Systems and methods for analyzing multiple samples in parallel using mass spectrometry preferably coupled with fluid phase separation techniques are provided. A modular mass spectrometer includes a vacuum enclosure, multiple sample inlets, multiple common vacuum pumping elements, and multiple mass analysis modules disposed substantially within the enclosure, with each module preferably including a mass analyzer and a transducer. In one embodiment, the modules mate with the vacuum enclosure to define multiple sequential vacuum regions, with each vacuum region having an associated common vacuum pumping element. At least one multi-pole ion transfer optic element is preferably associated with each module. Fluid phase separation devices may include microfluidic devices utilizing chromatographic, electrophoretic, or other separation methods.