PRINCIPLE OF SEPARATION
See chapter LOC-500
METHOD
The whole equipment consists of a Liquid Overflow Centrifuge (1) and a recyclesystem (6) that makes it possible to work continuesly with a large amount of heavy liquid based on dijodomethano. The heavy liquid is coming from a tap (2). Before starting the sample is mixed in large stainless steel containers with heavy liquid (d=3.0). Turn on the centrifuge (under the work top) and set the number of revolutions (see the schedule on the back wall). The separation procedure is the same as described in chapter loc50. Use a large funnel (5 cm high) on the top of the centrifuge. Because the float will be much more it flows directly into the filter unit (3). The 4-way valve (4) determines the direction of the filtered liquid coming from the float:
• Pure heavy liquid. (90° clockwise).
• After washing the float: high concentrated heavy liquid with acetone. (90° anticlockwise).
• After washing the float 3 times: low concentrated heavy liquid with aceton (180° anticlockwise).
Because the whole system is under vacuum the liquid will be separated from the solid float and flows to a buffer
Firstly, the density of the heavy liquid has to be checked .Draw off some liquid and measure the density with the density gauge. Density should be 3.0 g/ml. If this deviates, draw a larger quantity (as much as is thought necessary), and add dijodomethano or dichlorobenzene accordingly. Use the mixer for better homogenising.
The filters of the two filtering units have to be assembled: the 5 l. unit, 2 paper filters (520 quality) and gauze in between. The 250 ml. unit one filter.
The main switch of the centrifuge is on the backside of the chest. The number of revolutions is set on 5000 rpm and the brake on 8. Place the centrifuge cup into the centrifuge and on top of this the overflow pipe (with outlet to filterunit 5 l.) with the lid and funnel (see text above the centrifuge for funnel size). Let down the security clamp. This prevents the centrifuge from getting open during rotating. Then start the machine with the red button (power) on the operating panel. The button 'heavy liquid' (yellow) is also pressed on the same panel.
Now the sample is transferred to the stainless steel mixing beaker(s). Don't fill more than 1/3 of the contents. Add a little more of the heavy liquid so that the sample/liquid proportion is about 40/60. Stir the sample well to have everything in suspension and to avoid lumps.
The centrifuge is started. At the rotation speed of 5000 rpm so much clear heavy liquid is poured into the funnel that the heavy liquid flows out of the outlet. Immediately the (well stirred) sample is poured into the funnel. Perform those actions quickly one after the other. Rinse the sample beaker once more with heavy liquid and then rinse the funnel with ample heavy liquid (empty the funnel entirely when rinsing it). When the funnel is empty, and the liquid flow from the outlet has practically stopped, the centrifuge can be switched off. Meanwhile the heavy liquid is filtered and pumped to the storage vessel. If filtering is too slow, the compressed air unit (max. 2 bar) can be connected. A lid with a compressed air connection should then be fixed with clamps. Never do this in combination with the (other) 0.5 l filter unit.
As soon as the centrifuge has stopped rotating, disassemblance can be started. Collect all parts in a developer tray and rinse with warm demi water.
The centrifuge cup is taken out and poured over the 500 ml. filter unit. (Do not do this if compressed air is on the other unit!) Don't forget to switch off this unit.
When the float has been filtered it has to be emptied out and transferred to a bucket with demi water for cleaning. Write on the bucket the sample number and the text 'wash' followed by 1 score.This is to indicate that the float is cleaned for the first time. Pour the upper liquid as soon as it is clear. Clean 5 times in total with demi water and stir well (with the big mixer e.g.). Score after every cleaning after 'wash'. After the cleaning the float will be dried in an oven and stored away.
Clean the sink in a stainless steel bowl in the same manner (a 32 µ sieve and a shaking appliance could be used). Drying, however, should occur at a temperature of not more than 50 C.
Catch the cleaning liquid and collect it in a developer tray.
CLEANING
All parts of the centrifuge, as well as the work top have to be cleaned very well. Switch off the vacuum pump.