R. B. Grieves, W. Charewicz,and P. J. W. The, Sep. Sci., I O , 77 (1975). R. B. Grieves, R. L. Drahushuk,W. Walkowiak, and D. Bhattacharyya,Sep. Sci., in press. W. Walkowiak and R. B. Grieves, J. lnorg. Nucl. Chem., in press. , R. B. Grieves, Chem. Eng. J. (Lausanne),9, 93 (1975). (10)C. Jacobelli-Turi, S.Terenzi, and M. Palmera, ind. Eng. Chem., Process I
Des. Dev., 6,163 (1967). (11) C. Jacobelli-Turi, S. Terenzi, and M. Palmera, lnd. Eng. Chem., Process Des. Dev., 6,161 (1967). (12)J. A. Lusher and F. Sebba, J. Appi. Chem. Biotechnol., 15,577(1965);16, 129 (1966).
(13)8. L. Karger, R. P. Poncha, and M. M. Miller, Anal. Lett., 1, 437 (1968). (14)B. L. Karger and M. M. Miller, Anal. Chim. Acta, 48,273 (1969). (15) W. Charewicz and J. Niemiec, Nukleonika, 14, 17 (1969). (16)"Stability Constants", Spec. Pub/. No. 17, The Chemical Society,London, 1964. (17)K. A. Kraus and F. Nelson, Proc. First lnt. Conf. Peaceful Uses At. Energy, Geneva, 7, 113 (1956).
RECEIVEDfor review October 20, 1975. Accepted February 18, 1976.
Solvent-Solvent Extraction of Rhodium- 103m from Ruthenium103 Employing a Sulfate-Carbon Tetrachloride Medium Claude E. Epperson,' Robert R. Landolt," and Wayne V. Kessler Bionucleonics Department, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, Ind. 47907
103mRhin equilibrium with parent lo3Ruwas separated in yields of 94% of those theoretically possible. lo3Ruchloride was first converted to the tetroxide which was then extracted from an aqueous solution of the equilibrium mixture with carbon tetrachloride.
Large quantities of 1°3Ru are available in nuclear fuel wastes. This radionuclide with a half-life of 39.8 days decays to loBmRh(tlj2 = 57 min). Some uses have already been found for 103mRhin the field of nuclear medicine ( I ) and, if this nuclide were readily available, additional uses would undoubtedly be found. Furthermore, the decay of IoBmRhleads to stable rhodium, an important metal. Estimates (2) indicate that the annual yield of rhodium from nuclear fuel wastes may equal the consumption level. Consequently, a practical method for separating loBmRh,either alone or in combination with stable Io3Rh,from the stable and radioactive ruthenium isotopes present in nuclear fuel wastes would be desirable. A survey of the literature revealed that no satisfactory, fast, and simple radiochemical separation of loBmRhfrom lo3Ruhas been reported. Ion exchange separations have been generally unsatisfactory (3-5), because of considerable amounts of Io3Ru contamination. .Extensive column chromatography studies in the authors' laboratory have produced similar unsatisfactory results. Published reports devoted solely to the separation of stable rhodium from ruthenium are few in number (6-9). Almost invariably, ruthenium is separated from other platinum metals by distilling off ruthenium as the volatile R u 0 4 from concentrated perchloric acid or another oxidizing material. Although many of the separations are ingenious, the time required to complete them is lengthy considering the short half-life of IoBmRh.In addition, the separations are usually nonrepetitive and tend to leave the separated rhodium in a form too complicated for immediate usage. In some instances, Ru04 has been separated from other platinum metals using solvent extraction techniques. The determination of submicrogram quantities of ruthenium (10) and purification of milligram quantities of ruthenium and rhodium (11,12)have utilized this method. These techniques (10-12) have been adapted and modified for this study. The basic separatory procedure is: 1) fume (evaporate) a Present address, College of Pharmacy, University of Arkansas for Medical Sciences, Little Rock, Ark.
sample of Io3Ruchloride in equilibrium with the chlorides of loBmRhand Io3Rh in 1:l sulfuric acid for a period of time to convert Io3Ruto its sulfate form and to remove chloride, 2) add ceric sulfate in sulfuric acid to convert Io3Rusulfate to Io3Ru tetroxide, 3) remove Io3Ru tetroxide from the aqueous acid phase by extracting it into carbon tetrachloride, 4) recover the aqueous acid phase containing loBmRhwhich is not extractable in carbon tetrachloride, and 5) recover Io3Ru for later reuse from the organic phase with an aqueous.reducing extraction.
EXPERIMENTAL Apparatus. Radioactivity measurements were made with a sodium iodide well crystal and a multichannel analyzer. Reagents. Ceric Sulfate Reagent. A 0.2 N solution was prepared by dissolving ceric ammonium sulfate dihydrate (G. Frederick Smith) in 2 M H2SO4. This solution was allowed to stand undisturbed for 2 weeks and was then filtered through a fine grade sintered glass filter. Carbon Tetrachloride. SpectrAR (Mallinckrodt) was used as the organic extractant. Radioactiue Ruthenium. lo3Ru in equilibrium with loSmRhwas obtained from Amersham/Searle as ruthenium trichloride in 3 N HCl. The specific activity was approximately 5 mCi/mg of ruthenium. A stock solution was prepared to contain about 10 fig (50 fiCi)/ml in 2 N HC1. The radionuclidic purity was determined by y-ray spectrometry and half-life verification. Extraction Procedure. A 100-filaliquot ( 5 pCi) of the stock solution was added to 5 ml of 1:l HzS04 in a 20-ml glass beaker. The beaker was heated at a medium heat on a hot plate until white sulfuric anhydride fumes appeared. Heating was continued for 80 min following onset of the white fumes. The beaker was then cooled to room temperature and evaporation losses were replaced with water to make 5 ml of solution. Five milliliters of ceric sulfate reagent was added and the beaker was covered with a watch glass and allowed to stand for 10 min. The contents were then poured into 10 ml of carbon tetrachloride contained in a 60-ml separatory funnel equipped with a Teflon stopcock and a ground glass stopper. Three 1-min carbon tetrachloride extractions of 10 ml each were performed. The carbon tetrachloride extracts were combined and stored for subsequent recovery of Io3Ru if desired. An aliquot of the aqueous phase containing the loBmRhwas removed by pipet, placed in a plastic vial, and assayed immediately for IoBmRhand Io3Rucontent by y-ray spectrometry. For accurate determination of the 10BmRhyield, the elapsed time from separation to assay was considered by measuring from the start of the first extraction to the beginning of the assay. Reclamation of Extracted lo3Ru.To determine if reclaimed lo3Ru could be reused, the carbon tetrachloride extracts (30 ml) were added to 10 ml of 2 M HzS04 containing 1mg of sodium sulfite in a separatory funnel. The two phases were shaken for 90 min on a wrist action shaker. The organic phase was then found to be entirely free of radioactivity. After aging the aqueous phase overnight to allow loBmRh ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
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to attain equilibrium with lo3Ru,it was adjusted to a 1:1 H2S04solution with concentrated HzS04. Starting with the fuming step, a 5-ml aliquot was carried through the extraction procedure. Storage of Fumed lo3Ru.To determine whether lo3Rucould be fumed and then stored for extended periods of time without affecting subsequent extractions, samples, with and without carrier (RuC13, M), were fumed. These were stored at room temperature for 38 days and were then extracted starting with the ceric sulfate oxidation step.
Fumed and stored 38 days with Ru carrier Fumed and stored 38 days without Ru carrier
loBrnRhyield
lo3Rucontamination
80 f 2
2.1 =k 0.5
78 i 3
2.0 i 0.4
RESULTS AND DISCUSSION Each extracted sample was evaluated by y-ray spectrometry. The 20-keV x ray of 103mRhand the 498-keV y ray of Io3Ru were used in determining their respective concentrations in a sample. Two counts were made on each sample. First, using a high amplifier gain, the spectrum of the loBmRh x ray was obtained. The x ray appeared as a peak superimposed on a broad flat continuum of Compton counts generated by lo3Ruy rays. The net loBrnRhx-ray count was obtained by using a standard spectrum stripping technique to remove Compton counts under the x-ray peak. Then, using a lower amplifier gain, the y-ray spectrum of Io3Ruwas obtained. The total area under the 498-keV y-ray photopeak was integrated to obtain the lo3Ru count. Before integration, background counts were stripped from each spectrum. The two criteria used to evaluate the efficiency of extraction were the yield and the radionuclidic purity of each freshly separated loBmRhsolution. Samples of 103R~-103mRh were always aged enough to be in equilibrium prior to extraction. Following an extraction, a 5-ml aliquot of the aqueous phase was immediately assayed for its loBmRhand lo3Ru content. The radioactivity levels of all samples were sufficient to produce a t least 10 000 net counts in a 1-min counting period, thereby yielding a counting error not greater than 1%.A 5-ml reference sample of equilibrium 103R~-103mRhwas also counted in each assay. The efficiency of an extraction was determined by comparing the loBmRhand Io3Ru activities initially available for separation with the activities actually separated by the extraction. Unless otherwise indicated, the experimental results quoted are the mean and the standard deviation expressed as percentages of six replications of each experiment. The loBrnRh yield is the percentage of the initial 103mRhwhich remained in the aqueous phase after extraction. Ruthenium-103 contamination is the percentage of the initial Io3Ru remaining in the aqueous phase after extraction. The results of the extraction procedure were: loBmRh yield
Io3Rucontamination
94 i 0.6
3.8 =k 0.7
The experiment to determine if previously extracted lo3Ru could be successfully reused was performed on the carbon tetrachloride extracts. The results were: loBmRh yield
Io3Rucontamination
90
2.4
I t was found that all the lo3Rucontained in the carbon tetrachloride phase could be reclaimed in a small volume of 2 M sulfuric acid. I t is evident that extracted Io3Ru could be used again. This makes a cyclic extraction system possible whereby lo3Ru can be recovered repeatedly, thereby producing a “generator” system for the production of loBmRh. The results of the experiment on fumed and stored samples were: 980
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These results indicate that samples may be fumed when convenient, then stored for separation a t a later time. The availability of samples ready for immediate oxidation and extraction reduces the required separation time from over 2 h to approximately 15 min. Also, Ru or Rh carrier is not required to maintain long term stability of the sulfate form. Because of the highly reactive nature of Ru04, all components of the separatory system were given special consideration. Considerable care was exercised to exclude all traces of dust, paper, organic materials, organic vapors, and hydrochloric acid vapors from contact with reagents or glassware. All containment vessels were glass. The use of stopcock grease or protective silicone coatings must be avoided. They were found to cause the reduction of considerable quantities of R u 0 4 to a nonextractable species. I t was necessary to use dilute sulfuric acid as a glass lubricant. Glassware must be scrupulously cleaned. Routine washing of glassware was insufficient to prevent significant glass wall adsorption of Io3Ru.Removal of the adsorbed lo3Ruwas found to be extremely difficult. Micro (International Products Corp.) glass cleaner was used to clean all glassware in this study. After cleaning, all containers were wet with dilute sulfuric acid and allowed to drain. Glassware rinsed with sulfuric acid adsorbed much less Io3Ru and the adsorbed Io3Ru was much easier to remove. In separatory funnels cleaned in this way, phases separated very cleanly and rapidly with no droplets adhering to the side walls. All reagents must be of high purity. After aging several days, the ceric reagent was found to contain a small amount of a very fine white precipitate. I t was reported (13)that ceric ammonium salts usually contain traces of phosphate which give rise to a slow precipitation of ceric phosphate on standing. Therefore, this reagent was allowed to stand undisturbed for a t least 2 weeks after preparation. The solution was then filtered through a fine grade sintered glass filter. This solution was crystal clear and remained stable for many months, and no further precipitation was evident. According to the literature, the purity of carbon tetrachloride is most important in the extraction procedure. The slightest traces of contaminants or decomposition products in this reagent will react with some Io3Ru04 during the extraction process and will prevent its removal from the aqueous phase. Many workers claim that, unless carbon tetrachloride is specially purified before use, the extraction of R u 0 4 into carbon tetrachloride will be only 90 to 95% complete. Tests were performed to verify the purity of this reagent. SpectrAR carbon tetrachloride was purified by distillation. The middle fraction of the distillate was used for the extractions. No significant difference was found between purified and the offthe-shelf carbon tetrachloride since the additional purification did not improve the separation of Io3Ru and 103rnRh. Some preliminary tests were done to evaluate the use of two other oxidizing agents, sodium bromate and silver peroxide. In sulfuric acid medium, the oxidation potential of sodium bromate is the same as ceric sulfate, but the potential of silver peroxide is higher. Yet sodium bromate and silver peroxide appeared to be only slightly better oxidizing agents than ceric sulfate. In both cases, the lo3Ru contamination levels were about 1%lower than those with ceric sulfate. However, the use
of the bromate or the peroxide introduces complications into the extraction procedure. The bromate slowly decomposes producing bromine gas and the silver peroxide produces a precipitate during the extraction process. Tests indicate that a fuming time of 80 min and an oxidation time of 10 min were optimal for the sample sizes used in this study. Samples of equilibrium 103R~-103mRh were evaporated to dryness, reconstituted with hot sulfuric acid or with hot hydrochloric acid, and then carried through the extraction procedure. Fuming a sample to dryness was very detrimental to the subsequent extraction of l03Ru, but it had no effect on 103mRhyields. Approximately 40% of reconstituted lo3Ruwas not extracted by the organic phase. I t should be mentioned that, even with repeated evaporation to dryness, there were no isotopic losses by volatilization, nor was secular equilibrium disturbed. The extraction is fast and simple. Rhodium-103m yields are good and the lo3Ru can be completely recovered and used again. The fact that the loBrnRhsulfato complex is highly stable gives reason to believe that logmRhcan be successfully isolated in a pure form suitable for biological usage. It is believed that the procedure is sound, and that, with some additional work, the extraction of loSmRhfrom lo3Ru can be
made quantitative. Furthermore, the extraction system used in this study might be applicable to the large scale recovery of rhodium.
LITERATURE CITED T. Lengyel, "Preparation and Control of Rhodium-103m Radiopharmaceuticals", IAEA. STIIPUB/294, 137, 1971. C. Rohrmann, /sot. Radiat. Techno/.,6, 352 (1969). A. LeRov. Ed., "A ComDrehensive EibliwraDhy of Element 44, Ruthenium", BRHKFS 70-1, 1969: J. Armstrong and G. Choppin, "Radiochemistry of Rhodium", NASNS 3008, IF165
K:&ura, N. Ikeda. and K. Yoshihara, Bull. Chem. Soc. Jpn, 29,395 (1956). T. Autokratova, "Analytical Chemistry of Ruthenium", Ann Arbor-Humphrey, Ann Arbor, Mich., 1969, p 144. F. Eeamish, Talanfa, 14,991 (1967). J. Korkisch. "Modern Methods for the Separation of Rarer Metal Ions", Pergamon, New York, 1969, p 524. E. A. Hausman, US. Patent 3,166,404, Jan. 19. 1965. C. Surasiti and E. Sandell, Anal. Chim. Acta, 22, 261 (1960). M. Khan and D. Morris, J. Less-Common Met., 13, 53 (1961). M. Khan and D. Morris, Sep. Scl., 2, 635 (1967). I. Kolthoff and E. Sandeil, "Textbook of Quantitative Inorganic Analysis", 3rd ed., Macmillan, New York. 1952, p 582.
RECEIVEDfor review January 8, 1976. Accepted March 4, 1976. Work supported in part by the United States Public Health Services under Grant No. 3-T01-FDO-1008.
Field Desorption Mass Spectrometry of Biogenic Amines and lsoquinoline Alkaloids: Some Comparisons with Chemical Ionization Results Gordon W. Wood* and Ning Mak Department of Chemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4
Alan M. Hogg Department of Chemistry, The University of Alberta, Edmonton, Alberta, Canada
Field desorption mass spectrometry has been shown to give molecular ions for several structural types of 2-arylethylamines, both as free bases and as salts. Synthetic samples of isoquinoline alkaloid derivatives, which may arise from in vivo condensation with aldehydes, were also studied. Comparative results obtained using other ionization techniques are included.
Field desorption mass spectrometry (FDMS) is a relatively new technique with potential for analysis of a number of important classes of biological compounds. Biogenic amines constitute one such class, the chemical ionization mass spectral (CIMS) properties of which have been published recently ( 11. Since a t least part of the advantage of CIMS arises from stability of the protonated molecular ion, we undertook a comparative FD study where additional advantage may be expected from the fact that gentle heating is sufficient to cause desorption. One context in which analysis of biogenic amines is of interest involves the alleged formation of isoquinoline alkaloids from condensation with acetaldehyde derived from ethanol ingestion (2, 3 ) . We therefore include a number of synthetic isoquinoline alkaloids in this study. In addition, several cross comparisons between various methods of ionization-electron impact (EI), CI, and field ionization (F1)-are included.
EXPERIMENTAL Field desorption and electron impact mass spectra were obtained on a Varian Model CH 5 DF Spectrometer with FD/CI/EI source. For field desorption measurements, samples were applied by the dipping technique ( 4 )to a 10-k tungsten wire which was conditioned (PhCN) a t 40 mA (Varian procedure). The source was unheated (-80 "C) except for a current applied directly to the tungsten wire anode. Anode potential was +3 kV and the cathode was generally at -7 kV. Spectra were recorded electrically on light-sensitive paper calibrated by a Hall probe mass marker. The mass scale was established by comparison with the spectrum of perfluorokerosene run under identical scanning conditions in the E1 mode. Scan rate was generally 25 amu/sec. Spectra were qualitatively reproducible but, since fragmentation is a sensitive function of anode heating current, some quantitative differences were observed in spectra run with different anodes at the same current. This effect no doubt arises from temperature differences related to varying anode resistance. Chemical ionization spectra were obtained on a modified AEI MS12 mass spectrometer ( 5 ) combined with an AEI DS50 on-line data system. In most cases, the source was held a t 150 "C and the sample heated independently to a temperature giving adequate vapor pressure. Where temperatures in excess of 150 "C were required, both source and sample were heated to about the same temperature. Ammonia a t a pressure of about 0.6 Torr was used as a reagent gas throughout because experience in this laboratory has shown that it gives the greatest ion current due to the protonated molecular ion with amines, and its relatively high boiling point is well suited to our liquid nitrogen trapped vacuum system. Methane and isobutane were also evaluated but, as was to be expected, a greater degree of fragmentation ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
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