hello, what is the role of methanol and phosphoric acid in the...

This Assay is done with blue acid dye. The phosphoric acid generates the acidic environment. This (and beeing bound to protein) is needed to shift of the acid dye (e.g. coomassie G250) absorbtion maximum from 465 nm to 595 nm . After that, you are able to measure the protein´s concentration at 595 nm.