e.