a valve block assembly with internal delivery channels and a common outlet channel is provided . 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 . the assembly is particularly adapted for use in a dna or protein sequencer to supply reactants without cross - contamination or oxidative decomposition .