Optilab rEX refractive index detector combines semiconductor photodiode technology and proprietary computer algorithms. Users can view the full range of instrument detection at all times. The dn/dc of a solvent can be measured at the same wavelength of light as a light scattering instrument, enabling absolute molecular weight determinations. The absolute refractive index of a solution can be measured, an option that is not possible with any other on-line RI detector. The instrument reaches temperatures that are below and above ambient. Temperature control can be programmed to as low as 4 C or as high as 50 C and is compatible with all HPLC systems.