Simple Centrifugal Filtration Assembly for Preparation of Solid Samples for Radioassay Felix Bronner and Nils A. Jernberg, Rockefeller Institute for Medical Research, New York 2 1, N. Y.
devices a t present available for the urenaration of solid samples for radioassay ( 2 , 3) merely separate the precipitate from the supernate, which is then removed in a separate step. The described here (Figure 1) employs centrifugal forces for simultaneous separation and filtration and thus yields in one operation a precipitate ready for counting. CENTRIFCGAL
A
I
with the aid of tool G. Tightness of fit is further assured by the edge of the l o w x end Of A . This edge presses against the paper at an Of 20” The paper thus acts also as a gasket: The tapered end of A and the corresponding taper (80”) of the stainless steel planchet holder, C, facilitate removal of the filter Daper \Then the apparatus is taken ap& with the aid bf device TI.
er’s earth suspension. [Ten grams of Florida fuller’s earth (Floridin Co., Karren, Pa., 60-100 mesh) is suspended in 1000 ml. of distilled water and filtered through glass wool; 1.5 mi. of filtrate is used per circle of filter paper. 1 Centrifugation follows for 5 minutes a t 150 to 175 g’s. The use of centrifugal force in ewess of 175 g’s may yield a cloudy filtrate. If the filtrate is cloudy, it is reprocessed. After centrifugation, the locknut is removed and the inside assembly is pushed out with the aid of H . The filter paper is then transferred to a holder for counting. Samples with a volume in excess of the 15-ml. capacity of the upper chamber, A . can be prepared by successive centrifugation. Before the thin layer of precipitate is counted, it is coated n-ith 4 drops of collodion (0.5yoin acetone). This keeps the samples from flaking and makes it possible to store them longer. Ordinary washing after use has kept the apparatus free from contamination. RESULTS
A series of duplicate ssmples was prepared b y both suction and centrifugal filtration. Difference.; in the counts obtained on duplicate samples were not statistically significant, and the tlyo methods are therefore comparable. I n a fuither test. R standard prepared by suction filtration counted 1163 counts per minute [standard deviation 24, six samples), while the same standard prepared by centrifugal filtration counted 1179 (standard deviation 37, four samples). The apparatus also has been used successfully for the isolation of sulfur3Llabeled barium sulfate precipitates.
Diagonal shading: Stainless steel Cross-hatching: aluminum
The use of centrifugal filtration not only permits the easy handling of many samples a t once (up to 16 samples in a conventional centrifuge equipped with a 16-place head), but also speeds operation in those cases where suction filtration (4) would normally be very slow (as when calcium oxalate is precipitated from serum which has not previously been deproteinized). A t the same time it minimizes the danger of losing some precipitate in siphoning off the supernate, as may easily occur in existing centrifugal devices. CONSTRUCTION DETAILS
The apparatus (Figure 1) consists 01 a polished, stainless steel filter tube in two parts, A and B, between which a porous planchet holder, C,and a circle of filter paper, D,are held. The filter tube rests inside a polished aluminum carrier, E, where i t is kept tightly in place b y a stainless steel locknut, F , screwed in 462
ANALYTICAL CHEMISTRY
The apparatus can be constructed from commercially available materials a t a n approximate cost of $60. Tolerances of the filter tube and planchet holder were held a t 1 0 . 0 0 3 inch. The porous metal of the planchet holder is available as porous stainless steel sheets, composition 18-8, Type 304 (Micro Metallic Corp., Glen Cove. S . Y.; 3 / 3 2 inch thick. mean pore opening, 10 microns). PROCEDURE
The apparatus has been used in this laboratory for the preparation of calcium-45-labeled calcium oxalate samples. After overnight precipitation ( I ) , the samples are transferred quantitatively to the centrifugal filtration assembly. Before transfer the filter paper (Schleicher and Schuell, No. 589, red ribbon, 80-mm. diameter) is prepared with full-
LITERATURE CITED
(1) Bronner, F., Harris, R . 8., llaletskos, C. J., Benda, C. E., J . .\-idtition 54,
523 (1954). (2) Calvin, l f . , Heidellmger, C., Reid, J. C., Tolbert, B. ll.,Tankn-ich, P. F., L‘Isotopic Carbon. Techniques in Its lleasurement and Chemical Manipulation,” pp. 11421, Wiley, A-cw Tork, 1949. (3) Comar, C. L . , “Radioisotopes in Biology and Agriculture. Principles and Practice,” pp. 1iO-1, \IcGrawHill, Yew York, 1955. (4) Henriques, F. C., J r . , IGstiakowski, G. B., llargnetti, C., Schneider,
IT. G., IXD.ESG. CHEII., .IY.+L. ED. 18, 349 (1946). WORK carried out during the tenure by Felix Bronner of a research fellowship of the Arthritis and Rheumatism Foundation, supplemented by a grant from the Helen Hay \T’hitney Foundation. This aid is gratefully acknonledged.
