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Development studies of centrifugal photosedismentometer using laser light

1975; Elsevier BV; Volume: 11; Issue: 3 Linguagem: Inglês

10.1016/0032-5910(75)80051-9

1873-328X

Michael J. Groves, H.S. Yalabik, J.A. Tempel,

Microfluidic and Bio-sensing Technologies

The design and development of a new centrifugal photosedimentometer which uses laser light is described. The new instrument is derived from a previously available commercial device but avoids the use of an electro-mechanical servo system which has been a feature of previous designs. Light from a helium—neon continuous lases is carried with optical fibres to a point above the transparent rotating centrifuge tank which corresponds to a silicon photodiode set underneath the tank. Light from the rear of the laser tube is taken with optical guides to a second photodiode mounted near to the first. The logarithm of the divided voltage output from the two photodiodes is an indirect measure of the optical density at a radius in the rotating tank corresponding to the sensing point. Using the homogeneous suspension technique, particles in the tank are able to sediment according to Stokes' law, and the relationship between the optical density and the time of sedimentation is therefore a characteristic of the particle size distribution of the sedimenting system. Using data logging method the computer treatment of results from the device has been facilitated and may be used for most suspended particulate systems irrespective of the particle density, provided that the particles are large enough to interfere with the light beam and are mobile under centrifugal conditions. The intense monochromatic and coherent character of the laser light has improved the sensitivity of the method, and particles corresponding to an apparent Stokes' diameter of 0.018 μm have been detected in a sample of commercial intravenous emulsion used as a standard for investigational purposes.