Modification of a Differential-Refractometer-Detector for Liquid Chromatography

Detectors with a sensitivity at least of 1 ppm solute in the eluent are wanted for high speed LC. Therefore, usually the noise level of the non-specific differential refractometer detector must be less than 10−7 RI. To achieve this, a heat exchanger must be used to keep the temperature of the mobile phase constant. The usual heat exchangers cause unwanted wide peak broadening. Geometrically deformed heat exchangers 20 cm in length only are described for refractometer detectors. Peak broadening is measured as a function of the flow rate. The noise is less than 3·10−8 RI, and the peak broadening is equivalent to or better than that of a UV-detector with a cell volume of 1 microliter.