Table I. Quantitative Separation of Zirconium from Hafnium Amount of Zr and Hf taken in the mixture, mg Hf Zr Hf Zr found, found, error error Zr Hf mg mg 2.34 0.91 2.32 0.91 0.0 +o. 02 4.60 0.0 1.82 -0.04 1.82 4.64 2.32 -0.04 0.00 3.60 3.64 2.32 $0.02 0.00 0.464 0.93 0.91 0.464 0.92 1.81 -0.01 -0.01 1.82 0.93 1.78 1.43 1.82 1.39 -0.04 +0.04 2.70 1.82 1.82 2.78 0.0 +0.02 3.70 1.82 3.75 1.81 -0.05 -0.01 0.26 1.82 0.24 1.83 $0.01 +o. 02 1.81 1.82 2.43 0.00 -0.01 2.43
The plot of log Kd us. Concentration of formic acid given in Figure 1 is very interesting. It appears that hafnium forms a positively charged stable complex with formic acid at concentrations from 0.25-1.75M and, therefore, in these concentrations the Kd values are very high and almost constant. However, in case of Zr it appears that two complexes are formed with formic acid in this range. First a positively charged complex is formed at 0.75M, and there is a n increase in Kd value up to 1.OM. When the concentration of formic acid is increased further, an uncharged complex is formed and, hence, the Kd value falls abruptly. The reactions involved may tentatively be postulated as follows:
+ HCOOH ZrO(HC00)+ + H + Z r O ( H C 0 0 ) + + HCOOH ZrO(HC00)2 + H + Zr02+
+
+
by evaporation and hafnium content was determined chelometrically. It was ascertained by loading the column with halfnium solution and eluting with formic acid that hafnium was completely retained in the column. The results are given in Table I.
(2)
When the concentration of formic acid is increased further, Hf shows a decrease in the Kd value after 10.OMformic acid. At this concentration, there is probably a formation of uncharged Hf complex-Le., HfO (HC00)2. The bimodal behavior shown by zirconium in 4.OM-20.OM formic acid is probably due to adsorption and not to ion exchange.
DISCUSSION AND RESULTS It is clear from the results that formic acid offers an exceedingly favorable separation factor for the separation of these two elements. We have demonstrated the importance of the method by choosing the less favorable concentration of formic acid-i.e., 1.OM. At this concentration, the separation factor is about 40 and the separation is easily achieved. In more favorable cases, the separation factor is still greater-i.e. > 100 and better separations should be possible.
ACKNOWLEDGMENT The authors are thankful to Dr. S.M.F. Rahman for providing research facilities. RECEIVED for review July 6, 1970. Accepted October 8, 1970. One of us (K. H.) extends his heartfelt gratefulness to C.S.I.R. India, New Delhi, for providing financial assistance.
Plutonium Determination in Soil by Leaching and Ion-Exchange Separation Norton Y. Chu Health and Safety Laboratory, U . S. Atomic Energy Commission, New York, N . Y . 10014
DURING MAY1969 a fire occurred at the Dow Chemical Company’s Rocky Flats, Colo., facility where plutonium components for nuclear weapons are fabricated. After the accident, many soil samples were taken in the immediate and outlying vicinity of the facility to determine the extent of the radioactive contamination. This report describes the methods used at the Health and Safety Laboratory (HASL) to determine the levels of plutonium in 100 gram samples of soil. Over a number of years plutonium analyses (1-8) have been (1) Health and Safety Laboratory Manual of Standard Procedures, J. H. Harley, Ed., U. S. At. Energy Comm. NYO-4700, Rev.
1970. (2) H. Levine and A. Lamanna, Health Phys., 11, 117-125 (1965). (3) P. J. Magno, P. E. Kauffman, and B. Schleien, ibid., 13, 13251330 (1967). (4) E. E. Campbell and W . D. Moss, ibid., 11, 737-742 (1965). (5) K. Wolfsberg, W. R. Daniels, G. P. Ford, and E. T. Hitchcock, Nuel. Appl., 3, 375-377 (1967). (6) M. C. deBortoli, ANAL.CHEM., 39, 375-377 (1967). (7) K. C. Pillai, R. C. Smith, and T. R. Folsom, Nature, 203, 568-571 (1964). (8) E. L. Geiger, Health Phys., 1,405-408 (1959).
performed on different biological and environmental samples for monitoring purposes. These samples include air, food, water, excreta, fused rock, and soil. Several authors have used anion exchange systems to isolate plutonium from complex matrices (9-1 I ) . The ion-exchange separation scheme used here was suggested by the investigations of Kressin and Waterbury (IO). Plutonium has been measured in 1-10 grams of soil and while this is adequate when the plutonium concentrations are sufficiently high, such small sample sizes may prevent plutonium detection when the levels are low. Except for deBortoli (6), the analysis for plutonium has not been made routinely on 100 grams of soil although plutonium and other actinides have been measured on kilograms of fused rock (5). For the analysis of the Colorado soils, it seemed desirable to analyze a minimum 100-gram (9) D. B. James, Los Alamos Scientific Laboratory Rep., TID-4500, January 1967. 34, 1598(10) I. K. Kressin and G. R. Waterbury, ANAL. CHEM., 1601 (1962). (11) R. F. Buchanan, J. P. Farris, K. A. Orlandini, and T. P. Hughes, U.S.At. Energy Rep., TID-7560, 1958, p 179. ANALYTICAL CHEMISTRY, VOL. 43, NO. 3, MARCH 1971
449
sample since a wide range of plutonium concentrations was expected. Briefly, the method consists of leaching soil with a mixture of nitric and hydrochloric acids in the presence of z a 6 P ~ tracer. After leaching, plutonium in the leachate is converted t o PuCIv)with sodium nitrite and absorbed from 8 N nitric acid onto Dowex 1-X4 ion exchange resin. The major constituents of the sample pass through the resin. Plutonium is removed from the exchanger with a mixture of dilute nitric and hydrofluoric acids and finally electroplated on a platinum disk from slightly acid ammonium chloride solution which is sufficient to prevent hydrolysis. The plated disk is counted on an alpha spectrometer. Identification of the plutonium isotopes in the sample is made by comparison of the sample spectrum with a n electrodeposited standard source. The results obtained by leaching were found to be in good agreement with plutonium measurements of reference soils analyzed a t HASL by complete solution of the sample. EXPERIMEh'TAL
Reagents and Apparatus. All reagents used in the chemical method are of analytical grade; standardized plutonium-236 N tracer solution-about 10 dpm/gram; 0.4N "03-0.01 HF solution; 0.1% methyl red indicator solution; 5 % sodium nitrite solution, freshly prepared ; analytical grade Dowex 1-X4 (100-200 mesh) resin, Bio-Rad type A G ; Platinum disks, 17.6-mm diameter X 0.005 in., one side mirror finished; Nickel disks, 17.6-mm diameter; electrolytic cell; electrolytic analyzer; and large and small ion-exchange colums. Resin Preparation. About 15 ml of Bio-Rad A G 1-X4 (100-200 mesh) resin are used for each sample and are prepared as needed by conversion from chloride to the nitrate form with 1 :1 nitric acid. Prolonged storage of the resin in high nitric acid concentrations will promote degradation. Column I Preparation. The column is made from borosilicate glass. The outside diameter is 17 mm with a reservoir at the top of the column (35-mm diameter and 75 mm lohg) and a glass stopcock at the lower end. The overall length of the column is 315 mm. Fill the column to the reservoir with 1 :1 nitric acid and position a plug of glass wool at the base. Transfer 5 ml of resin to the column with 1 : 1 nitric acid. Column I1 Preparation. The column is made from borosilicate glass. Dimensions are the same except that the outside diameter is 11 mm. Prepare column I1 in the same way as column I, except add 2 ml of resin. Electrodeposition Apparatus. The electrodeposition of plutonium is carried out in a cell (2) based on numerous other designs. It consists of a n elongated 22-mm cap which holds a 1-oz polyethylene bottle with the bottom removed. The cap has space for an 18-mm diameter platinum plating disk and a nickel backing disk and may be screwed firmly into the polyethylene bottle forming a leak-tight plating cell. A threaded brass bushing is molded into the cap and allows electrical contact to be made with the platinum disk cathode by clip leads. The cell may be supported in the ice-water bath with a clamp stand; our cell is supported on a Lucite pedestal which makes it easier to center the anode stirrer. The anode is a 1it6-in. platinum-iridium rod 4 inches long with a half inch diameter platinum disk riveted at one end. The disk has a number of '/*-in. holes cut into it to lighten the stirrer. It is connected through a variable speed (50 to 500 rpm) stirrer to the positive outlet of the electroanalyzer. A Power Designs transistorized power supply (Model 2015R) furnishes a constant current ranging from 0-1.5 amperes and a constant voltage ranging from 0-20 volts. It is connected in parallel with an "Elaviscript 3" chart recorder which plots voltage os. time at constant current during elect rodeposition. 450
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Sample Preparation. Complete details of the sampling procedure for the Colorado soils are given by Krey and Hardy (22) and are similar to those used for soil sampling at the Health and Safety Laboratory ( I ) . The air-dried weight of the samples collected averaged about 20 kilograms. Associated rock and vegetation from the sample were separately crushed, ground, and blended, then combined with the soil and the whole blended again. The sample was quartered and about a kilogram of the material taken at random. The kilogram sample was further pulverized and blended so that 100-gram aliquots could be taken for analysis. Chemical Method. Weigh 100 grams of the prepared soil sample into a 1-liter beaker and add a known amount (-3 dpm) of plutonium-236 tracer. Add slowly 300 ml of nitric acid. Foaming may be prevented by adding a few drops of n-octyl alcohol. After the reaction has subsided, add 100 ml of hydrochloric acid. Allow the mixture to react at room temperature for an hour; then boil for an hour while stirring. Cool to room temperature. Decant the liquid into another 1 -liter beaker and reserve. Repeat the nitric-hydrochloric acid leach for another hour with stirring and boiling, and cool to room temperature. Decant, combine the liquid with the reserved solution and evaporate to about 200 ml. If siliceous material is present, dilute with an equal volume of water and filter, then wash the residue with dilute nitric acid. Reserve the filtrate. Transfer the filter and residue to a platinum crucible and ignite. Cool, add hydrofluoric and nitric acids, and evaporate to dryness. Add nitric acid and evaporate again to dryness. Dissolve the residue in nitric acid and combine with the reserved filtrate. Adjust the solution to 8N in nitric acid. Ion-Exchange Procedure. Heat the 8N nitric acid sample solution to 90 "C and add 2 ml of freshly prepared 5% sodium nitrite solution. Cool in an ice-water bath to room temperature. Add 5 ml of the conditioned ion-exchange resin to the sample and stir for 5 minutes. Transfer the sample and the resin to column I . Allow the solution to flow through the resin bed at full flow until the liquid level reaches the top of the resin, Discard the effluent. Elute plutonium with 150 ml of 0.4N HNO,-O.OlN HF. Discard the resin. Evaporate the solution to dryness and convert the residue to nitrate by twice adding 5 ml of nitric acid and evaporating to dryness. Dissolve the residue with 15 ml of 1 : 1 nitric acid and heat to 90 OC. Add 0.25 ml of 5 % sodium nitrite and cool to room temperature in a n ice-water bath. Add 2 ml of the conditioned resin to the solution and stir for 5 minutes. Transfer the sample and resin with 1 :1 nitric acid to column I1 and allow the solution to flow through the resin bed at full flow until the liquid level reaches the top of the resin. Wash the resin with 15 ml of 12N hydrochloric acid, three 10-ml portions of 1: 1 nitric acid and discard the effluent and washings. Elute plutonium with 100 ml of 0.4N HN03-0.01N HF. Discard the resin. Evaporate the solution to dryness and convert the residue to chloride by adding 1 ml of hydrochloric acid twice and evaporating to dryness after each addition. Electroplating Procedure. The electroplating is largely based on the procedure described by Mitchell (23). Add 1 ml of hydrochloric acid to the dried plutonium residue and heat gently. Transfer the solution with a transfer pipet to the electrolytic cell. Wash the beaker and pipet with two 1-ml portions of water and combine the sample in the cell. Add 1 drop of methyl red indicator and adjust the pH to just basic with ammonium hydroxide. Make the solution just acid with 1:5 hydrochloric acid and add 2 drops in excess. Dilute to 5 ml with water. Electroplate at a current of 1.2 amperes for 1 hour. Quench the electrolyte with 1 ml of ammonium hydroxide at the end of the electroplating period. Dismantle the cell and rinse the platinum disk with water then (12) P. W. Krey and E. P. Hardy, Jr., U. S. A I . Etiergy Rep., HASL-235, Aug. 1970. (13) R. F. Mitchell, ANAL.CHEM., 32, 326-328 (1960).
DISCUSSION AND RESULTS
Table I. Plutonium Recovery from Soil Leached with NitricHydrochloric Acids and Separated by Ion Exchange Analysis No.
Added
dpm 236Pu Found
1 2 3 4 5 6 7 8 9 10
1.84 1.86 1.94 1.95 2.12 2.13 2.13 2.18 2.19 2.55
1.43 1.46 1.64 1.63 1.71 1.97 1.96 1.94 1.82 2.10
Chemical yield, Z 77.8 78.5 84.5 83.6 80.7 92.5 92.0 89.0 83.1 82.4
Table 11. Comparison of Plutonium Analysis in Soil by Nitric-Hydrochloric Acid Leach and Sodium Carbonate Fusion Methods Sample number 1A 1B 2A 2B 3A 3B
Method Leach Fusion Leach Fusion Leach Fusion
$39, 240
dr)m/100 g __ PU 238Pu
308 i 11 318 =t12 1629 i 87 1607 i 82 6.0 f0.2 8.0 f 0.3
5.9 f 0.2 6.6 f0.3 32 i 2 35 f 2 0.19 f 0.01 0.13 f 0.01
Chemical vield.
Z 53 59 56 66 58 61
ethanol. Flame the disk to red heat over a burner to convert plutonium to the oxide. Assay the disk o n the alpha spectrometer and resolve the plutonium isotopes. Standardization. An electrodeposited standard source containing 236Pu, 241Am,and *44Cmis measured in the alpha spectrometer system. The spectrum supplies a calibration curve of alpha energy cs. channel number as well as the detection efficiency of the system. Measurement of individual electrodeposited standard sources of 236Pu,241Am,and 244Cm shows that the detection efficiency is independent of alpha energy over the energy range of interest.
A n effort was made t o shorten existing separation and collection procedures for removing plutonium from complex matrices. Classical methods used t o remove minute quantities of plutonium from the bulk of the sample, such as phosphate collection, solvent extraction, o r rare earth fluoride scavenging, could be omitted for a n experimental soil sample. Plutonium was removed from the leachate of the soil by ion exchange. A resin bed with a height less than 5 cm for column I operation where the sample volume averaged about 300 ml tended to lose plutonium because of the amount of wash solution necessary to remove extraneous ions. The final purification step of plutonium on column I1 required a minimum 5 cm in height resin bed to satisfactorily retain plutonium. The ion-exchange column sizes used in this work were available in this laboratory and used as a matter of convenience. The experimental samples shown in Table I were collected in a n area of New York where the soil type is a fine silt loam. Also, Table I gives the amounts of plutonium-236 tracer recovered from two ion-exchange passes of the soil leachate from ten 100-gram aliquots of the experimental samples. The recovery of plutonium-236 tracer ranged from 78 t o 93 %. Duplicate 100-gram aliquots of three soil types were selected from samples taken from various locations in the Colorado area. The samples, 0-20 cm, from this area were generally sandy loam and mixed with rock and vegetation as described previously. One aliquot was analyzed by the nitric-hydrochloric acid leach method and the other by complete solution of the soil using sodium carbonate fusion. The plutonium-239 240 and plutonium-238 values obtained by the two methods are shown in Table 11. The overall chemical yield of the plutonium-236 tracer ranged from 53 to 66%. We believed in this early work the reason these chemical yields were lower than those of our experimental soil samples was probably because of mineral variations. Since that time further analyses have shown that the chemical yields obtained at HASL by the leach method have improved and range between 78-86%. It is shown from the measurements in Table I1 that good agreement was obtained between
+
Table 111. Interlaboratory Comparison Analysis of Plutonium in Soil. Sample location Colorado 1
a
Laboratory A HASL HASL A HASL HASL A HASL HASL
Method HNOI-HCI leach HN03-HCI leach Na2C03fusion Colorado 2 "03-HCI leach "03-HCI leach Na2C03fusion Colorado 3 HNOI-HC1 leach HNOa-HCI leach Na2C03fusion Illinois 1 B HNO3-HCI leach HASL NA2C03leach New York 1 A HN03-HCl leach HASL NA2CO3fusion New York 2 B HN03-HCI leach B HF dissolution B H F dissolution HASL Na2C03fusion New York 3 B HNO3-HCI leach B H F dissolution B H F dissolution HASL "01-HCI leach Error term for all measurements is a single Poisson error due to counting.
400i 4 308 i 11 318 f 12 1600 i 33 1629 f 87 1607 i 82 10.2 i 0 . 2 6.0 f 0.2 8.0 f 0.3 0.74 It 0.25 0.51 f 0.03 1.7 f 0.1 1 . 7 f 0.1 0.41 i 0.07 0.35 i 0 . 1 5 0.49 i 0.07 0.41 f 0.02 4.82 i 0.23 4.58 i 0.25 4.49 i 0.24 4.13 f 0.17
7.2 i0 . 2 5.9 f 0 . 2 6.6 i0.3 31.8 i 1 . 3 31.8 f 2 . 0 37.3 i 1 . 6 0.20 f 0.03 0.20 i 0.01 0.13 i 0.01
...
...
0.04 i 0.01 0.41 i 0.02 0 . 2 7 f 0.21 0.09 f 0.18 0.04 i 0.04 0.03 f 0.02 0.03 f 0.03 0.20 i 0.10 0.14 i 0 . 0 9 0.32 i 0.02
ANALYTICAL CHEMISTRY, VOL. 43, NO. 3, MARCH 1971
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the shorter leaching method and the more lengthy sodium carbonate fusion dissolution method. Since a large number of sample analyses were necessary to evaluate the extent of plutonium radioactivity in the Colorado area, commercial laboratories were asked to assist in this work. They were requested to analyze the soils by the nitric-hydrochloric acid leach and t o compare this method with their internal methods. The results of the intercomparison are shown in Table 111. The error term shown for all measurements is a single Poisson error due t o counting. Measurements from Laboratory A for the Colorado soils in two out of three cases show higher plutonium-239 240 results than the measurements at HASL. A systematic error was not found for this difference. The sample collected in Illinois is a glacial silt “black” soil and this type has been used in this laboratory as a reference soil. The New York soils, 1, 2, and 3, also silt loam, were collected at a different site than the experimental sample; soil 1 was collected in 1967 from 0-20 centimeters and soils 2 and 3 were collected
+
____
-
__
__--
in 1969 a t 5-20 and 0-5 centimeters, respectively. Except for New York sample 3 which was 50 grams, all soils in Table 111 were analyzed using 100 grams. From the plutonium 239 240 results shown, the leaching method is comparable to other methods for the determination of plutonium in soil containing fresh and aged fallout. Also, from these results, it was concluded that either of the methods tested would be adequate for plutonium soil analysis although the nitric-hydrochloric acid leach method required one third the analysis time as compared to the method of complete solution by sodium carbonate fusion. A more detailed interpretation of the results obtained from Colorado soils as well as the extent of plutonium contamination found in the Rocky Flats area has been made by Krey and Hardy (12).
+
RECEIVED for review September 1,1970. Accepted November 10,1970.
~
Isothermal Gas Chromatographic Separation of Carbon Dioxide, Carbon Oxysulfide, Hydrogen Sulfide, Carbon Disulfide, and Sulfur Dioxide Willis L. Thornsberry, Jr. Research and Deceloptnent Laboratory, Freeport Sulpliur Company, Belle C l i m e , La. 70037
THEREHAS BEEN a persistent need for a simple and rapid method for analyzing mixtures of CO,, HIS, SO,, COS, and CS2. The importance of such a method has been greatly magnified by the increased emphasis placed on monitoring the concentration of these components in waste gas streams. Although the procedure described here is not applicable t o concentrations below the 50-ppm concentration range, it is useful for the monitoring of gases emitted from sulfuric acid plants, Claus recovery units, and for various other process control and laboratory applications. Recent papers by Stevens et a/. ( I , 2) describe a gas chromatographic system for the analysis of some sulfur gases in the concentration range extending below 1 ppm using a 34-ft Teflon (Du Pont) column containing 40-60 mesh Teflon packing coated with polyphenyl ether and phosphoric acid. A sulfur selective flame photoluminescent detector was used in this study. In the past ten years, a number of papers have been published which are concerned with the development of gas chromatographic columns for the separation and analysis of sulfur gases. Several of these papers were discussed in a previous communication from this laboratory (3). Since that time other methods have been published. Brinkmann ( 4 ) discussed the development of a column for the separation of these five gases; however, the method is hampered by a tailing SO2 ____~~_____.____
peak and the fact that no base-line separation is obtained either between COSand the inert gases, or between H S and COS. The development of porous polymer beads has provided what is probably the best and most trouble-free method for separating these gases when carbon disulfide is not present (5, 6). A 6-ft x 1/An, aluminum column of Porapak Q-S was tested in this laboratory and COS, COS, H2S, and SOY were eluted within 6 minutes; however, a CSn peak was not observed until about 40 minutes after sample injection. The column temperature was 98 “C and the helium carrier gas flow rate was 5 5 cc/min. An earlier communication from this laboratory outlined an analytical procedure for the simultaneous, isothermal separation and analysis of CO,, COS, H2S, SO2, and CS? using a silica gel column (3). Since that time, numerous columns have been prepared from this same batch of silica gel. All of these columns have been used successfully both in the laboratory and (with the addition of a precut column to remove moisture) in process instruments for continuous analysis. However, attempts to reproduce these results with silica gel from other sources and even with different lots obtained from the same source have failed. Various methods of treating these silica gels have been tried, including silanizing ; acid washing, using conditions ranging from simple washing t o refluxing with concentrated hydrochloric acid for 2 to 3 hours; and conditioning the
( 1 ) R . K. Stevens e/ a/., E/iriro/i.Sri. Tec/ino/., 3, 652 (1969). (2) R . K. Stevens and A . E. O’Keeffe, ANAL.CHEM., 42, (2), 143A (1 970). (3) C. T. Hodges and R . F. Matson, ihid., 37, 1065 (1965). (4) H. Brinkmann, C/iem, T c ~ / i(Leipzig), . 17, 168 (1965).
( 5 ) E. L. Obermiller and G. 0. Charlier, J . Gas Clzromatogr., 6 , 446, (1 968). (6) E. L. Obermiller and G. 0. Charlier, J . Chromatogr. Sci., 1, 580 (1969).
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