In this direct method α-amylase catalyzes the hydrolysis of 2-chloro-p-nitrophenyl-α-D-maltotrioside (CNP-G3) substrate at pH 6.0 forming 2-chloro-p-nitrophenol (CNP) and free glycosides.
The reaction is monitored kinetically at 405 nm by the rate of formation of the colored CNP produced, proportional to the activity of the α-amylase in the sample.