 Refractive index detector

A refractive index detector measures the difference in refractive index between a sample stream and a reference. In liquid chromatography, a solute passing through the detector can change that difference and produce a signal.

The signal depends on both solute concentration and the solute's refractive-index increment relative to the solvent. Temperature drift or changing mobile-phase composition can also shift the baseline, so a peak is not automatically a substance-specific identification.