An apparatus includes a reaction vessels coupled to an electronic sensor for monitoring a reaction product in the reaction vessel; a fluidics system for sequentially delivering a plurality of reagents to the reaction vessel, the fluidics system including a plurality of reagent reservoirs in fluidic communication via a plurality of flow paths with a fluidics circuit and to a common passage in fluidic communication between the fluidics circuit and the reaction vessel, a solution reservoir in fluidic communication with the common passage via a branch passage connected with the common passage at a junction between the fluidics circuit and the reaction vessel; and an electrode in contact with a solution within the branch passage, the electrode being in electrical communication with the reaction vessel through fluid extending from the branch passage and through the common passage, the electronic sensor generating an output signal depending on a voltage of the electrode.