tracer. However, the isotope dilution aspect of 237Np analysis is fairly well detailed in the publication. spectrometry was rather lightly covered and the value of this powerful tool in radiochemical analysis might not be apparent to the novice reader. Wessman et al. Major et al. (1965) had reported on a method for determination of plutonium by tracer techniques in large biological samples. A cupferron-chloroform extraction was performed followed by anion exchange purification. The tracer was 236py and good yields, typically 55%, were obtained with tissue samples up to 5 kg in size. (1975) presented two purification/separation procedures, each of which utilized a sequential precipitation of Fe(OH)3, LaF3 La(0H)3; Dowex-l anion exchange colums and extraction with either tri-isooctylamine/xylene or thenoyltrifluoracetone/toluene extraction. Good yields and good separation from the actinides and fission products and activation products were obtained. For environmental samples of approximately 10-g ash, Wessman et al. (1977) report a rather simple ion exchange separation sufficient to obtain purification from the other transuraniums. Beta~emitting 239Np tracer is used for yielding. An 8 N nitric acid solution of the dissolved samples and tracers is treated to obtain Np (IV), Pu (1V), and U (IV), which are absorbed onto an anion exchange resin column of Dowex 1 x 4; Am and Cm and other impurities pass through. The Np, Pu, group is then eluted with 4 N HNO3-0.1 N HF and reabsorbed on similar but shorter columns. The column is washed with 8 N HNOg and HCl, then Pu is eluted with HC1-NH,I. The column is washed with HCl and then Np is eluted with 2 N HCl. Both Pu and Np are then ready for plating. PLUTONIUM PURIFICATION Chemical considerations for Pu analysis are very similar to those for Np. There are a wide number of procedures. Katz and Seaborg (1957) classify the methods roughly as precipitation, solvent extraction, and ion exchange processes. They further point out that all of these methods depend upon the fact that Pu (like U and Np) has a number of stable oxidation states and that the chemical properties of the element in one state may differ to a very considerable extent from those of the same element in a different oxidation state. Coleman's 1965-monograph on the Radiochemistry of Plutonium summarizes numerous purification steps for Pu along with comparable information on other elements. Coleman also screened "54 papers with procedures which were written in enough detail to do justice to the name." He included 19 radiochemical procedures and five special procedures in his collection. Only three are environmental procedures: one is for soil, vegetation, and water (TBP extraction); the second is for water, using chemisorption on CaF) followed by TTA extraction; and the third is the isolation of Pu in water on BiPQ, precipitates plus co-extraction with ferric cupferride. Seven of the procedures were for Pu in urine using ferric cupferride extraction; PrF3 precipitation and TTA extraction; LaF3 and TTA extraction; BiPO, precipitation, LaF3 precipitation and extraction into HDEHP; alkaline earth phosphate precipitation and anion exchange and extraction of primary amine from H2S0, solution. It is unfortunate that, at that late date, only five of the procedures dealt with isotope dilution analysis and none of the environmental urine analysis procedures were specifically designed for isotope dilution by alpha spectrometer analysis. Also, the entire subject of isotope dilution analysis using alpha Coleman (1965) commented that the anion exchange method is so simple and effective that it had become one of the standard laboratory methods for the separation of Pu. He noted that many examples existed of the use of anion exchange resins for Pu separations in HCl and HNO3 solutions. Even so, experience has shown that variations in the technique, sample matrix elements, the presence of other alpha emitters, and materials used markedly effect the recovery of the Pu and its radiochemical purity. A rather general approach on samples with ash or mineral content of 1 gram or greater is to isolate the Pu onto Dowex 1 x 4 from 8 N HNO3 solution. This may be done by pouring the solution of Pu (IV) through the column or the slurry-column technique of Kressin and Waterbury (1962). In the latter technique, about half the resin is added directly to the solution for bulk absorption and then combined, whereupon the resin is added back to the colum. Washes and elutions are performed as designated by the procedure being used. Many interfer~ ing ions are removed from the Pu by this column and the Pu is then eluted with 0.4 N HNO3-0.01 N HF. The same absorption and elution sequence is repeated with a smaller amount of resin and a smaller column, and the Pu is electroplated for counting. Examples of this type of procedure are given in the HASL Manual, Anonymous (1976, 19762), for 50-gram tissue samples and leaches of 100-gram soils. An alternate procedure, as given by Wessman et al. (1971), is to do the first column purification as in the HASL method. However, after loading the nitric acid solution directly onto the column, it is washed with hydrochloric acid solutions and the Pu ts eluted with HC1-NH,I. There are no significant advantages in this method over the HASL methods cited above; primarily, it is just another approach. For vegetation samples, Major et al. (1974) report using a single column of Dowex 1 x 4 and absorbing Pu from HCL solution. The column is then washed with 6 N HNO3 to remove interfering elements and then converted back to HCl form in order to elute Pu with HC1-NH,I. Of the 41 papers given at the 1975-USERDA-IAEA Symposium on Transuranium Nuclides in the Environment (Anonymous, 1976b), 11 papers listed Straight ion exchange procedures. Six other methods listed were TIOA extraction, TTA extraction and ion exchange, phosphate precipitation plus anion exchange and BaSO, precipitation. The methodology of analysis in the remaining papers was either not readily deduced, or was not germane to the subject. In the field of autopsy tissue analysis, Campbell et al. (1973) use anion exchange and Thomas et al. (1975) use a phosphate coprecipitation followed by anion exchange. Larson and Oldham (1974) have reported on a system using HBr and anion exchange for rapid selective Pu separation. 561