Analyst, April, 1968, Vol. 93, pp. 235-236 235 Loss of Polonium-210 on Dry Ashing Rat Tissues in a Muffle Furnace BY J. J. CLEARY AND E. I. HAMILTON (Radiological Protection Service, Clifton Avenue, Belmont, Sutton, Surrey) The losses of polonium-210 during dry ashing of rat tissues are reported, and it is shown that losses occur at lower temperatures than generally referred to in the literature. DURING the dry ashing of biological samples in a furnace some elements are partially or completely lost. In some circumstances losses can be prevented by careful wet ashing of the sample at about 80" C . Radiotracer techniques are convenient when investigating losses of elements during ashing procedures, although those techniques, in which a radioisotope of the element is added to a sample, in vitro, are not satisfactory if the radioisotope is not of the same chemical form as the element being assayed.In the work reported here, losses of polonium-210 during the ashing of biological samples were investigated for polonium-210 that was previously incorporated into the animal tissues by injection in vivo. In a previous paper1 this approach was described for the loss of some selected elements from rat tissues after dry ashing in silica crucibles. Apart from volatilisation losses, some elements adhere to the internal surfaces of the dishes, as a result either of adsorption or chemical reaction. In the present work these losses were not considered separately from the volatilisation losses. Male hybrid rats, injected intraperitoneally with 25 microcuries of polonium-210 in 0.25 M hydrochloric acid, were killed after 4 hours. The kidney and femur were removed, and the marrow in the femur extracted by washing with water.Samples were then divided into two, one portion being used for dry ashing and the other as a control from which polonium was extracted after wet ashing. The loss of polonium as a result of wet ashing seems unlikely and has not been reported in the l i t e r a t ~ r e . ~ , ~ , ~ ~ ~ , ~ ~ ~ TABLE I LOSS OF POLONIUM-210 ON DRY ASHING RAT KIDNEY AND FEMUR IN A MUFFLE FURNACE Heating temperature O C 200 300 400 600 600 700 900 Loss from kidney, per cent. 40 63 78 87 94 97 100 Loss from femur, per cent. N O 39 79 93 96 96 -100 The samples for dry ashing were heated in the furnace for 16 hours at the selected temperatures, and any residue dissolved by the wet-ashing procedure* used for the control samples.After both the ashed samples and control specimens had been dissolved to give a clear solution, the chemical yield from subsequent processes was monitored by the addition of polonium-208 as a tracer. The polonium in the sample solutions was separated, by spontaneous deposition, on to clean nickel discs, and the activity from polonium-208 and236 CLEARY AND HAMILTON polonium-210 determined by a-spectrometry with a gold-plated surface barrier detector under vacuum. The over-all error on plating and counting was +15 per cent. The results of our measurements are given in Table I, in which the activity of polonium-210 lost after dry ashing is expressed as a percentage of that found in an equal weight of tissue subjected to the wet-ashing procedures, for which no losses are expected.The results show that while some polonium is lost when dry ashing at temperatures in excess of 100" C, virtually all of the polonium is lost above 800" C. Several references in the l i t e r a t ~ r e ~ , ~ v * ~ ~ ~ ~ suggest that polonium is lost between 425" and 600" C; this work shows that considerable loss occurs below 425" C. The greater loss of polonium-210 in kidney, compared with femur, at low temperatures is possibly a reflection of differences in chemical binding of the polonium. REFERENCES 1. Hamilton, E. I., Minski, M. J., and Cleary, J. J., Analyst, 1967, 92, 267. 2. Holtzman, R. B., Hlth Phys., 1963, 9, 386. 3. Minto, W. L., in Fink, R. M., Editor, "Biological Studies with Polonium, Radium and Plutonium," 4. Holtzman, R. B., and Ilcewicz, F. H., Science, 1966, 153, 1269. 6. Ferri, E. S., and Baratta, E. J., "Radiological Health Data and Reports," U.S. Department of 6. Blanchard, R. L., Analyt. Chem., 1966, 38, 189. 7. Figgins, P. E., "The Radiochemistry of Polonium,'' National Academy of Sciences, Washington, 8. Jeffrey, H., Olubajo, F. O., and Jewell, W. R., Analyt. Chew., 1960, 32, 306. McGraw-Hill Book Co., New York, 1960, p. 16. Health, Education and Welfare, Volume 7, No. 9, 1966, p. 486. D.C., NAS-NS, No. 3037, 1961. Received August 24th, 1967