required to separate B from C is 12 000 or 20 000 a t the collector, while 22 000 or 36 000 a t the collector is required to separate A from B or C from D. This quartet represents about 0.15% of the total ionization. Although the mass spectrum does not provide direct evidence for the structures found in these mixtures, one may attempt an interpretation of the results in Table V, based on literature results and evidence from other methods. The nitrogen types (C,HZ,+~ NH) show a relatively high concentration of material in classes x = -10, -16, and -22 corresponding to alkyl indoles, carbazoles, and benzocarbazoles, respectively, all benzologues of pyrrole. Somewhat lower concentrations of material are found in classes x = -12 and - 18 corresponding to alkyl quinolines and benzoquinolines. All of these nitrogen types are commonly observed in petroleum (7). The % N calculated from the analysis agrees well with the results of elemental analysis (Dumas method). The oxygenated compounds observed include a series with the formula C,H2,02, corresponding to saturated acids or esters. Molecular ions were observed from carbon numbers C14 to C19 and fragments were observed a t CIS and lower carbon numbers. Other oxygenated materials may include naphthenic acids and aromatic alcohols. Using the separation procedure described here, benzologues of furan do not elute in this fraction and are not present in the sample, although they may be observed in the high resolution mass spectrum of the nonpolar fraction eluted with pentane. The % 0 calculated from the analysis is significantly lower than the value obtained from elemental analysis. This is probably due to the expected low sensitivity and the relatively high abundance of the C,Hz,02 type. The types of material (C,H2n+xNHO) containing the NHO heteroatom group between X = - 4 and X = -18 include amides, evidenced by substantial absorption in the infrared a t 1670 cm-l. The material in classes X = -6, -12, and -18 may correspond to alkyl pyridones and their benzologues. There is enough nitrogen and oxygen to account for the entire sample, assuming one nitrogen or oxygen per molecule, and enough sulfur t o account for an additional 30%. I t is probable that there is very little hydrocarbon present, and that the observed 47% hydrocarbon intensity consists primarily of fragments from heteroatomic material. Some sulfur containing fragments in benzothiophene, dibenzothiophene, and other classes were also observed. However, because of the large amount of nitrogen and oxygen present, the mass measurements are not sufficiently accurate to obtain reliable estimates of the distribution of sulfur, since the mass difference between compounds Cn--3H2n+4+xS and C, H Z , + ~ is only 0.0034 amu. Consequently, sulfur containing types with the formula Cn-3H2,+4+ ,S are included in the hydrocarbon class C,HP,+~.
I t is not possible to indicate the magnitude of the errors in the analysis since reliable independent methods of analysis are not available. Although the nitrogen content estimated from the analysis is in reasonably good agreement with the value determined by elemental analysis, the estimated oxygen content is too low and the hydrocarbon content is too high. Sensitivity corrections and corrections for hydrocarbon fragmentation could be made, but because of the variability and complexity of typical samples, we have not yet been able to incorporate these corrections into a general program applicable t o most samples. Rough corrections can be made, based upon the elemental analysis of each sample, and may provide a somewhat more accurate composition. In summary, the analysis is useful in providing comparisons of composition between samples of polar petroleum fractions containing heteroatoms. For example, the method can be used to identify the relative amounts of nitrogen types in shale oils or petroleum products, and to identify sulfur and oxygen types not usually determined. When applied to aromatic petroleum fractions, the method has the advantage of being consistent with the widely used analysis developed by Robinson and Cook.
LITERATURE CITED (1)H. E. Lumpkin, Anal. Chem., 28, 1946 (1956). (2)A. Hood and M. J. O'Neal, "Advances in Mass Spectrometry", Vol. 1, J. D. Waldron, Ed., Pergamon Press Ltd., London, 1959,pp 179-192. (3)C. J. Robinson and G. C. Cook, Anal. Chem., 41, 1548 (1969). (4)C. J. Robinson and G. C. Cook, Anal. Chem., 43, 1425 (1971). (5)E. J. Gallegos, J. W. Green, L. P. Lindeman. R . L. LeTourneau, and R . M. Teeter, Anal. Chem., 39, 1833 (1967). (6)T. Takeuchi, K. Matsumoto, and N. Yamamoto, Sekiyu GakkaiShi, 12,929 (1969). 41,1084 (1969); L. R . Snyder, (7)L. R. Snyder, Anal. Chem.,41,314(1969); B. E. Buell. and H. E. Howard, Anal. Chem., 40, 1303 (1968). (8)Thomas Aczel, D. E. Allan, J. H. Harding, and E. A. Knipp, Anal. Chem., 42, 341 (1970). (9)T. Aczel, J. Q.Foster, J. H. Karchmer, Am. Chem. SOC.Div. Fuel Chem. Prepr., 13,(l),8 (1969). (10)K. Biemann, Adv. Mass Spectrosc., 4, 139 (1968):R. Venkataraghaven. F. W. McLaffertyand J. W. Amy, Anal. Chem., 39, 178 (1967). (11) D. D. Tunniciiff and P. A. Wadsworth, Anal. Chem., 40, 1826 (1968). (12) W. R. Middleton, Anal. Chem., 39, 1839 (1967). (13)E. Darnenburg and H. Hintenberger, Z.Naturforsch, A, 18,676 (1961). (14) J. M. Hayes, Anal. Chem., 41, 1966 (1969). (15)S.Kinoshita, Proc. R. SOC.London, 83A, 432 (1910). (16)K. I. Grais, Appl. Spectrosc., 23, 607 (1969). (17)D. M. Desiderio, "Mass Spectrometry: Techniques and Applications", G. W. A. Miine. Ed.. Wiiey-interscience, N.Y., 1971,pp 11-42. (18)S. H. Hastings, B. H. Johnson, and H. E. Lumpkin. Anal. Chem., 28, 1243 (1956). (19)B. A. Orkin, J. G. Bendoraitis, B. Brown, and R. H. Williams, ASTM Special Tech. Pub., No. 224. Symp. on Composition of Petroleum Oils, 59,ASTM, Philadelphia, Pa., 1958. (20)B. Sirnoneit, H. Schnoes, P.Haug, and A. C. Burlingame, Chem. Geol., 7 , 123 (1971); Nature(London), 228, 75 (1970). (21)M. 0. Rosenheimer and J. R. Kiovsky, Am. Chem. SOC.Div. Petrol. Chem. Prepr., 12,(4),147 (1967).
RECEIVEDfor review August 6,1975. Accepted February 17, 1976.
Determination of Uranium in Natural Waters by Neutron Activation Analysis Ernest S. Gladney," James W. Owens, and John W. Starner Los Alamos Scientific Laboratory, P.O. Box 1663, Los Alamos, N.M. 87545
A rapid procedure has been developed for the measurement of uranium in natural waters using thermal neutron activation and anion-exchange separation of radio-uranium from ethanol/HCI solvent mixtures. Detection limits of 0.05 ppb have
been achieved with analytical precisions of f10-30%. Results of uranium analyses by this procedure and by fluorometry are compared for natural water samples from Alaska and New Mexico. ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
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Table I. Uranium Concentrations in Natural Waters, ppb LocaSample tion No. Column Fluorometry Alaska 1 0.44 & 0.09 0.26 f 0.05 2 0.60 f 0.10 0.26 f 0.05 3 1.4 f 0.2 1.7 f 0.09 4 0.04 f 0.04 0.08 f 0.08 5 0.22 f 0.06 0.17 f 0.17 6 0.34 f 0.07 0.30 f 0.10 7 0.26 f 0.07 0.23 f 0.12 8 0.15 f 0.05 0.14 0.07 9 0.23 f 0.06 0.15 f 0.08 10 0.05 f 0.05 0.11 f 0.08 11 0.74 f 0.09 0.53 f 0.08 12 0.47 f 0.06 0.58 f 0.08 13 1.6 f 0.2 1.7 f 0.1 14 0.22 f 0.05 0.17 f 0.17 15 0.11 f 0.05 0.04 f 0.02 16 0.26 f 0.05 0.23 f 0.05 17 0.18 f 0.05 0.13 f 0.04 18 0.03 f 0.05 0.02 f 0 . 0 2 19 0.31 f 0.05 0.61 f 0.15 20 0.02 f 0.04 0.02 f 0.02 New Mexico 1 24 & 2 28 f 4 2 11 f 1 8.9 f 1.8 3 9.5 f 0.8 9.7 f 0.9 4 2.0 f 0.2 2.0 f 0.5
Most estimates of the proven U reserves in the world indicate that a serious shortage of U may occur as electric utilities increasingly switch from fossil fuel to nuclear fuel ( I ) . Several advanced geochemical methods are currently being used for searching out new U ore bodies. Perhaps one of the best geochemical techniques involves the analysis of ground waters and lake sediments for U and plotting U concentration contours to aid in the location of buried deposits ( 2 , 3 ) .Several nations, including the United States, have large scale sampling programs under way that will require tens of thousands of U determinations in natural waters at sub-ppb levels (1,4-6). Two analytical methods are commonly employed for these determinations: delayed neutron counting (7) and fluorometry (8).Although the latter is the more sensitive technique, it can suffer from quenching interferences by iron and other dissolved trace elements (8).Two ion-exchange procedures (9, I O ) , which have been reported recently, eliminate these interferences, but they require extensive laboratory treatment of large volumes of water. This paper describes a method of U measurement which couples neutron activation and anion exchange separation of U from small volumes of water. This technique, which is,amenable to the analysis of large numbers of samples rapidly, is currently being used for the determination of U in a portion of the water samples collected for the U S . Energy Research and Development Administration’s Hydrogeochemical Stream Sediment Survey program. EXPERIMENTAL Uranium was separated from neutron irradiated water samples by preferential retention on Bio-Rad AG 1 X 2 anion exchange resin (50-100 mesh; chloride form) which had been pretreated with an ethanol/HCl mixture. A column 5 cm long and 1 cm in diameter was prepared from resin which had been soaked for 1h in a 4 : l (v/v) solution of ethanol/HCl. The resin was contained in thin-walled polyethylene tubing to minimize the absorption of low energy y-rays from U. Three ml of water (acidified at the time of collection with up to 1% ”03) was irradiated for 10 min in a thermal neutron flux of 5 X 10l2 n/cm2/s in one of the pneumatic transfer facilities of the Los Alamos 974
ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
Table 11. Standard Addition of Uranium to New Mexico Water Sample No. 4 Spike recovery U added, U found, ng/ml ng/ml ng/ml % 0.0 3.3 5.7 16.7 38.3
2.0 5.2 7.7 18.9 41.8
0.0 3.2 5.7 16.9 39.8
100 97 100 101 104
Omega West Reactor. Immediately after irradiation, the water was added to 20 ml of the 4:l ethanol/HCl solution to maintain the HCl concentration above 2 M, loaded on the previously prepared column, and eluted at a flow rate of 25 ml/min using 2 kg/cm2positive pressure (compressedair). Following elution, the column was washed with two 10-ml portions of the mixed solvent,and the resin column was counted directly against the face of a horizontally mounted, coaxial, high resolution Ge(Li) detector for 10 min. The 74.5-keV y-ray from 239U ( t 1 / 2 = 23.5 min) was utilized for the analysis. The total time required for this chemical separation was less than 4 min. RESULTS AND DISCUSSION The U concentrations in natural water samples from Alaska and New Mexico are reported in Table I. Duplicates of these samples were analyzed by a fluorometric technique similar t o that described by Price e t al. ( 1 1 ) and by the procedure described in this paper. All analyses were standardized against U solutions prepared from National Bureau of Standards Standard Reference Material 950a (U308). The uncertainties quoted for the ion exchange separation are based upon the counting statistics and counting geometry, while those for the fluorometric analysis are the relative standard deviations among three separate determinations. The results of these two techniques compare well over the U concentration range of 0.1-20 ppb. T h e difference in results between techniques averages 12% of the mean for U concentrations above 1 ppb, and 35% of the mean for U concentrations below 1 ppb. In most cases, the relative uncertainties overlap, and in the few instances where there is a significant difference in results, the fluorometric value is usually the lower. This suggests that interference from quenching ions has resulted in a low measurement by fluorometry. Potential matrix interferences from unknown species in the water samples were investigated using the standard addition method. Four different concentrations of U were added t o New Mexico Sample No. 4 (Table I) and analyzed as described above. The results are shown in Table 11. There is no evidence for matrix interference with this anion-exchange separation. It has also been suggested that dissolved “humic acids” in the water samples might complex the U more strongly than the resin column, resulting in underestimation of the U concentration (12).Investigators working in areas having waters with high levels of humic acids should be cognizant of this potential problem and check questionable samples by the standard addition method. The uncertainty introduced by variations in the distribution of the radio-uranium on the column and by slight differences in resin heights in the columns was evaluted by 10 duplicate runs on a 2-ppb U solution and found t o be 4 3 % . In every activation determination reported in Table I, the uncertainty resulting from counting statistics dominated that from the counting geometry. The practical detection limit achieved by this solumn separation is about 0.05 ppb U, comparable with t h a t of direct fluorometry. Although anion exchange of U occurs from water/HCl solutions, the substitution of ethanol for water in the eluting solution is critical to the success of this rapid separation technique for two reasons. First, U distribution coefficients
between resin and solvent phases have been measured to be 5000 for ethanol/HCl and 20 for water/HCl solutions when the HC1 concentration is maintained above 2 M (13).T h e retention of U is unaffected by small changes in experimental conditions (elution rate, acid molarity, and ethanol/HCl ratio). Second, significant amounts of the U can be eluted from the column during the washing cycle when a water-based mixture is employed. No U release has been observed for U sample concentrations of up to 2 ppm when the ethanol-based mixture is used. Decontamination factors are shown in Table I11 for common short-lived activation products which interfere with the measurement of the low energy 239Uy-ray. These were determined by comparison of y-ray spectra from the ion exchange columns with corresponding spectra from unseparated, irradiated water samples counted in similar geometries. T h e column retains approximately 5% of the Br, Mn, Mg, and V; approximately 2% of the Cl, Al, and Ca; and approximately 1%of the Na and K. For t,he water samples studied, this degree of decontamination results in a peak-to-Compton background ratio of 1:l for 0.1 ppb U. The use of a Low Energy Photon Counting System would further eliminate much of the Compton background in the 74-keV region. This neutron activatiodanion exchange technique exhibits the same detection limits and precision as direct fluorometric analysis of water samples. T h e principal advantage is its insensitivity to unknown levels of chromophors (e.g., Fe, Cr, and Cu) which quench the U fluorescence and cause substantial underestimation of U concentrations by direct fluorometry. This activation method is rapid and requires considerably less laboratory preparation of samples or resins than an anion exchange/fluorometric technique described by Korkisch and Godl (9) or a Chelex lOO/x-ray fluorescence method recently reported by Hathaway and James (10).
Table 111. Decontamination Factors for Anion Exchange Separation of U Element I Br
v
Mn Mg
DF 3 16 16 20 24
Element A1 Ca
c1
Na K
DF 34
36 38 70 > 100
ACKNOWLEDGMENT The authors thank Priscilla Jose for her assistance with the fluorometric analysis; David Curtis and Ken Apt for their critical comment on the manuscript; and the staff of the Omega West Reactor for their assistance. LITERATURE CITED (1) U S Energy Research and Development Admin., A National Plan for Energy Research, Development and Demonstration: Creating Energy Choices for the Future, USERDA Rep., ERDA-48, June 1975. (2) H. Fauth. "Uranium Exploration Methods", International Atomic Energy Agency, Vienna, 1972, pp 209-218. (3) W. Dyck and E. M. Cameron, Geol. Surv. Can. Pap., 75-1, Part A., pp 209-212. (4) A. A. Saukoff, Proc. UNlnt. Conf. At. hergy, Geneva, 6, 756-759 (1955). (5)J. Plant, Trans. Sect. 8,lnst. Min. Metall., 80, London, 1971. (6) A. Y. Smith and J. J. Lynch, Geol. Surv. Can. Pap., 69-40, 1969. (7) S.Amiel, Anal. Chem., 34, 1683 (1962). (8) L. L. Thatcher and F. B. Barker, Anal. Chem., 29, 1575 (1957). (9) J. Korkisch and L. Godl, Anal. Chim. Acta, 71, 113 (1974). (10) L. R. Hathaway and G. W. James, Anal. Chem., 47, 2035 (1975). (1 1) G. R. Price, R. J. Ferretti, and S . Schwartz, Anal. Chem., 25, 322 (1953). (12) D. A. Becker, National Bureau of Standards, private communication, 1976. (13) J. Korkisch. P. Antal, and F. Hecht, J. lnorg. Nucl. Chem., 14, 247 (1960).
RECEIVEDfor review December 5,1975. Accepted February 23, 1976. This work was supported by the US.Energy Research and Development Administration.
Selective Foam Fractionation of Chloride Complexes of Zinc(ll), Cadmium(H), Mercury(ll), and Gold( 111) Wladyslaw Walkowiak,' Dibakar Bhattacharyya, and R. B. Grieves* DepaHmentof Chemical Engineering, The University of Kentucky, Lexington, Ky. 40506
An experimental investigation is presented of the batch foam fractionation of the chloride complex anions of Zn( II), Cd(ll), M (metal concentration) Hg(ll), and Au(lll) from 1.0 X acidic aqueous solutions with the cationic surfactant hexadecyltrimethylammonium chloride. The effect on metal separation is established of the presence of CI- over the concentration range 0.01 to 3.0 M, both for solutions containing a single metal and for solutions equimolar in the four metals. At a 0.01 M concentration of chloride, Au(lll) can be efficiently foam-fractionated from the other three metals and, at a 0.5 M concentration of chloride, Au(lll) and Hg( II) can be efficiently foam-fractionated from Cd( II) and Zn( 11).
T h e effectiveness of a physicochemical method of concentration and separation is principally determined by its selectivity. Foam fractionation relies on the interactions of a n Present address, Institute of Inorganic Chemistry and Metallurgy of Rare Elements, Technical University of Wroclaw, Wroclaw, Poland.
ionogenic surfactant with oppositely-charged ions in solution and a t solution-gas bubble interfaces to produce a most significant enrichment of selected ions in a foam formed above a n aqueous bulk solution. The foam fractionation selectivity of cationic surfactants for inorganic anions has been studied in several recent investigations (1-9). The ionic structure of a solution of complex compounds depends on the stability, solubility, and other physicochemical properties of the solution components. The type of complexation process utilized to convert metallic cations into anions primarily determines the resultant ionic charge. Complexation with simple ligands such as C1-, CN-, SCN-, or S ~ 0 3 ~ is readily achieved, and transition metal complexes with these ligands are remarkably stable and can be obtained easily, both in the laboratory and on a larger scale. The enrichment and separation of metal complexes by foam fractionation has considerable promise. Jacobelli-Turi et al. (10) have utilized the fact that ThflV), unlike U(VI), does not form chloride complexes and were able to separate the metals in 8 M HCl medium with a cationic surfactant of the R4N+ type. T h e same type of surfactant ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
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