620
Anal. Chern. 1980,
V shows ratio data ( E 200 n m / E 206 nm) of some pure amino acids determined with the variable wavelength detector. For pure arginine and the corresponding peak in orange juice, the equivalent ratios of 3.32 and 3.25, respectively, were found. CONCLUSION T h e method developed for aualitv and stabilitv tests can be used to analyze intravenous solutions quantitatively in unattended operation when an automatic sampling system is used. No sample preparation is required. T h e repeatability of the retention time was found to be within *0.8% relative standard deviation, the quantitative repeatability was within 2.2% relative standard deviation for all amino acids except T h r (4% relative standard deviation). Under the same chromatographic conditions, vitamins niacinamide, B2,B6,and C present in the intravenous solutions can be quantitated. T h e investigations have shown that the same method can be useful in the analysis of beverages like orange juice, wine, and beer. Similar chromatographic conditions should be
52,620-624
applicable also for the analysis of peptide- and protein-hydrolysates in the food industry and in biomedical research.
ACKNOWLEDGMENT The author thanks Manfred Riedmann for helpful comments and encouragement.
LITERATURE CITED (1) Zimmermann, C. C.; Appella, E.; Pisano, J. J. Anal. Biochem. 1977, 77, 569. (2) Jamabe, Takeo; Takei, Nobluam; Nakurma, Hirashi. J Chromatogr. 1975, 104, 359. (3) Beyer, H.; Schenk, U. J . Chromatogr. 1969, 89, 483. i4) Lin, Jen-Kun; Change, Jin-Joe. Anal. Chem. 1975, 4 7 , 1634. (5) Moore, S.;Stein, W. H. J . Biol. Chem. 1954, 277, 907. (6) Harmeyer, J.; Salimans, H. P.; Ayoub, L. J . Chromatogr. 1968, 32, 259. (7) Voelter, W.; Zech. K. J . Chromatogr. 1975, 112, 643. (8) Schuster, Rainer "HPLC in Pharmaceutical Products: Vitamins", Hewlett-Packard GmbH, Boblingen. GFR, 5953-0026.
RECEIVED for review August 23, 1979. Accepted January 15, 1980.
Determination of Plutonium in Soil by Gas Chromatographic Separation and a Spectroscopy Falko Dienstbach and Knut Bachmann" Fachbereich Anorganische Chemie und Kernchernie, Technische Hochschule Darrnstadt, D-6 100 Darmstadt, Germany
An analytical procedure for the determination of plutonium in soil samples is given. By this procedure, the sample is decomposed completely by hydrogen fluoride. The hydrogen fluoride is evaporated and the residue is chlorlnated. Plutonium is separated from the sample by volatilization and separation of the chlorides in the gas phase. The plutonium is deposited on a glass disk by condensation of volatilized plutonium chlorlde. The concentration of plutonium is then determined by a spectroscopy.
Analytical methods reported in the literature for the determination of plutonium in environmental samples are based on separation of plutonium from sample material by coprecipitation and extraction ( I ) or by ion exchange ( 2 ) and subsequent electrodeposition of the plutonium for N counting. At nuclear power plants, a great number of analyses of plutonium in environmental samples have to be carried out for safety controls. I t therefore seems desirable to carry out the plutonium analyses automatically. Common analytical methods for the determination of plutonium are not quite suited for automatization. Therefore we have developed an analytical procedure which is based on volatilization and gas chromatographic separation since these methods are suited for automatization and probably allow the separation of plutonium and americium simultaneously. Gas chromatographic separations of plutonium from different elements have been reported by several groups. Zvarova and Zvara (3) separated trace amounts of transuranium elements using gas chromatography of gascous complexes of aluminum chloride with transuranium chlorides. 0003-2700/8@/0352-062@$01 00 '0
Tranikov et al. ( 4 ) separated microgram amounts of plutonium from milligram amounts of rare earths by gas adsorption chromatography of their gaseous chlorides, and Merinis et al. ( 5 )separated trace amounts of different actinide chlorides by gas adsorption chromatography. Jouniaux (6) investigated the behavior of the fluorides of plutonium and of other transuranium elements under gas adsorption chromatographic conditions. Naumann (7) separated plutonium from uranium by gas chromatographic separation of the chlorides on graphite. The main difference between our procedure and the above mentioned methods is the fact that for separation of plutonium from soil, trace amounts of plutonium have t o be separated from weighable amounts of a number of elements while by the reported separations only trace amounts were separated from each other or plutonium was separated from one single element.
EXPERIMENTAL Evaporation of Plutonium Chloride from Soil. The experiments were carried out using a simple apparatus which consisted of a quartz tube with an outer diameter of 20 mm and a length of 70 cm. In this tube a condensation tube could be placed. The region of constant temperature in the 50-cm long furnace was about 40 cm. Two grams of a sandy soil which had been ashed at 550 "C and spiked with 50 pCi 239Pu/gwas placed in the middle of the furnace and heated in a stream of Cl2/CCI4 gas. The volatilized products were deposited in a Condensation tube. X-ray fluorescence analysis was carried out on the soil, the condensed chlorides, and the remaining residue (Figure I). The plutonium concentration of the residue was determined by a procedure given by Schuttelkopf (I). Separation by Sublimation of the Chloride Using Different Chlorinating Gases. The apparatus consisted of a quartz c 1980 American Chernical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 4, APRIL 1980 n\
Cc Ci
MnFe Fe
Ca
Fz Fe Z r
5r Zr
a)
621
N2
1
AlCl PbClZ
N2
I
a1 AlCl 7 1160"Cl
Flgure 3. Separation procedure for the separation of plutonium from
soil using AICI, as carrier gas: (a) volatilization of the chlorides and transport with AICI,, (b) separation of the chlorides by sublimation at different temperatures 3 had a negative temperature gradient of 6 K/cm; and furnace 4 with a length of 50 cm, had a constant temperature zone of 40 cm. The sandy soil was spiked with 3 pCi 242Pu,0.15 pCi *,'PU, and 0.36 pCi 238Puper gram. A 2-g sample was dissolved in HF, heated to 70 "C, the H F evaporated, and the residue dissolved in HNO, HC104, evaporated to dryness, and then dissolved in HC1 and evaporated to dryness again. The residue was placed in the separation tube (Figure 3) in furnace 2. The sample was then volatilized in a gas flow of Clz/CC14which was saturated with A1C13 at 150 "C. The vapor pressure of AlC13was regulated with furnace 1. A1C13was passed through furnace 3 and part of it was condensed at the beginning of furnace 4 and the rest in the condensation tube. The furnaces were held a t the following temperatures: Furnace I: 150 "C; furnace 2: 900 "C; furnace 3: a gradient from 650 "C down to 350 "C; and furnace 4: the first 10 cm at 130 "C and the rest a t 160 "C. The temperature of the nozzle was always 100 "C higher than that of furnace 4,so as to avoid any deposition. The gas flow rate was 2 L / h C12/CC14;the duration of the volatilization was 3 h. At this step of the separation, plutonium was deposited at the beginning of furnace 4 together with PbC12, MnCl,, AlCl,, and FeC1, whereas the alkaline chlorides were deposited in furnace 3 at ca. 550 "C. This could be shown by X-ray fluorescence analysis. TiC14and part of FeCl, which is transported with the A1C13, is deposited in the condensation tube. At the second step of the separation, furnace 4 was heated up using a temperature program, while the other furnaces were shut off. Argon was used as the carrier gas with a flow rate of 4 L/h. The temperature of furnace 4 was increased to 160 "C and held a t this temperature until the A1C13had been completely evaporated. This step took about 1 h. Then the temperature was elevated to 200 "C and held there for 0.5 h, in order to volatilize the FeC1, completely. Then the temperature was increased rapidly to 550 "C and PbC12 evaporated. During this step the beginning of furnace 4 was heated up to 600 "C. After PbC1, had been volatilized out of the separation tube, the condensation tube was shifted toward the condensation disk. Instead of argon, now C1, was used as the carrier gas, with a flow rate of ca. 1.2 L/h. Under these conditions PuC1, was formed, volatilized, and condensed at the glass disk. This step took about 0.5 h. The amount of plutonium was determined using semiconductor detectors with an active diameter of 20 mm. The distance to the N plate was 3 mm. The diameter of the area of the electrodeposited plutonium was 8 mm, so that the counting efficiency was 32%. The vapor-deposited plutonium was distributed on a larger area on the disk. Therefore the counting efficiency was only 18%, as found by comparison with 2~-a-counting.
+
RESULTS AND DISCUSSION T h e separation of P u from soil by gas phase separation is in principle divided into 2 steps: (1)the volatilization of P u out of soil and (2) the separation of plutonium chloride from other chlorides.
622
ANALYTICAL CHEMISTRY, VOL. 52, NO. 4, APRIL 1980
*-
MOOO
Figure 4. Volatilization of plutonium out of soil as a function of time ( t ) at 1000 OC;gas flow, 2 L/h CI,/CCI,
t
T. "C bl
loo0 Bx)
lo0
50 % Pu in the residue
Figure 5. Volatilization of plutonium out of soil as a function of the reaction temperature (T); gas flow, 2 L/h CI,/CCI,; duration, 3 h
Evaporation of Plutonium Chloride from Soil. In order t o separate or to preconcentrate plutonium from soil, it is necessary to convert the plutonium oxide, which is probably the main species in soil, into a compound which is volatile under 1000 OC. Therefore we investigated the optimum conditions for volatilization of Pu using spiked 239Pu(200 pCi). T h e optimum conditions for the volatilization were obtained by variation of the time (Figure 4) and of the temperature (Figure 5 ) for the volatilization. The duration for the volatilization should be at least 4 h and the temperature between 700 and 1000 OC. T h e highest temperature which could be reached with the quartz tube was 1100 "C. At this temperature, the silicates of the soil are sintering together and the plutonium is dissolved in the silicates, so that the yield decreases, as is demonstrated in Figure 5. Together with plutonium, a great number of other elements are volatilized as chlorides, e.g., K, Ti, Mn, Fe, Cu, Zn, Pb, and R b (these are elements which are easily detected in soils with X-ray fluorescence) as is shown in Figure 1. As expected, all oxides which are chlorinated using C12/CC14are volatilized when the vapor pressure of their chlorides or oxide chlorides is high enough. From the sandy soil, about 10% of the weight evaporated. In order to determine by N spectroscopy, it was necessary to have a thin layer of less than 50 Fg/cm2 produced after the separation. Therefore from a 2-g sample, 200 mg of volatile compounds could be expected, from which P u had to be separated together with no more than 50 Fg of interfering chlorides. Separation by Sublimation of Chlorides Using Different Chlorinating Gases. A temperature programmed sublimation was carried out, since at least 2-g samples had to be used, which is too much for a n isothermal gas chromatographic separation. In this first step, plutonium should be evaporated in a certain temperature range and preconcentrated. We used three different reactive gases (C12,HC1, and CCl,). By changing the chlorinating agent, either the formation of PuC1, was favored (Clz as reactive gas) or the
Ii -
-
Fec'3
t I
*"I I i L
OJ 100
J
L
Jl-----
700 900 T'C Figure 6. (a) Sublimation of chlorides as a function of temperature ( T ) using N2/CCI, as reactive gas, (b) sublimation of chlorides as a function of temperature ( T ) using C12/CCI, as reactive gas,(c)sublimation of chlorides as a function of temperature ( r ) using HCI as reactive gas 302
500
formation of PuCl, (HC1). When N2/CC1, was used as reactive gas a t lower temperatures, only PuCI3 is formed whereas a t higher temperatures PuC1, is also formed, depending on the dissociation of CC14 In Figure 6 the amourits (arbitrary units)
ANALYTICAL CHEMISTRY, VOL. 52, NO. 4, APRIL 1980
are plotted vs. the temperature. Figure 6a shows that when N2/CC14is used as reactive gas, plutonium chloride is volatilized together with part of the PbC12 between 450 and 500 "C. When Cl2/CC1, is used, plutonium is volatilized together with FeC1, (Figure 6b) between 150 and 300 "C. The experiment in which HC1 was used (Figure 6c) showed that plutonium is not volatilized at all a t temperatures lower than 920 "C. The experiments show that the type of reactive gas does not influence the volatilization of the chlorides of Zn, P b , Rb, and Ti, but the choice of the reactive gas is important for the volatilization of plutonium chloride. T h e volatilization temperatures found by these experiments corresponds to a vapor pressure of 0.1 to 1 Torr (8). This value depends on experimental conditions, such as heating rate, gas flow, and tube length. Fe forms FeC1, and FeC1,. The broadening of the Fe peak is the result of the evaporation of FeC1, at about 200 "C; of the reaction of part of the remaining FeC12 above 550 "C to form FeCl,, which is volatilized; and finally of the evaporation of the FeC12 a t high temperatures. As already mentioned, plutonium was found in t h e FeC1, fraction when C12 was used as the carrier gas, whereas it was found in the PbC12fraction when N2/CC13was used. Plutonium chloride exists in the solid state as PuCl,, and i t may exist as PuCl, in the gaseous state only in the presence of Cl, (9). This explains why no PuC1, is formed when HC1 is used as the reactive gas. The vapor pressure of PuC13, ca. 0.1 Torr a t 930 "C (8) is too low a t temperatures lower than 920 "C to elute the plutonium out of the separation tube. In a N2/CC14 atmosphere, the partial pressure of C12 at 500 "C is high enough to form PuC1, which has a vapor pressure of about 0.1 Torr a t 500 "C in a chlorine atmosphere (9). This is perhaps not the only reason why PuC1, is eluted together with PbC1, in a N,/CCl, atmosphere. Schafer ( I O ) has found that ThC1, a n d PbC14 form gas phase complexes. In the same way PuC1, should react with PbC1, and since the vapor pressures are approximately in the same range at this temperature, this means that it is not easy to separate PuC1, from a greater amount of PbC12 in the presence of chlorine. T h e volatilization of PuCl, together with FeCl,, in a C1, atmosphere can be explained by the existence of FeCl3~,)-PuCl4 gaseous complexes. Similar complexes are mentioned in the literature (11). PuCl, should form a gaseous complex with FeC1, too, similar to the NdCl,-AlCl,~,) complex (12),but the stability of this complex is less than the stability of the PuCl,-FeCl,(,, complex, due to the higher heat of vaporization of PuC1, compared with that of PuCl,, and consequently PuCl, is not transported out of the residue. The chemical properties of PuC1, and PuC1, allow different approaches to the gas phase separation of plutonium from soil: (a) Separation of plutonium together with FeC1, under a chlorine atmosphere, and then separation from FeC1, with N2 or HC1 gas. (b) Separation of FeCl, from the soil using N2/CC14,then separation of plutonium together with PbC12,followed by the separation of P u from PbC12 with N, or HC1 gas. (c) Separation of the volatilized products from the remaining PuCl, with HCl and thereafter volatilization of PuCl, with C12. Of these 3 possibilities, the first one has been investigated thoroughly. S e p a r a t i o n of P l u t o n i u m f r o m Soil by T r a n s p o r t of the Chlorides with Gaseous AlC1,. Usually the yield of the separation of 239/240Pu is determined by addition of 236Puor 242Puas spike. When 236Puor 242Puis added to the solid soil, it is possible that it behaves different chemically from the "naturally" occurring P u during the volatilization step. The direct volatilization from soil corresponds to the leaching by the usual separation technique, a procedure which is quite
1
,
,
35
L
dj' 1 , % 239 PL(:~ 4 5
keL
c5
623
,
1
6 iWV1
Figure 7. cy spectrum of vapordeposited plutonium chloride containing 3.6 pCi 242Pu,0.18 pCi 239Pu, and 0.43 pCi 23BPu
controversial (13). T o avoid this risk the ashed solid was completely decomposed with HF. T h e separation was then carried out according to the method explained in detail in the Experimental section, where the plutonium chloride is volatilized out of the residue forming a complex with FeC13. T o increase the transport effect and to avoid any dependence on the concentration of Fe in the soil, AlCl, was passed over the sample simultaneously to the volatilization. AlCl, was used instead of FeC1, since it normally exists only in one valence state. The use of AlCl, is less complicated than that of FeCl,, because i t is completely sublimated a t low temperatures in contrast to FeCl,, which may decompose to FeC12. Another reason for using AlC1, is that at a given temperature the vapor pressure of AlCl, in equilibrium with solid A1Cl3 is higher than that of FeCl,, so AlC1, is sublimated a t lower temperatures than FeCl,, which prevents losses of plutonium since the transport rate increases with increasing temperature. Using AICl, a number of other chlorides were also transported, but these chlorides could be separated a t step 2 of the separation. T h e chemical yield which could be obtained was maximum ca. 60% of the 6 pCi of %?u, which had been added as spike. Figure 7 shows an a spectra of a vapor-deposited plutonium sample. The peaks of the different plutonium isotopes are clearly separated. T h e ratio of 23sPuand 239Pu to 242Pucorresponds to the ratio of the added spike. T h e detection limit which we have obtained to date is 20 fCi/g soil, with a counting time of 16 h, with the detection limit for our given detector arrangement assumed to be 10 imp/l6 h. There are several explanations for the chemical yield of 60%: (1) The volatilization has been incomplete. The reasons may be too short a volatilization time and/or reaction with the quartz tube. This may be improved by changing the experimental conditions. (2) With the deposition of the alkaline chlorides, plutonium chloride is co-deposited. A lower temperature gradient a t furnace 3 should be advantageous. The alkaline chlorides are deposited on a larger area and the diffusion of the co-deposited plutonium through the alkaline chloride may be favored. (3) The evaporation of plutonium chloride from furnace 4 (Figure 3) has been incomplete. This could be improved by using higher temperatures and by coating the quartz surface, in order to avoid reactions of plutonium chloride with the quartz. (4)The volatilized plutonium chloride is not completely deposited at the glass disk. The deposition yield could be increased by optimization of the deposition conditions, such as the gas flow rate, the diameter of the nozzle, and the distance from the nozzle to the deposition plate. ( 5 ) AlC1, might transport the plutonium chloride out of the separation tube. This can be prevented by depositing all of the AlC1, in furnace 4,and not evaporating the AlCl, before the C12 has been shut off. The time needed for the separation
Anal. Chem. 1980, 52, 624-630
624
temperature to 900 "C in furnace 4 (Figure 3) a t step 2 of the separation procedure. However, neither the yield nor the thickness of the deposited layer of 241Amwas satisfactory, so that modifications of the procedure will be necessary. Interferences of neodymium found by Knab (14) subsequent to ion-exchange separations of americium from soil might be overcome, since a separation of Am and Nd in the gas phase should be possible (15).
is then increased of course. T h e separation technique has until now been tested only on sandy soils, so it is an open question whether this technique could be used for all kinds of environmental samples, or whether the procedure would have to be modified. But the results show in any case that it is possible to separate picogram amounts of plutonium from gram amounts of soil by gas chromatography, as long as it is possible to obtain CY plates by simple vapor deposition of nearly the same quality as those made by electrodeposition. The time needed for the analysis is almost the same for the gas chromatographic analysis as for the classical analysis. The detection limit applied to a 2-g sample is somewhat better for the classical analysis, because of the better yield of 80% compared with 60% and the higher counting rate of 32% compared with 1870,but since the detection limit is still low enough for environmental control analysis, this is not a serious drawback for the gas chromatographic analysis. An advantage is the simple control for memory effects. For this control, the separation tube has simply to be heated up to 800 "C for 1 h, while a stream of C1, is passed through, until no plutonium is condensed on the glass disk. Only the HF decomposition device remains as a source of contamination, and this may easily be controlled separately, while for the classical analysis the whole separation procedure has to be carried out in order to control for memory effects. T h e gas chromatographic analysis may be run automatically with only slight modifications. The end of the separation tube has to be split into 2 outlets, one for A1C13. FeCI,, and Pl)Cl> and the second in connection with a capillary for the condensation. T h e gas chromatographic separation method is probably also suitable for the determination of americium in soil. Preliminary experiments where the soil sample wa5 spiked with 100 pCi 241Am/ghave shown. that A m CY plates could be obtained by vapor deposition only by increasing the
ACKNOWLEDGMENT The authors thank M. Pimpl, who participated in the early steps of the volatilization experiments. LITERATURE CITED Schuttelkopf, H. "Rapid Methods for Measuring Radioactivity in the Environment", Proc. IAEA, Vienna, 1971, 183-200. Chu, N. J. Anal. Chem. 1971, 43, 449-452. Zvarova, T. S.,Zvara, I. J . Chromatogr. 1970, 4 9 , 290-292. Travnikov, S. S.; Davydov, A. V.; Myasoedov, 0 . F. Radiochern. Radioanal. Lett. 1976, 2 4 , 281-289. Merinis, I.; Legaux, Y.; Bouissieres, G. Radiochem. Radioanal. Lett 1970, 3 , 255-261. Jouniaux. 6.Thesis, University Pierre and Marie Curie, Paris, 1979, Naumann. D. Kernenergie 1963, 6 , 116-121. Kubaschewski, 0.;Alcock, C. B. "Metallurgical Thermochemistry", 5th ed.; Pergamon Press: Oxford, 1979. Keller C. "The Chemistry of the Transuranium Elements"; Verbg Chemie: Weinheim. Germany, 1971; p 374. Binnewies, M.; Schafer, H. Z . Anorg. AUgern. Chem. 1974, 4 7 0 , 149- 155. Schafer, H. Angew. Chem. 1976, 88, 775-789. Gruen, D. M.; @a, H. A . Inorg. Nucl. Chem. Lett. 1967, 3 , 453-455. Sill. C. W.; Puphal, K. W.; Hindman. F. D. Anal. Chern. 1974, 46, 1725-1 737. Knab, D. Anal. Chem. 1979, 57, 1095-1097. Steidl, G . ; Bachmann, K. Technical University, Darmstadt, Germany, private communication, 1979.
R E C E I ~for ~ I review I September 28, 1979. Accepted December 10, 1979. The authors are grateful to the "Bundesministerium fur Forschung und Technologie'' for their financial support.
Determination of Ionization Constants by Chromatography Darawan Palalikit and John H. Block" School of Pharmacy, Oregon State University, Corvailis, Oregon 9733 7
termination of the ionization constant of a compound. Each method has its advantages and disadvantages. The spectrophotometric method requires chromophores which absorb ultraviolet or visible light. Also the relevant ionic and molecular species must have different spectra. The potentiometric titration method is very commonly used, but good water-solubility with an adequate quantity of the compound is needed. The conductometric method is quite tedious and more time consuming. The proton magnetic resonance method has proved useful for substances whose ultraviolet spectra do not change upon ionization, but the compound must be water-soluble. T h e limitations of the proton magnetic resonance method are the types of buffer that must be used, and the fact that a t least one proton must show a significant chemical shift when going from the unionized to the ionized species. All of these four methods require a compound which i. very pure. An alternative approach is to use chromatography Advantages of this method are that (1) small quantities of compounds are required; ( 2 ) poor water-solubility need not
The determination of the pK,'s of several organic acids and bases using chromatography was investigated. Normal-phase buffer-impregnated paper chromatography was found to be unsuitable. TLC plates impregnated with mineral oil were examined as a possible reversed-phase method, with poor results. The use of XAD-2 copolymer as the stationary phase In a simple HPLC method gave good results. Experimentally determined pK, values were confirmed using UV spectrophotometry with the identical solvents and buffers used in the HPLC method. Statistlcal comparisons using both pK, and K, values were performed. The advantage of using a computer method involving the second derivative to determine pK, is illustrated.
Several experimental methods sucli as ~VectrcJi)lic,tometry ( I ) , poteritiometry (2), conductornetry ( ; j ) , and p r o t n r i magnetic resonance spectrometry (2, 4 ) are available for the deC1003-2700,83/3357-0624$0 1 O O / O
L
1980 American Chemical Society
