An analytic separation arrangement includes a system of tubes including a separation zone, preferably a separation column, which tubes upstream the separation zone are connected with reservoirs for a carrier and a chemical sample to be seperated and analyzed, and downstream the separation zone are connected with a waste container for the carrier containing the sample and also are connected with transporting means for the carrier and the sample. The tube system is associated with an optical detector for monitoring changes in the absorption, in the fluorescence or in the optical activity of the carrier when it is transported through the tube system and past the optical detector, which is arranged in the path of the carrier behind the separation zone but in front of the waste container. Between the separation zone and the optical detector there is arranged in the path of the carrier a refractive index equalizing unit. Prior to being transported past the optical detector the carrier, which is comming from the separation zone, is directed through the refractive index equalizing unit, where its refractive index is preferably constantly monitored and where upon detection of changes of the refractive index of the carrier the deviation is compensated by adding to the carrier a compensating agent.