In one exemplary embodiment, the present invention is directed to a method that comprises providing a reaction substrate having a plurality of substrate reservoirs adapted to receive a reactant system at least partially embodied in a liquid. A thermal unit maintains the reactant system at a first temperature. A head plate is disposed adjacent to the reaction substrate to form a sealed and pressurized headspace above the substrate reservoirs. The head plate is maintained at a second temperature higher than the first temperature. A second reactant may be introduced as a gas into the headspace above the plurality of substrate reservoirs.