2263
Anal. Chem. 1002, 64, 2263-2266
Method for Determining the Density of Pure and Modified Supercritical Fluids John J. Langenfeld, Steven B. Hawthorne,' and David J. Miller University of North Dakota, Energy and Environmental Research Center, Grand Forks, North Dakota 58202
Joseph Tehrani ISCO Inc.,
P.O.Box 5347, Lincoln, Nebraska 68505
Densities of three pure supercritkal fluids (C02, NzO, and CHCiF2)and one modifled fluid (COz modifled with 5 volume % methanol) were determinedover a wide rangeof pressures (60-600 atm) and temperatures (40-150 "C) using a dmpie device constructed from a conventional supercritical fluid extraction cell. Triplicate measurements showed excellent reproduclbiiitles, with percent reiatlve standard deviations typically ranging from 0.1 to 0.7%. The calculated densities of the pure fluids based on modified equations of state were generallyin good agreementwith experimentalmeasurements (
