2394
Anal. Chem. 1983, 55, 2394-2398
Separation and Mass Spectrometry of Nanogram Quantities of Uranium and Thorium from Thorium-Uranium Dioxide Fuels L. W. Green,* N. L. Elliot, and T. H. Longhuret Atomic Energy of Canada Limited Research Company. Chalk River Nuclear Laboratories, Chalk River, Ontario, Canada KOJ 1JO
A convenlent and sensltive microchemical procedure was developed for the separatlon and Isotopic analysls of U and Th from Irradiated (Th,U)02 fuel. The separatlon procedure consisted of two stages; In the flrst a trlbutyl phosphate lmpregnated redn bead was equlilbrated with the dlssolved fuel in 0.08 M HF/6 M HNO, solution. The bead sorbed approxlmately 1.7 pg of U and 4.8 pg of Th and provided good separatlon of these from the fisslon products. I n the second stage, the U and Th were back-extracted Into 0.025 M HF/8 M HNO, soiutlon, whlch contalned a small anion-exchange membrane dlsk. The disk adsorbed approxlmately 14 ng of U and 45 ng of Th, and subsequently was transferred to the ionizing fllament of a thermal-ionizatlon mass spectrometer and covered with a starch deposlt. Sensltlvitles were sufflclently high for sequential analysis of these quantltles of Th and U from a single dlsk. Isotopic data obtalned for a comblned U and Th standard showed excellent agreement with certifled values: overall bias and precision were G 0 . 0 3 % and 0.2 % relative standard deviation, respectively, for both elements. The applicablllty of the procedure to uranium fuels was also demonstrated.
Measurements of the extent of fission and of transmutation processes are vital to the assessment of the irradiation performance of a nuclear fuel. For a (Th,U)02fuel, these measurements involve determination of the concentrations and isotopic compositions of U and Th, for which the most suitable technique is thermal ionization mass spectrometry. Prior to isotopic analysis, the U and T h must be separated from the fission products and converted to a suitable form for mass spectrometry. Most fuel analysis procedures reported in the literature (ref 1 and references therein) use lengthy ion-exchange chromatographic or solvent extraction procedures for the separations and use solution loading of microgram quantities of the extracted actinide for mass spectrometry. Because of a large number of samples to process and the expense of hot cell time and materials, a shorter and more convenient separation procedure was desired. Furthermore, because of the relatively high specific radioactivity of zzsTh,232U,and 233U,which are produced in thorium-based fuels, and of ,h@ 32' l which is used as a spike, the quantity of T h or U used for mass spectrometry in our laboratory is limited to the nanogram level, to avoid significant radiation doses and mass spectrometer contamination. Carter and co-workers (2, 3) have developed a technique that involves batch equilibration of Dowex 1-X2 anion-exchange resin beads with the fuel solution, followed by transfer of a single bead to the ionizing filament. The resin bead enhanced the sensitivity relative to solution loading and, in combination with pulse counting detection, enabled quantitative measurements to be made on a few nanograms of U. The resin bead technique thus appeared to be an attractfive means both for simplifying the separation steps and for re-
ducing the quantity of actinides required for mass spectrometry. We tested the resin bead technique in our laboratory and confirmed that a large enhancement in sensitivity was obtained and that quantitative mass spectrometry of nanogram quantities of uranium was possible. However, for application of the technique to thorium fuels, some modifications were required. The composition of the fuel was typically 97.3% Thoz and 2.7% UOz, thus the ratio of T h to U adsorbed by a Dowex bead was expected to have been very high (-lOOO), because of the greater affinity of the beads for Th(1V) than for U(V1) ( 4 ) . The high T h to U ratio would have caused high radioactivity levels and erratic ion beams for U analysis. Experience in our laboratory has shown that a desirable T h to U ratio for mass spectrometry was ~ 3 thus , an adsorbant with a greater affinity for U than for T h was required. Additionally, manipulation of the 0.2 mm diameter resin beads in a radiochemical fume hood was an awkward step, thus a larger, more easily transferable adsorbant was desired. Tributyl phosphate (TBP) is a well-known agent for extracting the actinides from fission products in aqueous nitrate solution (5). If fluoride is present, the distribution coefficient of Th(1V) is greatly reduced; the same applies to Zr(IV) and, to a lesser extent, other fission products (5). Thus, by addition of fluoride to a nitric acid solution of the fuel followed by extraction with TBP, a separation of thorium and uranium from the fuel solution should be obtained and should yield a decreased thorium to uranium ratio in the organic phase. To adapt the above concept to a microscale, 0.6 mm diameter XAD-2 resin beads were impregnated with TBP. Distribution coefficients of Th(1V) and U(V1) were determined for a range of " 0 , and HF concentrations, and the suitability of the beads for mass spectrometry was tested. Acropor anion-exchange membrane, cut into 1mm diameter disks, was also evaluated for extraction and mass spectrometry of U and Th. As part of a comparison of the XAD-2 bead and membrane disk, their mass spectrometric sample utilization efficiencies were determined and compared with that of conventional solution loading. Following these studies, a (Th,U)02 fuel sampling and analysis procedure was developed; this paper describes the studies and the resultant procedure.
EXPERIMENTAL SECTION Reagents and Materials. To prepare the TBP-impregnated
resin beads, XAD-2 (Applied Science Laboratories) resin beads (0.6 mm diameter) were equilibrated with TBP that had been previously washed with 1 M NaOH to remove monobutyl phosphate and dibutyl phosphate impurities. For preparation of the membrane disks, Acropor (Gelman Sciences) anion-exchange membrane was cut into 1 mm diameter disks and conditioned Dowex 1-X2 (Bio-Rad Laboratories) 100-200 with 2 M "OB. mesh anion-exchange resin beads were also conditioned with 2 M HNO, prior to use. Nitric and hydrofluoric acid solutions were prepared from double-distilled nitric acid and reagent grade hydrofluoric acid diluted with deionized water. For preparation of the starchrhenium solution, high-purity rhenium metal (Rhenium Alloys, Inc.) was dissolved in 0.06 M H,02/8 M HNOBand an aliquot was added to a 42 g/L starch solution to yield a Re concentration
0 1983 American Chemical Society 0003-2700/83/0355-2394$01.50/0
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
of 0.50 g/L. A separate 42 g/L starch solution, without Re, was also prepared. Uranium(VI) solutions were prepared from U308.powder (NBS SRM U500) or uranium metal dissolved in hot nitric acid. To prepare Th(Iv) solutions,Tho2 powder or Th metal was dissolved in 0.05 M HF/13 M HN03, evaporated to dryness several times from nitric acid solution, and redissolved in nitric acid. The preparation yielded fluoride-free Th(1V) solutions. Tracer solutions were similarly prepared from 99.7% enriched 233Uand 91.5% enriched T h . Spike solutions were prepared from 99.8% enriched 235Uand 91.5 enriched 230Th;the details of the preparation and use of the spike solutions are given elsewhere (6). Polyethylene microvials (1mL volume) were used for sample transfer and equilibration. Glass rods (3 mm diameter) were pulled to a fine point for transfer of the beads or disks to a microvial or a filament. The vials and rods were cleaned in 2 M HN03 prior to use. Apparatus. A Conuclear Ltd. Model ClOO gas flow proportional a-counter, connected to a Canberra Model 816 preamplifier and a Canberra Model 895 counter, was used for a-activity measurements. A Nuclide S.U. 2.2 thermal ionization mass spectrometer, described elsewhere ( I ) , was used for isotopic composition measurements. Samples were deposited on the rhenium center filament of Cathodeon type 553 triple filament assemblies. The original center filaments were replaced with Rhenium Alloys zone-refined rhenium ribbon, 0.025 mm thick x 1 mm wide. Procedure. ( a ) Distribution Coefficients. The TBP-impregnated beads were equilibrated in solutions that contained either a 233U(VI)or a 23"l'h(IV) tracer, and the a-activity of each phase was determined. To determine the a-activity of the solution phase, 10 WLof the solution was evaporated onto an a-tray and counted. To determine the a-activity of a bead, the U or Th was back-extracted into 1M "OB, and the activity in the resultant solution was determined. Distribution coefficients for the anion-exchange membrane disks were determined in a similar manner, except that for determination of the activity of a disk, the latter was dissolved in 50 FL of concentrated "OB. In both cases, tracer concentrations of -20 pg/mL were chosen to give sorptions between 10 and 40 Bq. (b)Mass Spectrometric Sample Utilization Efficiencies. A known amount of 232Thor U(NBS U500) was deposited on the center filament of the triple filament assembly, and the ion current of the major isotope was integrated over the lifetime of the sample. Five types of filament loading forms were studied: solution, XAD-2 resin bead, Dowex 1-X2 resin bead, Acropor membrane disk, and Acropor disk covered with a starch-rhenium deposit. For the solution form, 5 pL of 20 hg/mL U(V1) solution was deposited by micropipet on the filament and then dried by resistive heating. The resin beads and membrane disks were first equilibrated in the appropriate concentration of U(V1) or Th(1V) in 8 M HN03to yield 20 ng of sorbed actinide and then a single bead or disk was transferred to the filament. The filament was resistively heated with 1 A current to adhere the bead or disk. For some experiments with the disks, 3 r L of starch-rhenium solution was deposited over the disk and heated to dryness. After sample deposition, the triple filament assembly was inserted into the mass spectrometer and degassed. The center filament current was raised gradually and the U-Th region was scanned, so as to not miss any of the U or Th emission. Once the U or Th peaks were identified, the filament was heated to 1700 "C or 1900 OC, for U or Th measurements, respectively. The major isotope was monitored with a strip chart recorder until the sample was depleted. Calculation of the utilization efficiency required knowledge of the gain of the electron multiplier, which was determined by reference to a Faraday cup detector. (c) (Th,U)02Fuel Analysis Procedure. In a hot cell, 20 g of An fuel was dissolved in 200 mL of 0.05 M HF/13 M "OB. aliquot of the solution was diluted to 16 mg/mL Th(1V) in 0.08 M HF/6 M HN03 and mixed with an aliquot of a spike solution (spiked samples only) and 30 pL of the mixture was transferred to a microvial that contained two TBP-impregnated beads (0.6 mm diameter). The microvial was transferred to an adjacent glovebox and the beads were mixed with the fuel solution and left to equilibrate for 1 h. With a pulled glass rod, one bead was N
2395
T
/
0
L CHNO,]
8 (M)
12
Flgure 1. Distribution coefficients ( D )vs. [HNO,] for TBP-impregnated XAD-2 resin beads. 80
k
4I
20
n
0
0.02
0.04 0.06 0.0% [HF] (MI
Flgure 2. Distribution coefficients vs. [HF] for TBP-impregnated XADP resin beads in 6 M "0,.
transferred to a second microvial that contained 20 r L of 0.025 M HF/8 M HN03 and three membrane disks (1mm diameter). The second microvial was transferred to a fume hood, and the bead and disks were mixed with the solution and left to equilibrate for 1h. With a pulled glass rod, one disk was transferred to the center filament of a filament assembly, and 3 pL of the starch or starch-rhenium solution was added and dried with 1.8 A current. The triple filament assembly was inserted into the mass spectrometer and the U peaks were identified, as described earlier. The center filament was heated to 1700 OC (1650 "C when starch or starch-rhenium was not used), the ion source voltages were adjusted to yield optimum peak shape and signal stability, and 20 to 30 replicate isotopic analyses of U were completed. After completion of the U measurements, the filament temperature was increased to 1900 "C and the measurement process was repeated for Th. All isotope ratios were corrected for an instrumental bias factor of 0.21% per mass unit, which favored lighter masses. The same procedure was used for UOZ and UA1 fuels, except for changes in the dissolving solution ( I ) and omission of the starch-rhenium deposit.
RESULTS AND DISCUSSION Distribution Coefficients. Distribution coefficients (D) were calculated from the activity per unit volume of disk or bead divided by the activity per unit volume of solution. A nominal volume of 70 nL was used for the 1 mm diameter membrane disks, and a typical TBP-impregnated bead volume used for these experiments was 100 nL. The results were usually reproducible within a 10% spread. Figure 1 shows the results for U(V1) and Th(1V) equilibrated with the TBP-impregnated beads in nitric acid solution of various concentrations. The beads had a high affinity for U(V1); Du reached a maximum of 86 at 6 M FINO3. DTh rose steadily until 7 M "OB, at which concentration DTh was 40, and then increased only slightly a t higher nitric acid concentrations. Figure 2 shows that F- greatly reduced the sorption of Th(IV), but reduced that of U(V1) to a much lesser extent. For example, in 0.08 M HF/6 M "OB, D T h was 0.6 whereas Du was 45. Thus the TBP-impregnated beads in a HF/HN03
2396
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
3L
2
t I
0
/
Th(TP)
/"
I
L
8 [HNO,]
12
(MI
Figure 3. Distribution coefficients vs. [HNO,] for Acropor anion-ex-
change membrane disks. solution appeared to be effective for increasing the U to Th ratio in the adsorbant. To check whether the above distribution coefficients in 0.08 M HF/6 M HN03 would be applicable during fuel sampling, the measurements were repeated with a diluted fuel solution. The concentrations of Th and U were 16 and 0.38 mg/mL, respectively, these being the concentrations required to yield sufficient quantities of the actinides for mass spectrometry. Under these conditions, Du did not change significantly but DTh increased to 3. The resultant ratio of DThto DU was suitable for sampling (Th,U)Oz fuel solutions because a Th to U ratio of -3 was obtained in the bead, and this was the ratio desired for mass spectrometry. The reduction of DTh caused by F- was likely due to the formation of cationic fluoride complexes of Th(1V) (7) and concomitant reduction in the concentration of the TBP-extractable species (Th(N03)4). The higher value of DTh obtained for the equilibration with the dilute fuel solution, compared to that obtained in the tracer experiment, was likely due to the fact that the concentration of Th(1V) (0.069 M) in the former case was almost as high as that of the complexing ligand, F-. In this situation, the degree of complexation of Th(IV) by F was likely much less than when the concentration of Th(1V) was -9 X 10" M, as in the tracer experiment, and thus proportionately more of the Th(1V) was available for formation of the tetranitrato complex. Braun and Ghersini (8) have reported that TBP appears to reduce U(V1) to U(IV) in the presence of light. This matter was not investigated in our experiments; the U(VI) distribution coefficients were measured in the presence of light, but were reproducible for equilibration times between 1 and 3 h. Figure 3 shows the results of the distribution coefficient measurements for the anion exchange membrane over a range of nitric acid concentrations. Both ions exhibited maximum adsorption between 7 and 8 M "OB, at which point Du was 5.5 and DThwas 46. Figure 4 shows that, again, fluoride greatly reduced the adsorption of Th(1V) and reduced that of U(V1) to a much lesser extent. However, since Du was relatively small, the reduction of &h was not sufficient for the membrane disks to be suitable for direct sampling of a (Th,U)OZ fuel solution. Sample Utilization Efficiencies. To calculate the sample utilization efficiency for an element, the total number of ions of the element that reached the detector was divided by the total number of atoms of the same element that were deposited in the source. The former was estimated from the integrated ion current and the latter from the known concentration and volume of solution deposited, or from the appropriate distribution coefficient. The results for five different filament loading forms are listed in Table I. The highest efficiencies, 1/500 for U and 1/10000 for Th, were obtained with the starch-rhenium
I0
0.02 L
0 04'
0 06 O
[HFl (MI
Figure 4. Distribution coefficients vs. [HF] for Acropor anionsxchange membrane disks in 8 M HNO,.
Table 1. Utilization Efficiencies element filament loading form solution TBP-impregnated XAD-2 resin bead Dowex anion-exchange resin bead Acropor anion-exchange membrane disk Acropor anion-exchange membrane disk covered with starch-rhenium
U
Th
1/100 000 signal very erratic 1/2000
1/2000
1/100 000
1/500
1/10000
covered disk, whereas the lowest efficiencies were obtained with the solution form. The efficiency of the latter for Th was so low that a measurable Th+ ion signal was not obtained. The ion signals obtained with the TBP-impregnated XAD-2 beads were too noisy and erratic for this to be a useful filament loading form. The Dowex resin bead and the Acropor disk yielded equivalent efficiencies for U. Measurement of the efficiency of the Dowex bead for Th was not attempted. The differences in the utilization efficiencies of the various forms were likely due to changes in the efficiency of the ionization process, which is dependent on the work function of the surface, the fraction of the element in the measured state (e.g., atomic vs. molecular), and the fraction of deposited atoms that make close contact with the surface. Smith et al. (9)have reported that in a reducing environment, such as that produced by the resin bead, ionization efficiencies are higher than in a nonreducing environment, such as obtained with the solution loading, because the reducing environment removes oxygen from the surface region of the filament and forms a rhenium-carbon composite that has a higher work function than pure rhenium. The Saha-Langmuir equation (10) predicts an exponential dependence of the ionization efficiency on the work function, Additionally, the reducing environment causes oxides to be reduced to the atomic state, thus enhancing the atomic ion signal. The increase in utilization efficiency obtained when the starch-rhenium mixture was deposited over the disk was possibly due to an increase in the fraction of actinide atoms that made close contact with the surface. In the absence of the starch-rhenium deposit, a significant portion of the U or Th was likely volatilized with the decomposition products of the bead or disk. This portion of the actinides would not have contributed to the ion signal, because atoms must approach the filament surface within a few atomic radii for ionization to be possible (10). The starch-rhenium deposit likely held the U and T h atoms in the surface region longer, allowing a larger proportion of them to diffuse to the filament surface to become ionized. The starch-rhenium covered disk was the optimal filament loading form studied, because it yielded steady ion beams and the highest utilization efficiencies and
because the disks were easy to manipulate in a fume hood. The effect of the presence of U on the utilization efficiency of Th (and vice versa) was investigated for the starch-rhenium covered disk because of the desire to sequentially analyze U and T h from a single disk. The utilization efficiency for T h did not change significantly when U was present, whereas that for U decreased by -&fold when >20 ng of Th was present. However, if >lo ng of U and >20 ng of T h were adsorbed, the ion signals were sufficiently strong and stable to permit sequential analysis of the two elements from a single disk. If smaller quantities were used, the signals often decayed too rapidly to permit reproducible isotope ratio measurements. The effects of U and T h on the efficiencies of each other require further investigation. Selection of Procedure. The distribution coefficient measurements showed that the TBP-impregnated beads were well silited for extracting U and T h from (Th,U)02 fuel SOlution, whereas the anion-exchange membrane was not. However, the mass spectrometry experiments showed that the TBP-impregnated beads gave noisy and erratic signals, whereas the membrane disk yielded steady signals and high utilization efficiencies, especially when covered with the starch-rhenium deposit. Thus a two-stage procedure was developed; the first stage involved equilibration of the TBPimpregnated beads in a HF/HN03 solution to extract U and T h in the desired proportions, and the second stage involved desorption of the U and T h from the bead followed by readsorption onto an anion-exchange membrane disk, to provide a suitable filament loading form for mass spectrometry. The details of the procedure are described in the Experimental Section. The quantities of U and Th sorbed by the bead were typically 1.7 and 4.8 pg, respectively. Approximately 75% of each desorbed during the second equilibration, and approximately 14 ng of U and 45 ng of Th were adsorbed by each disk. These quantities varied by up to 30% from one loading to another due to variations in bead and disk size and in solution volumes. The procedure was designed to yield the above quantities so that the ion signals would be sufficiently strong and stable for sequential analysis of the two elements from a single disk. The quantity of 230Thadsorbed by a disk was typically 2 ng, because sample (232Th)to spike (230Th)ratios of -20 were used. The combined a-activity of 2?t'h, 230Th,T J and , 233U, and their daughters, was -10 Bq per disk, which was acceptable. For the first equilibration, it was important to set the [F] just greater than that of Th4+for two reasons: first, if the [F] was lower than the [Th4+],too much T h would have been sorbed, and second, if the [F-] was much greater than the [Th4+],T h would have precipitated as ThF,(s) (7). The manipulations of the 0.6 mm diameter beads and the 1 mm diameter disks in the glovebox and fume hood, respectively, proved to be simple and quick operations, and the use of very small sample quantities kept the radiation field to low levels. The y field on contact with 30 p L of fuel solution was typically between 30 and 50 mR/h, and that on contact with the bead after removal from the fuel solution was less than 1 mR/h. These data show that the first stage was effective in separating U and T h from the fission products. Mass Spectra and Interferences. Mass spectra of blank filaments sometimes showed peaks at masses 232, 235, and 238, which were attributed to trace T h and U contamination in the rhenium filaments. To remove these impurities, the rhenium filaments were heated to 1900 O C under vacuum for 2 h. Furthermore, a starch deposit (no rhenium) was substituted for the starch-rhenium deposit used in sample preparation. Further utilization efficiency studies showed that the efficiencies obtained with the starch-covered disks were
-
.02amu/s
.IO
232
2 3 3 2 3 L 235
236
238
Figure 5. Mass spectrum of Th and U from a (Th,U)02 fuel: atom
percent fission, 2.3%; sweep rate, 0.02 amu/s; temperature, 1700 O C ; filament loading form, starch-rhenium covered Acropor disk. Table 11. Accuracy and Precision of U and Th Isotope Ratio Measurements on a Combined U and Th Standard analysis no. 1 2
3 4 5 6 av S
certified ratio % bias
atomic ratio U (235/238) Th (230/232) 0.99936 0.99787 1.00032 1.00137 1.00178 0.99628 0.9995 0.002 0.9997 -0.02
10.8157 10.8116 10.8152 10.8137 10.8556 10.7927 10.817 0.02
10.82 -0.03
comparable to those obtained with the starch-rhenium-covered disks. Figure 5 shows a typical mass spectrum of an irradiated (Th,U)02fuel sample. The relatively high 233Upeak was characteristic of fuels irradiated to high burnups. The Th signal was weak and noisy when this spectrum was taken; however, a stronger and steadier Th signal was obtained afterward by increasing the filament temperature. Pu appeared in the mass spectra during initial heating of the filament and interfered at mass 238. However, the Pu evaporated quickly and was not a significant interference when the U analysis was started. Interference from 232Uwas not a problem because of the small quantity produced (232U/232Th 3 x lo4) and because U signals rapidly decayed once the filament temperature was raised to 1900 "C for Th analysis. Test of Procedure. To test the accuracy and precision on a known Th-U mixture, an aliquot of a 230Th(Oak Ridge National Laboratory) spike solution was mixed with an aliquot of a U500 solution to yield Th and U concentrations of 15 mg/mL and 0.40 mg/mL, respectively. This combined Th and U standard was analyzed six times by the entire procedure, and the results are tabulated in Table 11. The results show excellent agreement between the mean of the measured ratios and the certified ratio, in both cases. The overall precision of the method for both elements was 0.2% RSD. This was the same as the precision of replicate mass spectrometric analyses on a single loading. The above precision and accuracy were within requirements for (Th,U)02fuel isotopic analysis. Isotopic fractionation was often evident during consecutive analyses of a sample; the rate of fractionation varied between 0 and 0.04%/min. This variation was likely a major contributor to the scatter in the results (0.2% RSD). The filament heating and signal measurement technique were repeated as consistently as possible to minimize errors from fractionation.
-
2398
Anal. Chem. 1983,55,2398-2404 i.010
1 L
Oggo
o
i t
0001
001
0 i
i o
io
io0
RC
Flgure 6. Ratio of the isotope ratio (R,) obtained by the bead-disk extraction method to the correspondlng isotope ratio (R,) obtained by a conventional method ( 7 ) vs. the magnitude of the isotope ratio. Samples were irradiated UAI fuels of various enrichments: (0) 2341238;(0)2351238;(A)2361238;( 0 )2351236. Average value of R,IR, is 0.9996 f 0.003. In the above series of analyses, the U concentration was depleted by 30% for numbers 4,5, and 6 (Table 11). The T h concentration did not change significantly, thus the T h to U ratio was 30% higher for the last three analyses. The rate of fractionation did not show a dependence on this change. However, if Th to U ratios that are greatly different from those used in this work are used, the dependence of fractionation on T h to U ratio should be investigated in more detail. For example, in the absence of Th, the U fractionation rate was usually lower; it was usually indiscernible from the normal scatter of the data. A further test of the accuracy of the procedure for U was conducted on a series of UA1 fuels. These fuels were chosen for the test because (a) they represented a fuel matrix for which results could be compared with those obtained by a conventional procedure, (b) they spanned a wide range in isotope ratio, and (c) there was interest in the applicability
of the procedure to uranium fuels. The conventional procedure involved chromatographic separation of U followed by deposition of -30 fig of U on the side filaments (I). The isotopic ratios (R,) obtained by the bead-disk extraction method divided by the corresponding ratios (R,) obtained by the conventional method, are plotted in Figure 6 and show that good agreement was obtained between the two methods. The mean and standard deviation of the ratios of the isotopic ratios are 0.9996 and 0.003, respectively, and are typical of the accuracy and precision of the conventional technique. This demonstrates the applicability of the bead-disk extraction to uranium fuels. Registry No. UOz, 1344-57-6;Al/U, 11149-83-0;U, 7440-61-1; 'W, 13966-29-5;235U,15117-96-1;'W, 13982-70-2;Th, 7440-29-1; 230Th,14269-63-7.
LITERATURE CITED (1) Green, L. W.; Knight, C. H.; Longhurst, T. H.; Crocker, I. H. Report AECL-7686, 1982. (2) Walker, R. L.; Carter, J. A.; Smith, D. H. Anal. Lett. 1981, 14 (A19), 1603- 1612. (3) Smith, D. H.; Carter, J. A. Int. J. Mass Spectrom. Ion f h y s . 1981, 40, 211-215. (4) Faris, J. P.; Buchanan, R. F. Anal. Chem. 1964, 3 6 , 1157-1158. (5) Bruce, F. R., Fletcher, J. M., Hyman, H. H., Katz, J. J., Eds. "Progress in Nuclear Energy, Series 111, Process Chemistry"; Pergamon Press: London, 1956; Voi. 1. (6) Green, L. W.; Knight, C. H.; Longhurst, T. H.; Cassidy, R. M., submitted for publication. (7) Smith, F. J.; Mesmer, R. E.; McTaggart, D. R. J. Inorg. Nucl. Chem. 1981, 43, 541-547. (8) Braun, T.; Ghersini, G. "Extraction Chromatography"; Elsevier Scientific: New York, 1975; Chapter 4. (9) Smith, D. H.; Christie, W. H.; Eby, R. E. Int. J . Mass Spectrom. Ion fhys. 1980, 36, 301-316. (10) Dobretsov, L. N.; Gomoyunova, M. V. "Emission Electronics"; translated by I. Shecktam, Keter Press Binding: Jerusalem, 1971.
RECEIVED for review March 2, 1983. Accepted September 6, 1983.
Characterization of CH,-Homologous Azaarenes in Petroleum by Capillary Gas Chromatography and Mass Spectrometry Gernot Grimmer,* Jurgen Jacob, and Klaus-Werner Naujack Biochemisches Institut fur Umweltcarcinogene, Sieker Landstrasse 19, 2070 Ahrensburg, Federal Republic of Germany
I n Arablan Light about 150 nitrogen-containing polycyclic aromatic compounds of the azaarene fraction were separated by capillary gas chromatography characterized by mass spectrometry and could be attributed to flve CH,-homologous serles. Three of them were ldentlfled as methyl derivatives of 4-azaphenanthrene by comparlson with reference materlals. From the mass spectroscopic fragmentation patterns It may be assumed that the compounds derlve from 4-azaphenanthrene, azapyrene/azafluoranthene, azachrysenelazabenz[a]anthracene/azatrlphenyiene,azabenzopyrenes/azabenzofluoranthenes, and azadlbenzothlophenes, respectlvely. Mass concentrations of these azaarenes per kilogram of petroleum were recorded. The concentration of the main constituents (di- and trlmethyl-4-azaphenanthrene, respectlvely, range from 0.2 to 0.8 mg/kg (in comparison to benzo[a]pyrene, 2.7 mg/kg)).
Polar nitrogen-, sulfur-, and oxygen-containing compounds present in crude oil play an important role in the deactivation
of catalysts. Due to their adsorption on the surface of catalysts they are concentrated in the coke deposits. This is confirmed by the high N/C ratio of the coke layer during hydrotreatment of gas oils containing high concentrations of nitrogen-containing polycyclic aromatic compounds (N-PAC) (1). Apart from this, N-PAC cause instabilities of mineral oil products during storage (2-4). Azaarenes are formed during incomplete combustion or pyrolysis as well as during coalification of nitrogen-containing material and hence they are found in crude oils (5-15, for review see ref 16). A mass spectrometric characterization of polycyclic aromatic hydrocarbons (PAH) and neutral N-PAC (alkylcarbazoles) in a Qatar crude oil has recently been published ( 1 7 ) . Ninety different N-PAC, 41 of which were derivatives of benz[a]- and benz[c]acridine, were tested for carcinogenic effects in animal experiments. Unfortunately, derivatives of benzo[h]quinoline (4-azaphenanthrene) have not been tested for carcinogenicity, whereas quinoline and all of the seven monomethylquinolines were found to be carcinogens (for review see ref 18). Quinoline, all isomeric methylquinolines, and
0003-2700/83/0355-2398$01.50/00 1983 American Chemical Society
