Optilab rEX (refractometer with EXtended range) uses a combination of semiconductor photodiode technology and proprietary computer algorithms to have the full range of instrument detection always be present, and to provide full sensitivity over the entire range. The instrument has no range or gain settings. Flow cell with a total volume of 7.4 μl minimizes band broadening and provides temperature stability. The online RI detector can measure the absolute refractive index of a solution. Temperature control is easily programmed down to 4 C or as high as 50C. The detector is compatible with all HPLC systems.