sentence: The solution was equilibrated to 37 ° C for 5 min , after which 20 μ L of a solution of 3 mM in 2,2 ′ - azobis - ( 4-methoxy-2 ,4 - dimethylvaleronitrile ) ( MeOAMVN ) in acetonitrile was added to each well using the reagent dispenser of a microplate reader .