RI Detector HPLC

A refractive index (RI) detector is a widely utilized instrument in chromatography, especially in high-performance liquid chromatography (HPLC). Its operation is based on monitoring variations in the refractive index of a mobile phase caused by the elution of analytes.

The fundamental principle underlying the detector is refraction, the bending of light as it passes through mediums with diverse refractive indices. In the detector’s optical path, the sample, typically a liquid containing separated analytes, flows through a transparent flow cell. This flow cell facilitates the interaction of the sample with incident light.

The RI detector employs two beams of light—a reference beam and a sample beam. The reference beam flows through a cell filled with the pure mobile phase (devoid of analytes), while the sample beam passes through the flow cell containing the analyte-laden sample. As the mobile phase, containing eluting analytes, moves through the flow cell, the refractive index of the solution undergoes changes. The presence of analytes modifies the optical properties of the mobile phase, resulting in a refractive index alteration. The two beams, originating from the reference and sample cells, are combined. The interference between these beams is detected and quantified.

Variations in the refractive index of the sample beam, induced by the presence of analytes, cause fluctuations in the interference pattern. The detected interference pattern is transformed into an electrical signal, which is subsequently processed and recorded. This recorded signal directly corresponds to the concentration of analytes in the sample. It is critical for any RI application that the mobile phase remains isocratic to ensure that the reference beam is always the same. Any refraction of light is caused due to the sample components and not varying mobile phase composition.

In summary, a refractive index detector functions by leveraging alterations in the refractive index of the mobile phase as analytes elute through a flow cell. The interference between reference and sample beams is harnessed to identify changes in the refractive index, subsequently translating these alterations into an electrical signal. This mechanism proves particularly valuable for compounds lacking strong UV absorbance, addressing a limitation in UV detectors.

Consumables and spares:

  • SCION 6450 RI Detector
  • Flow cell unit (LC20210224)

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