a method is provided for sequencing peptides and proteins in which the coupling and cleavage reagents are supplied through a valve block assembly with internal delivery channels and a common outlet channel . the outlet channel communicates with a reaction chamber in which the sample is placed . access of reactants to the delivery channels is controlled by diaphragm valves , preferably equipped with relief grooves to accommodate deformation of the diaphragm . reservoirs feeding the delivery channels have an inert atmosphere controlled by pressurizing and venting channels in the valve block . exposure of plastic tubing to oxygen is kept to a minimum . reactants are thereby supplied without significant cross - contamination or oxidative decomposition .