A simple and reliable system for measuring the refractive index of liquids using a position-sensitive detector

A simple and yet efficient apparatus for the measurement of the refractive index of liquids has been developed, with the purpose of controlling adulteration in liquids of everyday use. In the system, the index of refraction of the liquid under test is determined by measuring the lateral displacement of a laser beam, that passes obliquely through a rectangular cell filled with the liquid under characterization. The lateral displacement is accurately determined by a position-sensitive detector. A careful analysis of the errors that can be obtained with the system has been carried out, that yielded calibration curves for easy on-line correction. To characterize the performance of the system, a series of tests has been performed on simple liquids, under controlled conditions. The residual errors have proven to be within one part over 10³. The proposed system is suitable for easy automation, obtaining simple and accurate measurements that can be performed also for volatile compounds