An investigator is often faced with the problem of separating particulate matter from small variable volumes of valuable (in terms of time and previous effort) material. With Beckman fixed-angle rotors and adapters, as little as 2 ml of solution may be centrifuged, but use of less than this results in tube collapse. With Beckman swinging-bucket rotors and an adapter, as little as 0.8 ml may be centrifuged. Again the investigator is limited to a fixed volume to prevent tube collapse. A lighter immiscible liquid may be used to fill the tube completely and prevent tube collapse but this is often undesirable, particularly if the supernate is to be saved.
Since rotors with adapters may not be operated above 50,000 rpm and since the adapter moves the geometric center of the sample toward the center of rotation and regions of lesser centrifugal force, the times of centrifugation with these adapters are usually longer than with the larger volumes and the normal tube.
One obvious way to use variable volumes and maximum centrifugal force would be to employ a swinging-bucket rotor and tubes cut to a length only 2 or 3 mm longer than that required to hold the sample. Of course, some method would have to be devised to extract this short tube from the bottom of the bucket. It is the purpose of this communication to describe such an extractor, which we have used successfully for over a year.
The extractor, the construction details of which are shown in Fig, 1, may be made of almost any metal, such as brass, iron, or stainless steel. We have used brass because of the ease of machining.
After centrifugation the extractor is inserted into the swinging bucket. Part F is stopped by the shoulder of the tube, thus preventing the extractor from entering the supernate. A counterclockwise twist of the knurled part B raises the taper T, expanding the arbor M against the 235