An immobilized enzymatic reactor can include a wall defining a chamber having an inlet and an outlet; a solid stationary phase covalently linked to an enzyme and disposed within the chamber; and a pressure modulator in fluid communication with the chamber and adapted to support continuous flow of a liquid sample comprising a polymer analyte through the inlet, over the solid stationary phase, and out of the outlet under a pressure between about 2,500 and 35,000 psi. In one example, the solid stationary phase includes inorganic/organic hybrid particles in an ultra performance liquid chromatography system, the enzyme is a protease, and the polymer analyte is a polypeptide. The immobilized enzymatic reactor can prepare an analyte for applications such as for hydrogen deuterium exchange mass spectrometry.