A device (100, 800) for measuring absorption of infrared radiation by a protein sample, the device (100, 800) comprising: a source of infrared radiation; a sample holder positioned to place a protein sample in a location to receive infrared radiation from the source; a Fabry-Perot interferometer positioned to receive infrared radiation originating from the source and passing through the protein sample, the Fabry-Perot interferometer comprising a pair of spaced-apart reflective surfaces, at least one of which is movable to change the spacing between the reflective surfaces; a detector positioned to receive infrared radiation from the Fabry-Perot interferometer and to produce an output signal indicating the intensity of the infrared radiation received at the detector; a first band pass optical filter (108, 801) positioned in an optical path of the device such that infrared radiation from the source passes through the first band pass optical filter before reaching the detector; a second band pass optical filter (108, 802) that passes infrared radiation in a second wavelength band different from the first wavelength band; a mechanism for removing the first band pass optical filter (108, 801) from the optical path and placing the second band pass optical filter (108, 802) in the optical path such that infrared radiation from the source passes through the second band pass optical filter (108, 802) before reaching the detector; and a controller coupled to the source, the Fabry-Perot interferometer, and the detector, the controller including a processor programmed to: cause the Fabry-Perot interferometer to be tuned to a first series of different resonant wavelengths with the first band pass optical filter (108, 801) in place in the optical path and to a second series of different resonant wavelengths with the second band pass optical filter (108, 802) in place in the optical path; receive the output signal of the detector at each of the series of resonant wavelengths; and record an absorbance spectrum indicating the absorbance of the protein sample as a function of infrared radiation wavelength. a source of infrared radiation; a sample holder positioned to place a protein sample in a location to receive infrared radiation from the source; a Fabry-Perot interferometer positioned to receive infrared radiation originating from the source and passing through the protein sample, the Fabry-Perot interferometer comprising a pair of spaced-apart reflective surfaces, at least one of which is movable to change the spacing between the reflective surfaces; a detector positioned to receive infrared radiation from the Fabry-Perot interferometer and to produce an output signal indicating the intensity of the infrared radiation received at the detector; a first band pass optical filter (108, 801) positioned in an optical path of the device such that infrared radiation from the source passes through the first band pass optical filter before reaching the detector; a second band pass optical filter (108, 802) that passes infrared radiation in a second wavelength band different from the first wavelength band; a mechanism for removing the first band pass optical filter (108, 801) from the optical path and placing the second band pass optical filter (108, 802) in the optical path such that infrared radiation from the source passes through the second band pass optical filter (108, 802) before reaching the detector; and a controller coupled to the source, the Fabry-Perot interferometer, and the detector, the controller including a processor programmed to: cause the Fabry-Perot interferometer to be tuned to a first series of different resonant wavelengths with the first band pass optical filter (108, 801) in place in the optical path and to a second series of different resonant wavelengths with the second band pass optical filter (108, 802) in place in the optical path; receive the output signal of the detector at each of the series of resonant wavelengths; and record an absorbance spectrum indicating the absorbance of the protein sample as a function of infrared radiation wavelength. cause the Fabry-Perot interferometer to be tuned to a first series of different resonant wavelengths with the first band pass optical filter (108, 801) in place in the optical path and to a second series of different resonant wavelengths with the second band pass optical filter (108, 802) in place in the optical path; receive the output signal of the detector at each of the series of resonant wavelengths; and record an absorbance spectrum indicating the absorbance of the protein sample as a function of infrared radiation wavelength.