Imperial Oil Ltd., Sarnia, Ontario
(Received 26 February 2001; accepted 24 July 2001)
The refractive index at a given temperature is an important specification parameter for a large number of petroleum products as well as various paraffinic, olefinic, and aromatic hydrocarbon solvents. It is an easy and quick test method to assure the quality and identity of a specific material. Historically, refractive index and refractive dispersion have been measured using manual refractometers. The advent of digital automatic refractometers has made the measurement of refractive index much easier. An interlaboratory study was conducted in 1996 to determine the precision of automatic refractometers and to compare the results with manual instruments. The study involved eight different samples, ten laboratories that used automatic instruments, and six laboratories that used manual instruments, using ASTM D 1218, Test Method for Refractive Index and Refractive Dispersion of Hydrocarbon Liquids, at 20°C. The repeatability of both automatic and manual refractometers was determined to be 0.0002. The reproducibility of both automatic and manual refractometers was determined to be 0.0005. The study showed that there was no statistically significant difference between results obtained with automatic and manual refractometers using ASTM D 1218 at 20°C at a 95% confidence level.
Paper ID: JTE12293J