plutonium was rerr.oved by selective solvent extraction and the remaining solution analyzed spectrographically. The entire chemical operation was performed in the original beaker, so that no trace elements were lost other than those mentioned’above. ANALYSISOF UF,. When UFI was fused with NH4HB04at a low temperature in platinum, the fluoride was quickly eliminated and the uranium oxidized. Evaporation of the bisulfate left an easily soluble uranyl sulfate. This was dissolved, the uranium extracted, and the aqueous layer analyzed spectrographically. DISSOLUTIONOF METALSWITHOUT HF. Hydrofluoric acid is necessary to dissolve some metals. The con-
tinued presence of the fluoride ion is sometimes undesirable after the dissolution, but this ion is often difficult to eliminate without some serious disadvantage to subsequent operations. This situation arose, for example, in the determination of trace impurities in niobium-rare earth alloys. The use of H F would have given insoluble rare earth fluorides; the fluoride would then have been diffcult to eliminate without rendering the niobium insoluble, losing trace elements, or both. These alloys dissolved with little difficulty in molten NHJISOI. In this case, however, immediate evaporation of the bisulfate would have left an insoluble residue. The melt was therefore dissolved and the major con-
stituents were precipitated with gaseous NHa, centrifuged, and redissolved in concentrated HCl or oxalic-nitric acid mixture. The supernate, containing the bisulfate and the impurities soluble in ammonium hydroxide solution, was treated with excess sulfuric acid and evaporated to remove the ammonium salts, and the two portions then were recombined. This reagent should be especjally valuable where subsequent determination, spectrographic, colorimetric, or electrochemical, would be hampered by the presence of gram quantities of fusion agent. PITTSBURGHConference on Analyticai Chemistr and Applied Spectroscopy, PittsburgK, Pa., March 3, 1960.
A Simple, Wet Oxidation Procedure for Biological Materials 1. 1. Reitz, W: H. Smith, and M. P. Plumlee, Animal Science Department, Purdue University, West Lafayette, ind.
of plant or animal W matter for subsequent mineral analyses is superior to dry ashing in ET OXIDATION
many respects. In an excellent review article Middleton and Stuckey (3) point out that in dry ashing there is the possibility that certain elements might be absorbed or combined with other ash constituents or even with the material of the crucible, and that contamination by dust might occur. A large number of wet oxidation procedures using some combination of nitric, sulfuric, or perchloric acids have been reported in the literature. However, many af these methods are time consuming and require special equipment and careful attention by the operator to be effective and safe. Although perchloric acid is an effective aid to digestion, its introduction in large quantities is potentially dangerous as it can react with explosive violence under certain conditions. The method described for wet oxidation using nitric, sulfuric, and a small amount of perchloric acid requires very little attention by the operator and no specialized equipment. Perchloric acid is added dropwise near the end of the oxidative process. In this respect the method is similar to that used by Gettler and Bastian ( 2 ) for the preparation of tissue or blood for zinc analysis, and to that of Feldstein and Klendshoj (1) in preparing tissue samples for mineral analysis in toxicology studies. However, all these workers used Kjeldahl flasks in which to carry out the oxidations. PROCEDURE
All the quantities mentioned in the
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ANALYTICAL CHEMISTRY
subsequent directions are for samples of approximately 5 grams, dry weight. For other quantities the proportions should be altered accordingly. Weigh the sample accurately into a 250-ml. Erlenmeyer flask and add 35 ml. of codcentrated nitric acid. All the acid a n be added a t once unless the sample is such that it foams badly on the addition of the acid. I n this case, add only about 5 ml. of acid; allow this to react before adding the remainder. Set the flask on a hot p h t e using the lowest temperature setting in a hood to digest very slowly for about 4 to 6 hours. At this stage of the digestion, the solution is a clear yellow and the initial volume is not markedly reduced. Cool the sample overnight, whereupon any fat that is present solidifies. If there is a significant amount, carefully filter it off by pouring the sample through a thin layer of glass wool in a stemless funnel. Return the clear filtrate to the Erlenmeyer and wash the glass wool several times with a small amount of concentrated nitric acid. Add 2 ml. of concentrated sulfuric acid and return the flask to the hot phte to heat rapidly. If the sample has a tendency to lLbump”or splatter during this step, lower the heat and cover the flask with a stemless funnel until the sample boils smoothly. The sample needs no careful watching until the volume is well reduced and a frothing action sets in. Charring a p pears rather suddenly. If a number of samples are being run simultaneously, the charred sample can be removed from the heat a t this point and the oxidation completed a t a later time if desired. To the hot charred sample carefully add dropwise a digestion mixture consisting of two parts of 72% perchloric acid and one part of concentrated nitric acid. By adding the. perchloric acid
dropwise, the danger of violent explosion is eliminated and the material is oxidized quickly and completely About 5 minutes are required for this step. The color of the mixture gradually turns from black to brown to colorless as the digestion mixture is added and heating is continued. Only 0.5 to 3.0 ml. of the digestion mixture are necessary to clear the material. When the sample is clear, heat it strongly at the fuming stage for an additional 10 to 15 minutes. Only the white or slightly yellow mineral residue and a small amount of sulfuric acid are left in the flask. Remove the sample from the heat, cool, and add about 10 ml. of distilled water and 3.0 ml. of concentrated hydrochloric acid. Boil the contents gently to accomplish solution and then pour into a volumetric flask of appropriate size. A blank on the reagents can be prepared by evaporating the same quantity of the acids as used in the unknown. For very accurate mineral work it is advisable to use redistilled acids. Directions for this redistillation have been described ( 4 ) . Samples of various feedstuffs, animal tissue, and milk have been oxidized successfully and subsequently analyzed for calcium, phosphorus, iron, and zinc using the described method of oxidation. The procedure appears suitable for a wide spectrum of trace mineral analyses, and hence would be a helpful tool for many laboratories carrying on this type of investigation. LITERATURE CITED
(1) Feldstein, M., Klendshoj, N. C., Analyst 78,43-7 11953). ( 2 ) Gettler, A. O., Bastian, R., Am. J . Clin. Pathol. 17,244-9 f1947). (3) Middleton, G., Stuckey, R. E., Analyst 78,53242 (1953). (4) Piper, C. S., “Soil and Plant Analysis,” p. 306, Interscience, New York, 1944.
