A combined dual pump-injector valve utilizing a single piece of material to house the barrel for each of the two piston-based pumps and to provide the stator of the associated valve, thus eliminating any need for connections between the pumps and the valve, and therefore eliminating the potential for high-pressure leaks or pressure reductions. The combined dual pump-injector valve permits injection of nanoliter-sized samples into a chromatographic column such that complete analyses can be completed with microliters of mobile phase with nanoliters of a sample.