ANALYTICAL CHEMISTRY, VOL. 51, NO. 7, JUNE 1979
in the presence of various other ions.
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(10) J. Vesely, Collect. Czech. Chem. Commun., 39,710 (1974). (11) I. C. Popescu, V. Ciovirnache, L. Savici, and C. Liteanu, Rev. Roum. Chim., 18, 1459 (1973). (12) N. Boltazzini and V. Crespi, Chim. Ind., 52, 866 (1970). (13) C. Liteanu, 1. C. Popescu, and V. Ciovirnache, Talanta, 19, 985 (1972). (14) J. Koryta, "Ion Selective Electrodes", Cambrage University Press, London, 1975. (15) J. W. Illingworth and J. F. Keggin, J. Chem. SOC.,575 (1935). (16) C. J. Coetzee and A. J. Basson, Anal. Chim. Acta, 64, 300 (1973). (17) D. Ammann, E. Pretsch, and W. Simon, Anal. Lett., 5, 843 (1972). (18) R . J. Levins, Anal. Chem., 44, 1544 (1972).
LITERATURE CITED (1) A . V. Gordievskii, A. F. Zhukov, V. S. Shterman, N. I. Savvin, and Y . I. Urusov, Zh. Anal. Khim., 29, 1414 (1974). (2) A. V. Gordievskii, A. F. Zhukov. Y. I. Urusov. and V. Shterman, Zh. Anal. Khim., 29, 1298 (1974). (3) E. Hopirtean and E. Stefaniga, Rev. Roum. Chim., 19, 1265 (1974). (4) T. S. Light and J. L. Swartz, Anal. Lett., 1, 825 (1968). (5) R . Bock and H. J. Puff, Fresenius' 2. Anal. Chem., 240, 381 (1968). (6) M. Mascini and A. Liberti. Anal. Chim. Acfa, 51, 231 (1970). (7) E. Pungor and K. Toth, Analyst(London), 95, 625 (1970). (8) I. C. Popescu, C. Liteanu, and L. Savici, Rev. Roum. Chim., 18, 1451
RECEIVEDfor review November 7 , 1978. Accepted January 23,1979. The authors are thankful to the University Grants Commission, New Delhi, for financial assistance.
(1973). (9) C. Lieanu, I. C. Popescu, and V. Ciovirnache, Stud. Unlv. Babes-Bolyai, Ser. Chim., 18, 53 (1973).
Determination of Americium in Small Environmental Samples Daryl K n a b Environmental Surveillance Group, Los Alamos Scientific Laboratory,
Americium in the environment is being determined as part of surveillance and research programs related to nuclear industries ( 1 , 2 ) . T h e analysis of environmental samples for americium is difficult since americium is chemically similar to several common matrix materials. Most analytical procedures for americium in complex matrices, therefore, tend to be long and tedious (3-5). Some environmental samples, particularly in surveillance or biological research, may not be large in terms of total dissolved mass although they still tend to be complex. For these smaller samples, it is unnecessarily costly to process them through procedures designed for larger samples. A procedure has been developed that is suitable for analysis of complex matrix samples of less than approximately 2 g of ash. It is moderately short, utilizing two ion-exchange columns a n d electrodeposition, and is simple enough that many samples can be processed at a time. Tracer recoveries generally exceed 80% and samples are chemically and radiologically pure enough for alpha spectrometric analysis.
EXPERIMENTAL Special Materials a n d Reagents. The ion-exchange resins, AG 50-X8, 100-200 mesh; and AG MP-1, 100-200 mesh, are available from Bio Rad Laboratories, Richmond, Calif. They are water washed before use t o remove fines. Other reagents are USP or analytical grade and are used as received. The ion-exchange column tubes are 19 cm x 0.7 cm i.d. with a 100-mL reservoir on top. The tips are tapered and packed with glass wool to contain the resin. Procedure. Add a known amount of 243Amtracer to each sample. Dissolve samples by the method preferred for the matrix being analyzed. Convert the residue to the chloride form and dissolve in 50 mL of 0.5 M HC1. Pass the sample through a 17-cm column of settled AG 50-X8 resin preconditioned with 50 mL of 0.5 M HC1. Wash the column with five 25-mL portions of 2.0 M HC1. Elute americium with 75 mL of 4 M HCl. Add 5 mL of H N 0 3 to the americium eluate, and evaporate just dry. Dissolve the residue in 2 mL of 6 M HNO,. Add 3 mL of ethanol saturated with NaN02,just prior to loading on the anion column. Load onto an 11-cm column of settled AG MP-1 resin preconditioned with 40 mL of 60% ethanol-40% 6 M "Os. Wash the sample beaker and column with 5 mL of 60% ethaWash the column twice with 20 mL of 75% nol-40% 6 M "OB. methanol-25% 6 M HNO,. Wash the column twice with 20 mL of60% methanol-40% 6 M HN03. Elute americium with 30 mL of 60% methanol-40% 2.5 M "Os. Evaporate the americium eluate to 1 mL on low heat. Add 5 mL of HCl and evaporate just dry. Add 5 mL of HC1 and evaporate just dry. Add 2 mL of 1 M HCl, 0.5 mL of saturated NH,Cl, and 1 drop of methyl red indicator. Neutralize with 0003-2700/79/0351-1095$01 .OO/O
Los
Alamos, New Mexico 87545
dropwise addition of NH40H. Back titrate just pink with 1 M HC1. Transfer to a plating cell and electrodeposit with a current of 0.6 A onto a 12-mm diameter stainless steel surface. Continue the electrodeposition until the plating solution evaporates to the top of the platinum anode, -0.5 cm from the disk. Quench the solution with 10 mL of 5% NH40H. Rinse the plate with water and acetone. Heat the disk briefly on a hot plate at 220 "C. Determine americium by alpha spectrophotometry.
RESULTS AND DISCUSSION S a m p l e Dissolution. In environmental studies, sample matrices tend to be highly variable in nature and chemical composition. Each matrix, and often each sample, requires specific dissolution techniques. In general, samples are either geological, biological, or hydrological; however, vegetation samples frequently appear to be geological samples once they are ashed because of relatively large amounts of soil associated with the plants. T h e same is true of animal hides and stomachs as well as water and air filter samples. In this laboratory, samples are dry ashed overnight a t 500 "C before wet ashing or wet ashed directly, depending on sample size and organic content and nature. Geological, vegetation, air filter, and water samples are wet ashed in HN03-HF and HN03-HzOz as needed; residual fluoride must be complexed with &Bo,. Bone and tissue samples are dissolved with HNO3-H2O2and, if necessary, HN03-HC104. Fusion dissolutions can be used, but t h e large mass of t h e fusion salts may adversely affect the americium absorption on the cation column limiting the sample size. Bone samples chemically interfere with the americium retention on the cation column through the 2 M HC1 wash steps. Americium recovery from 2 g of bone ash is greater than 909'0, but decreases to 60% for 3-g samples and is essentially zero for 4-g samples. Geological sample analysis is not limited by size, but by the neodymium content. Neodymium, which is not separated by this procedure, has a crustal abundance of 24 ppm (6). Since 50 pg of macro material deposited on the Am plates begins to degrade the alpha spectra, geological sample aliquots for analysis by this procedure are limited to about 2 g even though the cation column will adequately separate americium from 5-g samples. Biologicals and other matrices, like soils, can usually be analyzed for americium from samples larger than 2 g of ash, but not always with impunity because of inadequate column retention or possible contamination of the plated samples. Cation-Exchange Column. Americium is separated from major matrix contaminants on the cation-exchange column 1979 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 7, JUNE 1979
100-
--
0 5 _M HCI --we
0
-- ,,
2 _M HCI
7
.Q
--
4
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! A
10 z
A
1:
a
-
-
0
0
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-
+
+
+
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Flgure 1. Cation-exchange column elution curves.
$ A
150
200
250
(0)Aluminum; (A)calcium; (+) iron; (0)americium
100
10
1
0.1
0 . 01 ELUATE VOLUME, m L Figure 2. Alcohol-HNO, anion-exchange column elution curves, (0)Iron; (0)strontium; (A) radium; (+) europium; (0) americium; ( X ) neodymium; (B) 7 5 % methanol-25% 6 M "0,; (C) 60% methanol-40% 6 M "0,; (D) 60% methanol-40% 2.5 M "OB; (E) 6 M HNO,
(0)praeseodymium; (V)cerium. (A) 60% ethanol-40% 6 M "Os;
using dilute HCl (7). Figure 1 shows elution curves of americium and some of the matrix materials common to environmental samples. Much of the sample matrix is retained by the resin from 0.5 M HC1, except for alkaline metals and anionic species.
This limits sample mass to about 2 g for most matrices, above which americium retention may be adversely affected. Major constituents are eluted with 2 M HC1 giving decontamination factors greater than lo4. Yttrium is about 90% separated, but europium is eluted with americium. Thorium and much of
ANALYTICAL CHEMISTRY, VOL. 51, NO. 7, JUNE 1979
the plutonium(1V) are retained on the column after americium elution. Anion-Exchange Column. The anion-exchange column in alcohol-nitric acid ( 4 ) , as modified, is very selective for americium with neodymium being the only identified major interference. T h e column is not very tolerant of macro interferences, because of low solubility of material in ethanol-nitric acid solution and the necessity of low load solution volumes. T h e load volume can be increased, but americium recoveries and contaminant separations are affected above about 20 mL. T h e column can be run using AG 1-X4 anion-exchange resin, but the large porosity of the macro porous resin, AG MP-1, alleviates equillibrium problems encountered with alcohol-mineral acid eluants in ion-exchange systems (8, 9). Elution curves for several elements from AG MP-1 are shown in Figure 2. Matrix materials elute very fast with iron showing little, if any, absorption. Based on the strontium curve, calcium also will elute rapidly. Radium elutes slowly, tailing even further than europium, b u t i t does separate adequately, which is a real advantage t o this column. Radium and some of its daughters from the thorium and uranium decay chains interfere directly with alpha spectrometric determination of americium. Since Southwestern soils tend t o be high in uranium a n d thorium, radium contamination is a constant problem for much of t h e work in this laboratory. The rare earth elements split on this column with samarium to lutetium eluting ahead of americium. Neodymium and probably promethium elute with americium. Praeseodymium, cerium, and lanthanum are left on the column with t h e thorium and plutonium(1V). Plutonium(II1) elutes, at least partially, with americium. Curium is separated from americium, eluting ahead of it ( I O ) . Americium-curium separation factors have not been determined, but appear to exceed 100. Minor adjustments in elution conditions probably will yield good americium, curium, berkelium, and californium separations. Americium Electrodeposition. The electrodeposition of americium from NH4C1media neutralized to the methyl red
1097
end point has been found to be the most reliable plating method (11). Environmental samples, even after extensive purification, often contain sufficient contamination to slow t h e americium plating rate, without affecting alpha peak resolution. At some period during evaporation of the NH4Cl plating solution, conditions necessary for complete deposition of americium are attained. Electrodeposition from oxalate (12) or sulfate (13) solutions, which works very well for pure solutions, does not result in evaporation of the plating solution and long plating times, many hours, are required for complete electrodeposition. I t is necessary to prevent the NH4Cl solution from evaporating too far. If the samples are not quenched before electrical contact is broken, americium and stainless steel are rapidly stripped from the disk. LITERATURE CITED (1) T. E. Hakonson, J. W. Nyhan, L. J. Johnson, and K. V. Bostick, Los Alamos Scientific Laboratory Report LA-5282-MS (1973). (2) Environmental Surveillance Group, Los Alarms Scientific Laboratory Report LA-7263-MS (1978). (3) R. Bojanowski, H. D. Livingston, D. L. Schneider, and D. R. Mann, Woods Hole Oceanographic Institution, COO-3563-8 (1973). (4) D. Knab, Los Aiamos Scientific Laboratory Report LA-7057 (1978). (5) W. J. Majors, K. D. Lee, and R. A. Wessman, "Analysis of *=Pu and *"Am from NAEG Large Size Bovine Samples", in "TheRadioecology of Plutonium and Other Transuranlcs in Desert Environments", M. G. White and P. B. Dunaway, Ed., NVO-153, 1975, pp 449-463. (6) R . C. Weast, Ed. "Handbook of Chemistry and Physics", 56th ed., CRC Press, Cleveland, Ohio, F195 (1976). (7) R . A. Penneman and T. K. Keenan, "The Radiochemistry of Americium and Curium," National Academy of Sciences, National Research Council, NAS-NS-3006 (January 1960). (8) L. I.Guseva and G. S. Tikhomlrova, Radiokhimiya, 18. 152 (1974). (9) S.F. Marsh, M. R. Ortiz, R. M. Abernathey, and J. E. Rein, Los Alamos Scientific Report LA-5566 (1974). (10) L. I.Guseva and G. S. Tikhomirova, Radiokhimiya, 15, 401 (1973). (11) R. F. Mitchell, Anal. Chem., 32,326 (1960). (12) F. L. Moore and G. W. Smith, Nucleonics, 13,66 (1955). (13) I. K. Kressin, Anal. Chem., 49, 842-846 (1977).
RECEIVED for review October 6,1978. Accepted March 5,1979. This work was performed under the auspices of t h e United States Department of Energy. A presentation on t h e procedure was made at the Twenty-fourth Conference on Bioassay, Environmental and Analytical Chemistry, October 17-19, 1978 in Annapolis, Maryland.
Determination of the Nitrogen Content of Hydrotreated Shale Oil Furnace Oil by Refractometry Jacques Saint-Just*' and Olaf A. Larson Gulf Research & Development Company, P.O.Drawer 2038, Pittsburgh, Pennsylvania 15230
T h e nitrogen content of petroleum fractions is usually determined by digestion or combustion methods. Even when partially automated, these cumbersome methods cannot easily be adapted to process control. This drawback may become critical if nitrogen is t h e primary factor to be monitored, as it is in shale oil hydrotreating. In this paper, it is shown that the refractive index, which is one of the most easily measured physical parameters, can be used to determine the nitrogen content of the hydrotreated products of a shale oil furnace oil. Moreover, the index of refraction of liquids can be easily followed continuously through process refractometers. EXPERIMENTAL Materials. Hydrotreated hydrocarbons of various nitrogen content were obtained by high-pressure hydrogenation of a parah0 'Present address: Gaz de France, D.E.T.N., 75840 Paris, Cedex
17, France.
0003-2700/79/0351-1097$01 .OO/O
Table I. Shale Oil Furnace Oil Properties boiling range, C gravity, ' API nitrogen, wt % oxygen, wt 3'% sulfur, wt 7c saturates, w t % olefins, wt % aromatics. wt %
203-350 28.1 1.74
1.30 0.70
52.2 24.3
23.5
shale oil furnace oil at different conditions and over different catalysts in a trickle bed mode. Some of the properties of that feedstock are given in Table I. The reaction temperature and pressure ranged from 361 to 393 O C and from 3.4 t o 10.3 MPa, resDectivelv. The sDace velocitv was varied between 0.28 and 1.12 ks-i. The gas rate was either 690 or 1780 m3 of hydrogen (STP) per m3 of oil. Hydrogenation and hydrocracking catalysts were used for the hydrotreatment. They included Co-Mo, Ni-Mo, 'C 1979 American Chemical Society
