US 3487994 A
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Description (OCR text may contain errors)
Jan. 6, 1970 D. H. MOORE 3,4 7,994
ANALYTICAL ULTRACENTRIFUGE CELL Original Filed Aug. 24, 1967 I0 I? No.
United States Patent O 3,487,994 ANALYTICAL ULTRACENTRIFUGE CELL Dan H. Moore, Cherry Hill, N.J., assignor to Canal Industrial Corporation, a corporation of Maryland Continuation of application Ser. No. 663,150, Aug. 24, 1967. This application May 8, 1968, Ser. No. 727,752 Int. Cl. B04b 9/12, 9/14 US. Cl. 233-26 4 Claims ABSTRACT OF THE DISCLOSURE An ultracentrifuge rotor assembly comprises a rotatable centrifuge head in which are mounted a plurality of bucket-type specimen analytical cells with transparent windows each having a specimen-containing cavity and a plurality of transversely extending shoulders symmetrically disposed about the axis of the cell. Each of the cells is supported in the head by a resilient pin and the head has a plurality of supporting sockets each disposed to be engaged by the shoulders of one of the cells and to support it radially during normal operation. The flexible supporting pin is deflected during normal operation by the centrifugal force acting on the pin and, when the ultracentrifuge is stopped for removal of the cell, the pin retracts it from the head socket and permits it to swing into a vertical position for removal. The analytical cell comprises an integral metal body having a specimenreceiving cavity and connecting recesses of larger areas in the upper and lower faces thereof and a transparent window secured by an epoxy resin adhesive in each of the recesses to form a single unitary structure. The vertical walls of the cell cavity lie substantially in radial planes during normal operation of the cell and the cell body has a plurality of transversely extending shoulders symmetrically disposed about the axis. a
RELATED APPLICATION This application is a continuation of applicants prior application Ser. No. 663,150, filed Aug. 24, 1967, now abandoned.
BACKGROUND OF THE INVENTION Ultracentrifugation can be divided into two main categories:
Preparative ultracentrifugation generally makes use of one or the other of two types of rotating heads:
1) Angle-in which the specimen cells are tubular and make a fixed angle with the axis of rotation.
(2) Swinging bucket-4n which the specimen cells are tubes which hang vertically when the rotor head is at rest and swing out horizontally when the head reaches operating speed.
Such tubular cells of both the angle and swinging bucket types generally have a relatively large volume capacity, of the order of 15 to 200 cc. but, because of the centrifugal stresses on the angle cell or on the pivotal support of the swinging bucket, heads including large cells generally must be operated at relatively lower centrifugal fields.
Preparative ultracentrifugation is used to separate colloidal substances with different densities or frictional coefficients for further analysis or examination. This separation may be made in solvents of uniform density or in solutions with a gradient in density from top to bottom. Gradient centrifugation is better served by swinging bucket rotor heads.
At present, preparative operations are carried out in the dark since the operator is not able to determine what is taking place in the sample tube until the centrifuge is stopped and the specimen cell removed. During this manipulation, the distribution of components in the cell may be altered. Also, centri'fugation may have been too short or too long to give a desired distribution or separation.
Analytical ultracentrifugation, on the other hand, requires special cells with radial walls to prevent convection and transparent windows and an optical system for viewing and photographing the contents of the cell while the head is rotating. Heretofore, analytical cells have always been fixed in the rotating head with the top toward the axis of rotation and the bottom toward the periphery. Usually, such cells have a low volume capacity, less than 1 cc., and have involved a complex construction consisting of many parts which must be taken apart for cleaning after each use and reassembled and reinstalled in the head for subsequent use. Such cells have the disadvantage that it is generally necessary to install them in the head and remove them from the head in a horizontal position which permits a certain amount of mixing of the cell contents both before and after centrifugation.
For a more detailed discussion of various ultracentrifugation processes and of standard equipments available, see the article Centrifugation by applicant in Medical Physics, Vol. II, Otto Glasser, Editor, Year Book Publishers, Inc., Chicago, 1950, pp. 172-183.
It is an object of the invention, therefore, to provide a new and improved rotor assembly for an ultracentrifuge capable of use for either preparative or analytical ultracentrifugation, combining the above-described advantages of both types.
SUMMARY OF THE INVENTION In accordance with the invention, there is provided a swinging bucket-type analytical ultracentrifuge cell which comprises an integral metal body having a specimenreceiving cavity and connecting recesses of larger areas in the upper and lower faces thereof and a transparent window secured in each of such recesses to form a single unitary structure.
For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, while its scope will be pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWING Referring to the drawing:
FIG. 1 is a perspective view of an ultracentrifuge head embodying the invention, at rest;
FIG. 2 is a fragmentary cross-sectional view of a head showing a specimen cell substantially in the position occupied during normal operation, while FIG. 3 is a side elevation of the specimen cell shown in FIGS. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION Referring now more specifically to the drawing, there is shown a rotor assembly for an ultracentrifuge comprising a rotatable supporting ultracentrifuge head 10. The supporting and driving mechanism for the head comprises no part of the present invention and is, therefore, not shown. It may, for example, be of the type described and claimed in the copending application of applicant and John U. White, Ser. No. 480,407, filed Aug. 17, 1965, and assigned to the same .assignee as the present application. The rotor assembly also includes a plurality of bucket-type specimen cells 11, each of which, as
shown more clearly in FIG. 2, has a specimen-containing cavity 12 and a circular transversely extending shoulder 11a, 11a or a plurality of individual shoulders symmetrically disposed about the longitudinal axis of the cell 11.
As shown more clearly in FIG. 2, the vertical walls of each of the cell cavities lie substantially in radial planes of the rotor head during normal operation when centrifugal force swings the bucket-type cells outwardly into a substantially horizontal positon. The upper and lower walls of each of the cell cavities 12 is in the form of a transparent window, such as the windows 13 and 14 cemented into cavities in the upper and lower faces of the cell 11 with a suitable adhesive such as an epoxy resin. The term transparent, as applied to the windows 13 and 14, is used to indicate that they have a high transmissivity to electromagnetic radiation in that portion of the spectrum used for analyzing the contents of an ultracentrifuge cell, specifically including any desired portion or all of the range from infrared to ultraviolet, depending upon the application. Before the windows 13, 14 are cemented into place, the metal parts are preferably anodized or otherwise suitably treated or coated to prevent chemical reaction with the fluids under study. A resilient pin 15 supports each of the cells 11 from the head, for example, the pin passes through extending lugs 11b, 11b of the cell and through an oversize hole 16a in a lug 16 projecting from the frame of the head into a socket 17. The pin 15 may be retained in place in any suitable fashion. As shown, the pin 15 extends through the walls of the socket 17, being threaded into one wall thereof. The cell 11 is provided with a hole 18 through its upper wall for filling the cavity 12 and extracting the specimen therefrom. This hole is closed by a screw plug 19 and a sealing gasket 20. The hole 18 is preferably relatively large to permit easy access to the inside of the cell for cleaning.
The head is formed with a plurality of supporting sockets, such as the socket 17, in which the upper ends of the cells 11 are disposed when the head is at rest and each having surfaces disposed to be engaged by the shoulders of one of the cells 11 and to support the same radially during normal operation upon deflection of its associated pivot pin by centrifugal force acting upon the cell. Specifically referring to FIG. 2, the shoulders 11a, 11a of the cell 11, during normal operation, are forced to the right until they engage the surfaces 17a, 17a of the socket 17, although these abutting surfaces are shown slightly separated in the drawing for the sake of clarity.
It is believed that the operation of the ultracentrifuge rotor assembly will be apparent from the foregoing description. In brief, when the rotor head is at rest, the cells 11 all swing vertically downwardly about their respective pivot pins 15, as shown in FIG. 1. As the rotor head is brought up to speed, the specimen cells 11 swing upwardly into the horizontal position, as shown in FIG. 2, and, at normal operating speed, the centrifugal force acting on the cells is sufiicient to force them outwardly up to speed and after it reaches its final operating speed. During this period, the sedimentation of a-colloid in a density gradient in a cell 11 can be observed while the redistribution is actually taking place. Such observations are important, both practically and theoretically. Furthermore, absorption, Schlieren, interference, or other optical systems can be used to observe or record the distribution of components at all times during the centrifugation process. At the end of a run, the resilient pin 15 retracts the cell 11 from engagement with the surfaces 17a, 17a of the head socket and the cell gently and gradually swings to the vertical position so that the separated fractions of the specimen in the cell can be removed undisturbed for further study. 1
This cell can also be used' for makinga synthetic boundary as described by G. Kegeles (Jour. Amer. Chem. Soc. 74:5532, 1952) and by E. G. Pickels et al. (Proc. Nat. Acad. Sci. U.S. 381943, 1952) and by Vinograd et al. (Proc. Nat. Acad. Sci. U.S. 49:902, 1963). However, with the type of analytical cell embodied in the present invention, most layers can be prepared before the cell is connected to the rotor head because both gravity and centrifugal force is always directed toward the bottom of the cell as a result of its free swinging action. This cell, although constructed of very few pieces, can be shaped to accommodate most of the processes accommodated by previous analytical cells, such as the long radial length double-channel cell of H. K. Schachman (Ultracentrifugation in Biochemistry, pp. 178-180, Academic Press, New York, 1959).
Thus, the ultracentrifuge rotor assembly embodying the invention is useful both for preparative or analytical processes and the rotor head 10 can be made much lighter than in the case of a rotor head including a fixed standard analytical cell. This is because the cell constitutes the greatest radius of the rotating head assembly. In the case of a. head with a fixed analytical cell, the body of the head must extend considerably beyond and around the cell to support the very great centrifugal forces on the cell, thus significantly increasing its size and weight and the centrifugal forces which it must withstand.
What is claimed is:
1. A swinging bucket-type analytical ultracentrifuge cell comprising 'an integral metal body having a specimen-receiving cavity and connecting recesses of larger areas in the upper and lower faces thereof and a transparent window secured in each of said recesses to form a single unitary structure.
2. An ultracentrifuge cell in accordance with claim 1 in which said windows are secured in said recesses by an epoxy resin adhesive.
3. An ultracentrifuge cell in accordance with claim 1 in which the vertical walls of said cell cavity lie substantially in radial planes during normal operation of the cell.
4. An ultracentrifuge cell in accordance with claim 1 in which the cell body has a plurality of transversely extending shoulders symmetrically disposed about its' axis.
HENRY T. KLINKSIEK, Primary Examiner