Hello, the RI detector is usually used for the analysis of molecules with weak or no UV absorption. Typically applications are alcohols, sugars, sacharides, fatty acids and polymers.

Best regards,

Laurent

RI is limited to isocratic analysis only (not gradient) so it is very important to flush columns down with stronger solvents (then used in the method) after each run. RI detection is based on a physical change in refractive index alone, between the sample and the mobile phase, but it can be used to detect sample with or without a chromophore (*commonly used to detect samples which do not have a chromaphore).

There are several standard test methods that use HPLC with RI detection like ASTM D6591 - 11  Determination of Aromatic Hydrocarbon Types in Middle Distillates ASTM D6379 - 11 Determination of Aromatic Hydrocarbon Types in Aviation Fuels and Petroleum Distillates also see the attached links.

http://pubs.acs.org/doi/pdf/10.1021/ef000072b

http://www.agilent.com/cs/library/applications/5991-3170EN.pdf

RI detector is applicable for the molecule which has no cromophore or uv absorbable capability.