How to extend the signal duration of Homemade ECL
 

I have made the homemade ECL like this:

Solution A (50ml):
50 ml 1mM Tris pH 8.5
110 ul 90 mM coumaric acid (0.2mM coumaric acid)
250 ul 250 mM Luminol (final 1.25mM Luminol)

Solution B (50ml)
50ml 100mM Tris 8.6
35ul 30% H2O2

To use, mix 500ul Solution A and Solution B.

I found this homemade ecl could generate signal with a short duration (less than 3mins). How could I extend the duration? thanks!