Sedimentation pipette centrifuge

Gravity and centrifugal sedimentation can be combined for the same sample in order to directly determine Stokes diameter for a wide range of particle sizes. In such a way conversion are avoided and a mass distributions, applicable to processes where gravimetric efficiencies are relevant, can be properly derived. Ortega-Rivas and Svarovsky (1994) determined particle sizes distributions of fines powders using a combined Andreasen Pipette-pipette centrifuge method. They derive relations useful to model hydrocyclone separations, which were later employed to describe apple juice clarification. 

Sedimentation in centrifugal field 0.5 pm -10 pm Eritsch Analysette 21 (Anderson Pipette centrifuge)... 

Schweyer (1942) compared various methods of particle-size measurement (except centrifuging). He found excellent agreement between pipette and hydrometer methods. He considers the former the best method for determining the particle-m/.c distribution of sub-sieve material by sedimentation, and prefers the hydrometer as a rapid control procedure. 

Gravitational and centrifugal sedimentation using a pipette is attractive due to its versatility and low capital cost, but the analysis requires a skilled operator and is time consuming. 

A method for the determination of soluble nitro-cellulose in gun-cotton and smokeless powder has been published by K.B. Quinan (Jour. Amer. Chem. Soc. 23 [4], 258). In this method about I grm. of the finely divided dry sample to be analysed is placed in an aluminium cup 1.9 inch in diameter and 4-1/8 inch deep. It is then covered and well stirred with 50 c.c. of alcohol, 100 c.c. of ether are then added, and the mixture is stirred for several minutes. After removing the stirrer, the eup is lightly covered with an almninimn lid, and is then placed in the steel cup of a centrifugal maehine, whieh is gradually got up to a speed of2,000 revolutions per minute, the total centrifugal force at the position oeeupied by the cups (which become horizontal when in rapid rotation) is about 450 lbs. They are rotated at the full speed for ten to twelve minutes, and the maehine is then gradually stopped. By this time the whole of the insoluble matter will be at the bottom of the eup, and the supernatant solution will be clear. It is drawn off to within a quarter of an inch of the bottom (without disturbing the sediment), with the aid of a pipette. 

S. Berg, Determination of Particle Size Distribution by Examining Gravitational and Centrifugal Sedimentation according to the Pipette Method and with Divers, ASTM, Special Technical Publication No. 234, 1958, pp. 143-171. 

Berg, S. Determination of particle size distribution by examining gravitational and centrifugal sedimentation to the pipett method and with divers. Symp. PSA, June 1958, Boston, ASTM STP 234 (1959), p. 143 - 171 /4/ Chung, H. S. Hogg, R. The effect of Brownian motion on particle size analysis by sedimentation. Powder Techn. 41 (1985) 3, p. 211 - 216 /5/ Allen, T. Sedimentation techniques of particle size measurement. Conf. PSA Sept. 1985, Bradford, Proceed, p. 24 - 45... 

Place the tubes in a sand-bath or block heater at 100 C for exactly 30 min (Note a). Remove the tubes and centrifuge the contents for 10 min at 5000 rpm. After centrifuging carefully withdraw the supernatant liquid with a capillary pipette attached to a vacuum source, being careful not to disturb the sedimented material (Note b). 

Due to these disadvantages, especially the long and tedious analysis procediues involved in the pipette methods, sedimentation balance method, and diver method, these widespread devices and methods have been replaced with modem technologies that do not depend on separation. The current versions of sedimentation that are still widely used are primarily centrifugal sedimentation using light or x-ray detection [12]. 

If the pipette tips clog frequently, centrifuge the injection solution in a microcentrifiige at 14,000 rpm for 10-15 minutes to sediment offending particulates. 

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