DISCUSSION An experiment was performed with a spike solution of 237pu, 241am, and 237Np to determine the activity distribution in the fat and filtrate portions. The results show less than 1% of the activity in the fat after the cold 6N HNO3 These results might be expected since the spike solution has not been wash. Four samples from an inhalation metabolism through metabolism mechanics. experiment for 24lam in tissues were analyzed to determine the 24lam content of the fat portion. method described. The sample was dissolved, filtered, and ashed by the The filtrate and fat portion were counted separately. The results are given in Table 1. In the four tests, the amount of 241am remaining in the fat portion ranged from 0.1 to 0.4% of the sample activity. For most applications, the small amount of 241!Am retained by the fat may be considered To date, in our laboratory, we negligible and the fat could be discarded. have adopted a conservative approach and processed all fat portions and combined them with the sample. To determine the ability to analyze the dissolved sample and recover the 24 1am activity, seven metabolism tissue samples containing 24lam were dissolved. The dissolved samples were assayed for **!am in a standardized jar counting geometry using a thin layer NaI (Tl) crystal as described by Major et al., (1974). Aliquots, ranging in size from 0.01% to 5.0% of the dissolved sample, were analyzed for 24am by the isotope dilution procedure previously reported (Major et at., 1974). Americium-243 tracer and alpha spectrometry are used. The results (Table 2) show satisfactory recovery of 241am from solution of various tissue types and activity levels, and there is no apparent bias within the limits of the procedures used. In summary, the described dissolution procedure for tissue samples using HF and HNO3 appears to be satisfactory for its intended purpose. Using this procedure, samples of 250 grams can be completely solubilized in less than an hour. The advantages of this procedure are: a. Equipment requirements such as charring and ashing furnaces and exhaust facilities are reduced. b. Ashing odors are reduced. c. Labor to tend ashing samples is reduced. d. Cost savings on laboratory ware and reagents is achieved. The procedure is expected to be adaptable to the analysis of large, low-level samples, such as autopsy samples. 280