Flow-Throuk Density Meter for Zonal Centripugation and Other Procedures

The instrument is based on the principle that the transmission of beta-particles through a fluid is a function of density. The fluid flows through a 3mm diameter cylindrical channel in a perspex block and passes between a 1 milliCurie 90_Sr/ 90_Y ceramic bead point source and a plastic phosphor optically coupled to a photomultiplier. The signal is amplified and displayed on a countrate meter coupled to a paper chart recorder, Facilities for zero suppression and scale expansion of the countrate meter reading are provided. The instrument whioh was designed originally for zonal centrifugaticn, has been used to monitor sucrose (ρ 1.0–1.3) and caesium chloride (ρ 1.0–1.8) solutions at flow rates up to 50ml/min. The accuracy attained is normally better than ± 0.1% of density at any point in the range. The instrument has also been used with success to monitor gradients in isoelectric focusing (personal communication from K. B. Cooke of the Westminster Hospital Medical School). 1. R. S. Atherton, P. Hawtin and P. Hutchinson, Anal Biochem., 49, 326 (1972)