text: A differential refractometer (DRI), or refractive index detector (RI or RID) is a detector that measures the refractive index of an analyte relative to the solvent.  They are often used as detectors for high-performance liquid chromatography and size exclusion chromatography.  They are considered to be universal detectors because they can detect anything with a refractive index different from the solvent, but they have low sensitivity.