Introduction Centrifugal Techniques

The introduction of gel permeation chromatography materials and ultrafiltration membranes has provided powerful techniques which give very good fractionations on the basis of molecular size. Both techniques are now widely used, and although less popular, centrifugation is available as an alternative independent technique. 

Separation of albumin from globulin, originally done by filtration, was greatly facilitated by Kingsley s introduction of the ether technique (K20). Ether is added to the salt-protein mixture, which is then repeatedly mixed by inversion for 20 seconds and subsequently centrifuged. Flotation of the globulins ensues, and the albumin fraction separates as a subnatant solution. 

The early sixties were golden times for the progress of investigation techniques in this field of science the first NMR studies in the anisotropic media of lyotropic liquid crystals [48] were done, the introduction of the freeze fraction technique for the preparation of electron microscopy probes (e.g., of cell membranes [49]) and the separation of different lyomesophases by centrifugation [47] were introduced all between 1960 and 1962. 

The introduction of centrifugal sedimentation makes the technique capable of determining the distribution of particles below 5 pm. The lower limit depends on the centrifugal velocity. The time of analysis is reduced drastically and multiple samples in cells can be analyzed simultaneously. 

Additional methods to measure crystal size distribution based on particle mass employ light scattering/diffraction methods. Simultaneous measurements of particle size (based on particle volume) and their number are also carried out by Coulter counters. There are a variety of other techniques, based on centrifugal sedimentation, electroacoustic spectroscopy, microelectrophoresis, gravitational sedimentation, scarming electron microscopy, etc. An introduction to these techruques is available in a NIST (National Institute of Standards and Technology) publication by Jillavenkatesa et al. (2001). 

The introduction of these potentially useful techniques is largely due to Ito in 1981. These methods involve CCD and eliminate the need for solid supports. One of the principal advantages is the speed of operation—the separation time (and consumption of solvent) approximating the level of HPLC in one instance involving the isolation of plant hormones by toroidal coil planet centrifugation. 

---