ANALYTICAL BIOCHEMISTRY 71, 629 -631 (1976)

Chamber Seal for Condensation Free Loading and Unloading of Beckman Zonal Rotors

at Low Temperature

The use of zonal rotors in preparative ultracentrifuges generally necessitates prolonged operation of the centrifuge during loading and un- loading under open-chamber conditions. In the cases where maintenance of a low rotor temperature is desired, considerable moisture is condensed onto the cold surfaces of the refrigeration shell within the centrifuge chamber. This moisture has to be pumped out of the chamber before commencing high speed operation if good temperature control is to be maintained. The problems and possible results of operation at high speed with appreciable amounts of moisture within the chamber are described by Dobrota (1).

The "anti-condensation shield" supplied by Bechman Instruments for use with zonal rotors in their L series of preparative ultracentrifuges is essentially identical to that originally used by Anderson (2) and does not effectively prevent condensation buildup as claimed by the manu- facturer (3). Use of this shield during a loading operation at 5°C per- mitted a condensation buildup which required 7 hr of vacuum pump opera- tion to attain a pressure of less than 2 mm Hg within the centrifuge chamber. In addition to any problems associated with high speed operation at appreciable chamber pressures, this amount of moisture necessitates frequent servicing of vacuum pumps.

Any device to prevent this condensation must allow entry of the rotor feed and seal cooling lines and must be securely positioned in use but quickly removable on completion of loading.

We have designed and constructed in Lucite the chamber lid and gland assembly diagrammed in Fig. 1. Installation or removal of this device can be performed by one person in about 30 sec. (The chamber door stop on the top-right frame member must be removed and the centrifuge top removed or the access port enlarged to permit fitting of the Lucite lid). The loading seal is first installed in the rotor shield, the Lucite lid slid down the fluid lines, and the gland body is drawn into the tapered hole in the lid and secured by means of the gland nut. A water aspirator connected to one of the ports in the gland (not shown) is used to evacuate the chamber to give an internal pressure of about 60 mm Hg below ambient, with the result that the lid is secured by an effective force of about 200 lbs. Aspiration must be maintained as a slight

Copyright © 1976 by Academic Press, Inc. All rights of reproduction in any form reserved.

629

630 SHORT COMMUNICATIONS

# 0 rubber stopper

nut

~erO rmcj

age ceptor

FIG. 1. Schematic of Lucite lid and gland assembly. The gland detail is enlarged and only one fluid line portrayed for clarity. All cross-hatched items are of our manufacture.

leak of dry air into the chamber occurs via the existing venting valve. Removal of the lid is a reverse of the installation procedure.

Use of this lid makes loading at a constant temperature of 5°C feasible without any condensation occurring other than the small amount taking place between removing the loading seal and closing the chamber lid. Chamber evacuation times down to 20 min prior to accelerating to full speed are made possible.

Loading seal leakage is an additional source of moisture within the centrifuge chamber. To intercept this leakage we have installed a Lucite ring on the underside of the rotor shield. When this item is in use, the water aspirator line is connected to a stainless steel drain fitting on this ring and fluid collected is immediately withdrawn from the chamber.

CONSTRUCTION DETAI LS

The lid is machined from one piece of 1-in. Lucite sheet. A 30 ° taper hole is machined at the center to accommodate the gland body and the periphery is stepped to locate within the rim of the centrifuge chamber and rest on the existing O-ring. The gland assembly is produced from 3-in. diameter Lucite bar. A taper to match the lid taper is machined on the lower half of the body and the upper threaded portion is of a diameter to accommodate 6 tapered holes to fit No. 0 rubber stoppers. The fluid lines pass through 6 mm holes in these stoppers. The stopper holes were

SHORT COMMUNICATIONS 631

machined using a custom-made taper drill. The thread for attachment of the gland nut is 8 TPI, and the gland nut is serrated on the rim to afford good grip.

Dimensioned working drawings will be supplied upon request. Summary. The construction of a Lucite chamber seal for the Beckman

L series of preparative ultracentrifuges is described. Use of the seal during low temperature loading and unloading of zonal rotors eliminates water condensation on the rotor and refrigerated chamber shell; this in turn re- sults in a far shorter period of time being necessary to pump the chamber down to the low pressures required during the run to maintain low rotor temperature. In addition, the use of a Lucite ring attached to the underside of the Beckman rotor shield in conjunction with the chamber seal eliminates leakage from the loading seal as a source of chamber moisture during zonal operation.

ACKNOWLEDGMENTS

We are grateful to M. Symonds and W. Henderson of the Chemistry Mechanical Shop for their capable craftsmanship. Purchase of the Zonal Rotor and constituent parts was made possible by grants from the British Columbia Medical Research Foundation and the U.B.C. President's Committee on Research. The first author is a recipient of the Ogilvie Fellowship of the Chemical Institute of Canada. Operating grants trom the British Columbia Heart Foundation and the National Research Council of Canada to the second author are acknowledged.

REFERENCES

1. Dobrota, M. (1971) in Separations with Zonal Rotors (Reid, E., ed.), pp. Z - 2 . 5 - 2.6, University of Surrey.

2. Anderson, N. G., Waters, D. A., Fisher, W. D., Cline, G. B., Nunley, C. E., Elrod, L. H., and Rankin, C. T. (1967) Anal. Biochem. 21, 235-252.

3. Beckman Instruments publication L2-TB-059 Aug. 1968.

Department of Chemistry Laboratory of Chemical Biology University of British Columbia Vancouver, Canada V6 T-1 W5

Received November 14, 1975; accepted January 8, 1976

GEOFFREY WEBB

DONALD G . CLARK 1

1 Author to whom requests for reprints and working drawings should be addressed.