ANALYTICAL CHEMISTRY
936 is more than compensated in many cases by the gain in sensitivity obtained a t 370 mp. For samples requiring the highest accuracy i t has been found advisable to use a wave lengt,h of 400 mp and apply the technique of differential colorimetry. The st’andard deviat’ion expressed as percentage of the mean is about 0.5% for the single extraction procedure and routine colorimetric finish. A sufficient number of samples have not been analyzed by the double extraction procedure followed by differential colorimetry to obtain a reliable measure of the precision to be expected with this method. rlvailable results indicate, however, that the stmanduddeviation expressed as percentage of the mean will be about 0.2%. LITERATURE CITED (1) Cooke,
W. D., Hazel, Fred, and McKabb, W. >I.,
ANAL.
CHEU.,22, 654-5 (1950). (2) Cripps, F. H., Chemical Research Laboratory, Teddington,
Sei. Rept. CRL/AE 73 (1950). (3) Currah, J. E., and Beamish, F. E., ASAL. CHmr., 19, 609-12 (194i). (4) Davenport, \T. H., J r . , and Thomason, P. F., Ibid., 21, 1093-5 (1949). (5) Grimaldi, F. S., and Levine, Harry, U. S. Geol. Survey, A.E.C.D.2824 (1950). (6) Grimaldi, F. S.,May, Irving, and Fletcher, &I. H., C. 9. Geol. Survey, Circ. 199 (1952). (7) Heaney, R. J., and Rodden, C. J., U. 9. Atomic Energy Commission, M.D.D.C.-901 (1946).
(8) Hiskey, C. F., ANAL.CHEM.,21,1440-6 (1949). (9) Hiskey, C. F., Rabinowitz, J., and Young, I. G., I b i d . , 22, 14G4-70 (1950). (10) Kosta, L., BuZZSci. Y u ~ o s l a v .1,41-2 , (1953). (11) Main, A. R., Radioactivity Division, Nines Branch, Dept. (12) (13) (14) (15) (16)
hlines and Technical Surveys, Ottawa, Canada, Topical Rept. TR-111/53 (1953). Mlner, G. W.C., and Smales, A A , , A n a l y s t , 79, 414-24 (1954). lluehlberg, W.L.,I n d . Eng. Cliem., 17, 690-1 (1925). Xeal, W.T. L., Analyst. 79, 403-13 (1954). Rabbitts, F. T., Dept. llines and Technical Surveys, Ottawa, Canada, Mines Branch llemorandum Series 109 (1951). Rabbitts, F. T., e t al., Dept. Nines and Technical Surveys, Ottawa, Canada, RIines Branch AIemorandum Series 105
(1951). (17) Rodden, C. J., “Analytical Chemistry of the Manhattan Project,” XcGraw-Hill, Sew York, 1950. (18) Ryan, W,, and Williams, A. F., A n a l y s t , 77, 293-6 (1952). (19) Yaffe, L., Can. J . Research, 27B, 638-45 (1949). (20) Young, I. G . , and Hiskey. C. F., ASAL. C m x , 23, 506-8 (1951). (21) Zimmerman, J. B., Dept. Mines and Technical Surveys, Ottawa, Canada, Mines Branch Memorandum Series 114 (1951). (22) Zimmerman, 3. B., and Guest, R. J., Radioactivity Division,
Mines Branch, Dept. Mines and Technical Surveys, Ottawa, Canada, Topical Rept. TR-96/52 (1952). (23) Zimmerman, J. B . , Rabbitts, F. T., and Kornelsen, E. D., Dept. hlines and Technical Surveys, Ottawa, Canada, Mines Branch Tech. Paper 6 (1953). RECEIVED for review July 30, 1954. Accepted February 2 , 1955.
Radioisotopic Study of Uranium Separations Separations by Filter-Paper Partition Chromatography with 2-Methyltetrahydrofuran HELEN P. RAAEN and P.
F.
THOMASON
Analytical Chemistry Division, O a k Ridge National Laboratory, O a k Ridge, Tenn.
Radioisotopes were used to study the microseparation of uranium(V1) from 31 metals (32 radioisotopes) by filter-paper partition chromatography with 2-methyltetrahydrofuran. Autoradiography of the chromatograms established the efficiencies of the separations. The sorption gradient of the separated uranium-233 was determined by a-count measurements of the chromatograms; the quantitative removal of approximately 0.3 y of uranium-233 from the paper strip was demonstrated by the same technique. As little as 0.02 y of uranium-233 was chromatographed successfull>-. Braximum condensation of the uranium-233 band was effected by a 1.75-hour elution with watersaturated (at 23” C.) 2-methyltetrahjdrofuran that contained 2.5% (v./v.) concentrated nitric acid. The average Rj value for uranium-233 was 0.95. Of the radioisotopes studied, ruthenium-106-rhodium-I06 and tungsten-I85 were not completely separated from uranium-233. The results for tin-I13 and antimony124 were not conclusive. The behavior of mercury-203 was similar to that of uranium-233.
T
HERE is a general need for a method of separation and
quantitative determination of microgram and submicrogram amounts of uranium(V1). Such a method would find direct use in the analysis of samples of high radioactivity or low uranium concentration. Filter-paper partition chromatography offers a highly satisfactory separation method. According t o Burstall and coworkers ( 7 ) ,the maximum amount of a substance that can be handled successfully by thin filter-paper chromatography is
of the order of 1 mg. The minimum amount depends upon the sensitivity of the technique for the determination of the locus of the sorbed solute and of the method for its estimation, either while it is in place or after it is removed from the paper. The use of radioactive tracers is piobably the most sensitive technique for identifying the locus of a chromatographically resolved substance, being sensitive to as little as a few hundred atoms or molecules ( 1 9 ) . Autoradiography or counting twhniques ( 1 2 ) can be used to indicate the distribution of the resolved radioisotope within its locus. Frierson and Jones (8) used radioactive tracers in paper-partition chromatography of inorganic ions and detected their loci bv autoradiography and counting techniques. HoTvever, uranium(V1) Tvas not among the cations which they studied. Polarography with high-sensitivity instruments (10) may be the most precise method and activation analysis (9) the most sensitive method for the quantitative determination of submicrogram amounts of uranium. These methods are being investigated at this laboratory for the determination of the chromatographically isolated uranium. The method of filter-paper partition chromatography that uses 2-methyltetrahydrofuran for the separation of uranium from other metals was first reported by Arden and coworkers (2). They selectively extracted uranyl nitrate from its solutions by uqe of 2-methyltetrahydrofuran that contained aqueous nitric acid, carrying out the extraction on a strip of absorbent paper. The chromatograms obtained were developed with potassium ferrocyanide reagent, and the uranium was estimated by visual comparison lyith standard stains produced with known quantities of uranyl nitrate. The method was reported to be sensitive to as little as 0.1 y of uranium and semiquantitative for
937
V O L U M E 2 7 , NO. 6, J U N E 1 9 5 5 EXPERIMENTAL TECHNIQUES
Table I.
Radioisotope Identities
0.06 0.1
0.11 ;.11
0.1 0.1 0.0219a 0.436
0.024 0.77
0.0054 0.0251
7
1.75 1.76 1.34 0.1
CS'3'Cl .PrlP'
2.83 0.0006 1.22 0.085 0.01 0.0003 7 x 106 (c.p.m./ml 0.77 0.25 1.06 7
0.1
"03
HSOa Acid b Acid(?)
1:soo
0.886
Sone 1:lOOO I:]
1.7
1: 1000 None 1 : 1000 1: 100 None None
0.1 2.8
HNOi HC1
1:lOO 1:250 1:50 1:50 None ?one
5.9'3
0.1 v.1
HNOa
i .27 -0.1
HNOa "0s HNOa
0 1 0 1 0 1
Preparation of Eluting Solvent. Two procedures were used for preparing the eluting solvent. The first was that of Arden and coworkers ( 2 ) whereby the 2-methyltetrahydrofuran waa saturated with water, then concentrated nitric acid was added to give the desired concentration, and finally more water was added to resaturate the mixture. Because of the possibility of variation in the last step, the procedure was changed slightly. The 2-methyltetrahydrofuran was shaken vigorously with a large escess of water and allowed to remain in contact with the water a t 25" i 2" C. after phase separation. An aliquot of the watersaturated sovent was removed, and the desired amount of concentrated nitric acid pipetted into it, the resulting solution being used as the eluting solvent and also for obtaining an equilibrium atmosphere in the chromatographic cylinder.
1 : 1000 1:20 1: 2000
None 1:250 0,571 1:lOO 1.62 1 : 100 0.1 "03 1:250 0 148 0.1 1:4000 1 80 HKOa 0.1 1:13.2 HNOa 0.549 These are the compounds believed t o have been present in the radioisotope solutions supplied for use in the work and do not necessarily indicate the ionic species existing during the chromatography. b Medium of undiluted radioisotope solutions. 2 2 53 0 125
HNOI HC1 Base HCI
2b 6
0.25 to 200 y with an accuracy of +30%. Lewis and Griffiths ( 1 6 ) extended this Fork and reported the separation of uranium from 52 other metals and its quantitative polarographic determination. However, the description of their experimental work is limited. The work reported here is an application of the radioactive tracer technique, n ith the techniques of autoradiography and a-radiation counting, to the separation of microgram and submicrogram quantities of uranium from other metals b\ filterpaper partition chromatography n ith 2-methvltetrahvdrofuran. It is an extension of the work of Arden and coworkers ( 2 ) and of Levis and Griffiths ( 1 6 ) and supplements their reports with information on the identification of the uranium(V1) locus, the sorption gradient of the uranium, solvent phase separa'ion on the filter-paper strip, aciditv differentials along the strip, effect of the age of the eluting solvent, optimum conditions for isolating and condensing the uranium band on the filter-paper chromatogram, the efficiency of the method for separating uranium from other metal ions, and the quantitative elution of uranium from the chromatogram. RE4GEYTS
Reagents other than those listed were all A.C.S. reagent grade. 2-?\fethyltetrah\-drofuran, Eastman Kodak Co. No. 5971. Filter paper, Whatman No. 1, ashless, 1.5-inch width, roll form. Radioisotopes, described in Table I ; obtzined from Oak Ridge National Laboratory (ORNL) Radioisotope Production L % ~ ~ a l jGroup. ~ses APPARATUS
Chromatography. The apparatus was the type described by Rurqtall and coworkers ( 5 ) . Autoradiography. X-ray film, Kodak medical No-Screen, Eastman Kodak Co , Rochester, K. Y. Dark box, see Figure 1. a Counting. Proportional 01 counter, ORNL Instrument Department, Model Q-721-A. Serial No. 3, or Model IC.
Figure 1. Dark box for autoradiography
Figure 2. Distribution of uranium-233 in chromatogram of 0.1 y of uranium-233(VI) per milliliter of solution
2-Methyltetrahydrofuran reacts extremely vigorously with concentrated nitric acid and great care was required in adding the nitric acid to it. The solvent was placed in an Erlenmeyer flask of considerably greater volume-e.g., a 250-ml. flask for 50 ml. of solvent-and the nitric acid added rapidly to it from a pipet, the tip of the pipet being under the surface of the solvent before nitric acid addition was begun. The solvent was swirled gently during the addition. Experimental reclults indicated that additional purification of the Eaqtman 2-methyltetrahydrofuran was not necessary. Preparation of Chromatograms. A strip of filter paper was cut to a 12- or 14-inch length and usually a 0.75-inch width. A line was embossed lightlv across the strip 3.5 inches from one end, and the strip was folded 2 inches from the same end to facilitate its hanging in the solvent boat. A measured volume of the solution to be tested was delivered from a pipet along this line: the papcr strip TVas held in a horizontal position and care TTYS taken to distribute the solution evenly. Although the solution spread over the width of the strip, no pronounced edge effects xere observed on the chromatograms. The moist spot was airdried. The cylinder and solvent boat ( 5 ) were prepared just prior ta receiving the paper strip. The eluting solvent was added to the
938
ANALYTICAL CHEMISTRY
boat up to a permanent mark a t about half its height. Ten niilli-bother fluorescence method considered was the ashing of liters of the same solvent was plared in the bottom of the cylinder. sections of the chromatogram beneath a sodium fluoride pellet, For some experiments, water was placed in a beaker which rested fusion, and measurement of the fluorescence of the melt by the on the bottom of the cylinder. S o effect from having water vapor fluorophotometer. -4 chromatogram was prepared from 500 piesent was observed. The end of the paper strip nearest the test spot was placed 111 PI. of a solution of 5.0 y of uranium(V1) per milliliter of 0.1M the solvent boat, and the boat and strip placed in the c.dind~.r nitric acid. The fluorophotometric measurement of the uranium so that the strip hung vertically and did not touch the sides of the in segments of the chromatogram indicated a sorption gradient boat or the cylinder wall. The elution was allowed to proceed a t of uranium that terminated abruptly in a section of the chromato25" f 2" C. until the solvent had diffused down the paper sufficiently far to effect a separation. The strip was removed from gram coincident with a narrow dark band of brownish color, the cylinder and allowed to air-dry. .A chromatogram thu8 plcwhich was located about 1 inch behind the solvent front. T h h pared was ready for analysis. h i i d marks the boundary hetiwen tn-o solvent phases that cvist Preparation of Autoradiograms. Autoradiograms of the ( 111 omatograms of the radioisotoDes were prepared by stapling the chromatograms t o sheets of x-ray film, plaring this between sheets of wood pulp, weighting the sheets with a Lucite block, and enclosing the assembly in a special lighttight box (Figure 1). The chromatograms were allowed to remain in contact xith the film for periods ranging from about 16 to 65.5 hours. The minimum time required for the fogging of the film I33 by the chromatographed radioisotopes was not determined. The film was del veloped, and the loci of the radioisotopes ob were determined from the fogging proC ~duced on the film. Measurement of a Counts on Chromatograms of Uranium-233. The chromatograms of uranium-233 were prepared '3 for a-count measurements by cutting the solvent-free chromatogram crosswise into 0.5-inch segments. The counting was done on a proportional a counter a t 52% geometry. Attention was given to constancy of counting conditions. _ - _ - -
-
T i
-
I
RESULTS
Determination of Uranium Locus on Chromatogram with Colorimetric Reagents. The following colorimetric reagents were considered for identification of the uranium locus: potassium ferrocyanide, 8-quinolinol (8-hydroxyquinoline), and ammonium thiocyanate. Sone was sufficiently sensitive to detect microgram quantities of uranium(V1) adsorbed on the filter paper, as indicated by spot tests. The lower limit of sensitivity was found to lie between 1 and 0.1 mg. of uranium(V1) per milliliter of test solution. The 8-quinolinol was the most sensitive reagent, but it formed a yellow color difficult to detect against the yellow color imparted to the paper by the eluting solvent. These results are not in agreement with those of Arden and coworkers (2). F l u o r e s c e n c e Measurement. The work of Sill and Peterson (18) suggested the treatment of the adsorbed uranium(VI) with phosphoric acid followed by visual observation of the enhanced uranium fluorescence under ultraviolet light. Spot tests showed that a spot made with 200 pl. of a solution that contained 1 mg. of uranium(V1) per milliliter of 0.1N nitric acid gave excellent fluorescence after treatment with 25 and 50% phosphoric acid solutions. The test was negative at concentrations of 0.1 mg. of uranium(VI) per milliliter.
P"CMb-;C7iU
Figure 3 . Effect of acid content of eluting solvent on distribution of uraniuni233 in paper chromatogram
ida:tyiTCmv,i
LEVGTH j
,.,e,,
Figure 4. Effect of acid content of eluting solvent on distribution of uranium233 in paper chromatogram
V O L U M E 27, NO. 6, J U N E 1 9 5 5
939
Investigation of Eluting Solvents. Solvents other than 2methyltetrahydrofuran were not investigated because of the extensive work already done on uranium extractants. Optimum Conditions for Separating Uranium by Filter-Paper Partition Chromatography with 2-Methyltetrahydrofuran. Because the combined use of radioisotopes, autoradiography, and radiation counting permits the determination of the loci and distribution therein of chromatographed substances, these techniques are ideal for establishing the optimgm conditions for a chromatographic separation. They were employed in determining the effect on the chromatography of uranium(V1) of the acid content, water content, and age of the eluting solvent and of the elution time. Acid Content of Eluting Solvent. Aronoff ( 3 ) has shown that the sorption gradient of a solute may be a function of the acid content of the solvent, and that the presence of more than one locus may still be identified with a single substance. Since hrden and coworkers ( 2 ) report the use of 2-methyltetrahvdrofuran that contained both 0.25 and 2.5% (v./v.) nitric acid nithout indicating what ac:d concentration is optimum, it was desirable to determine this. Xliquots of 100-p1. volume of a ~ o l u tion that contained 5 y of uranium-233(VI) per milliliter of 0.1S nitric acid were chromatogi aDhed with eluting solvents of watersaturated 2-niethvltetrahydrofuran that contained the following amounts of concentrated nitric acid: 0.25, 0.5, 1.0, 2.0, 2.5, 3.0, 3.5, 4.0, and 5.0 volume %. Elution was allowed to progress approximately 1.5 hours a t 25 O 2 O C. for all the chiomatograms. The acount data for a representative group of these chromatograms are presented graphically in Figures 3 and 4. The results indicate that the optimum nitric acid content of the water-saturated solvent for producing the least trailing of the uranium(V1) band is 2.5% (v./v.). Further increase in nitric acid concentration up to 5y0 (v./v.) did not improve the sharpness of the band. Elution Time. The minimum elution time required to give maximum sharpness of the uranium band when the chromatogram was formed by elution with water-saturated 2-methyltetrahydrofuran that contained 2.5% (v./v.) concentrated nitric acid a t 25" zk l o C. was found t o be 1.76 hours. The data are presented graphically in Figure 5. They show that the sorption zone does not migrate a t a uniform rate, but that the lower portions of the zone, which contain the larger amount of adsorbec' solute, migrate at a slower rate than the upper, a condition also characteristic of some column chromatograms (19). Water Content of Eluting Solvent. No systematic study of the effect of water content of the eluting solvent on the sorption gradient of uranium(V1) was made because a satisfactory condensation of the uranium band was achieved with water-saturated (at 25" f2" C.) 2-methyltetrahydrofuran that contained 2.5% (v./v.) concentrated nitric acid when the elution proceeded for 1.75 hours. Analysis of a represen. tative sample of the eluting solvent for water by the Karl Fischer method gave 49.0, 49.8, and 49.9 mg. per ml. For Figure 5. Effect of elution time on distribution of uranium-233 in paper the purpose of I ough comparison, the chromatogram
the paper s t r i p 4 . e . ) an upper, strongly acidic, and watersaturated phase and a lower, dry-solvent phase that is almost free from acid, as indicated by spraying the chromatogxams with indicator solutions. The brown coloration occurred both in the presence and absence of uranium. The existence of the wet and dry solvent fronts is discussrd below. The fluorescence method v a s of qualitative value only in indicating the distribution of uranium(V1) along the chromatogiam. Use of Uranium-233, Autoradiography, and 01 Counting. The inadequacy of colorimetric methods and the slowness of the fluorophotometric procedure in detecting the locus of natural uranium on the cnhromatogram led to the substitution of the sadioactive isotope, uranium-233 (specific activity = 2.1 X 10'O disintegration per minute per gram), for natural uranium in the study of the sorption gradient of uranium on the Chromatogram. Autoradiograms and a-count measurements of the uranium-233 chromatograms were mad(.. The sorption gradient of uranium233 in the chromatograms wits indicatpd by both techniques for a qolution that contained 1.0 y of uranium-233(VI) per milliliter. The counting technique w s the more sensitive. This is shown 111 Figure 2 , in which the a-count data are presented graphically tor a chromatogram of a solution of 0.1 y of uranium-233(VI) per milliliter. S o autoradiogram of this chromatogram was detectahle even after it had been in contact with the x-ray film for ahout G5 hours 011
{
ANALYTICAL CHEMISTRY
940
-
I
59
z "233
"$33
"233
/ N
P
$33
+
Fe55 59
$33
+
itoradiograms of ohromatograms showing separation of uranium-233 from the radioisotope indicated
\" ',
? "
se75
"e33
+
"93
'
+
"233
idiograms of chromatograms showing separation of uranium-233 from the radioisotope indicated
V O L U M E 27, N O . 6, J U N E 1 9 5 5 values of Bennett and Philip ( 4 ) for the percentages (weight) of water in 2-methyltetrahydrofuran (no nitric acid present) a t the temperatures indicated follow: Water in 2-JIet hyltetrahydrofuran Temp., 0 C. wt.70" &lg./ml. 6 .15 7.03 60.8 20 6.65 57.4 25 52.4 6.08 a Bennett and Philip data ( 4 ) b Calculated from Bennett and Philip data by use of 0.8625 gram per ml. a s density of 2-methyltetrahydrofuran.
941 The quantitative determination of submicrogram amounts of uranium on the chromatogram by activation analysis and in the eluate by high-sensitivity polarography is currently being studied.
-_
Age of Eluting Solvent. When concentrated nitric acid is added to water-saturated 2-methyltetrahyd~ofurana t room temperature and in the manner described above, the reaction ib vigorous, and the solution undergoes an immediate color change from almost colorless to yellow. On standing (approximately 1 hour), the solution becomes deep reddish brown, Tvhich fades until the solution is again yellow. The nature of the reaction is not known. This color change suggested experiments with eluting solvents of different ages. 0-Count data from experiments with 10-minute and 1-hour-old eluting solvents indicated that the uranium-233 sorption giadient is less n-ith the older solvent; this factor warrants further study. Separation of Uranium(V1) from Other Metals. Studies with Radioisotopes. The effectiveness of the separation of uranium from 31 other metals (32 radioisotopes) by filter-paper partition chromatography with 2-niethyltetrahj drofuran under the optimum conditions described above was studied with radioisotopes. The number of metals tested \\as limited by the availahility of the radioisotopes. The chi oniatograms TT ere prepared according to the procedure given above. Separate chromatograms were prepared for a blank of ieagents, uranium-233(VI), the other radioizotope, and uraniuni-233(VI) plus the other radioisotope. I n the last case, the two radioisotopes were applied to the paper strip in separate solutions, the strip being air-dried after each deposition The loci of the uranium-233 and other radioisotope bands were determined by autoradiography, and the sorption gradient of the uranium-233 by 01 counting as described above. The method of measuring the Rrvslues is subject to variation and require- s o n e explanation. I n the case of the uranium-233, the distance moved by the band vias considered t o be the distance betlveen the line on which the solution was applied and the center of the uranium233 hand (alnays coincident mith the wet-solvent front). The distance nioiTed by the dry-solvent front was that fr0.n the same line to a line that marked thc farthest advance of the dr\-solvent front. Thus: distance moved by uranium-233 band, em. Rffor uranium-233 = __ distance moved by dry-solvent front, em. For radioisotopes that shoned diffuse bands, R, values were estimated only roughly or not a t all. An R, value of zero indicates no movement of the band, and a value of 1.00 indicates movement of the metal in the dry-solvent front. The results of the separation studies are given in detail in Tahle 11. Positive prints of the autoradiograms are given iii Figures 6 through 9. Consideration of the band rvidth is essential to the proper interpretation of band resolution. Quantitative Removal of Uranium from Filter-Paper Strip. Quantitative removal of the uranium was achieved by elution. Each paper strip 1\89 cut to a 9-inch length and tapered to a point along the lower 3.25 inches. The uranium was chromatographed as described above. The minimum time required for the removal of uranium was determined by use of uranium-233 and measurement of the residual LY counts on the chromatograms after various elution times. The data showed that quantitative removal of 0.5 y of uranium-233 is achieved if the elution proceeds, under the conditions designated above, for a minimum of 1.73 hours after the front of the uranium-233 band (wet-solvent front) reaches the end of the strip.
DISCUSSION
Mechanism. Xccording to Arden and coworkers (1, 2 ) and Burstall and coworkers ( 7 ) , the factors that cause separation of inorganic salts by partition chromatography on rellulose may be: selective extraction of the salts by the organic solvent, partition of the inorganic substances between organic solvent and aqueous layer, adsorption of metallic ions by the paper, and the formation of complexes with high solubility in organic media. Pollard and coworkers ( 1 7 ) likewise suggest that one of the main factors in paper chromatography of inorganic compounds is the distribution of the compounds between the organic solvent and Tvater. That the first two factors are the major ones that cause theseparation of uranium(T1) when uranyl nitrate is eluted on filter paper Fvith 2-methyltetrahydrofuran that contains aqueous nitric acid is indicated by the study of extractants for uranium and by the work of Burstall and coworkers ( 5 ) . They suggested that those inorganic salts which have a high solubility in organic solvents tend t o be extracted in the solvent front and t o form bands narrower than the original spot. This behavior rvas observed consistently for uranium-233(VI). The formation of wet and dry zones and of an acid gradient on the paper strip was observed in the course of this study.
Table 11. Separation Behavior of Uranium-233 and Other Radioisotopesa Radioisotopeb
Band Width, Cm. czd RadioU233 isotope
... ..,
... ... ...
...
... ...
...
(b:i0) (11.5) (6)
...
...
(19:O)
(13:O) (7.0)
(6.0)
Resolved into three bands (1.3)
o'io
0.05 0.05 0.15 0.10 0.30
..
0 : io 0.15 0.40 0.20 0.15 0.10 0.10 0.10 0.12 0.12 0.70 0.50 0.20
... ...
Resolbed into several bands
!
$
0.04 0 0.03 0 01 0 0
$2
? 0.98 0
(? 6.5
...
!
0.3 0.1 5 0.6 0.2 0.2 0 15 0.1
(i:&0 (6.6)
Ri Valuee Behavior Radioof L-233 isotope Radioisotopef .. 0.95Q 0 0.45 0 0 95 0 0.95 1 .. 2 0 0:94 I 0.95 1 0.94 Q 0.96 ... 0 1 0.94 ? 2 0.95 ? 0 97 3 7 2 0.96 a 1 0.98 0 1 0.95 1 0.96 2 0.95 0.96 1 (0.99) 2 0.22 0.95 2 2 0.01 0.97 ? 0.95 1,3,4
0.20
0.96 0.97 0.95 0 95 0 94 0 97 0.95 0.96
2 1
2 2
1 1 1 1,2,3,4
!.96
0.96 By filter-paper partition chromatography r\-ith nater-saturated 2-methyltetrahydrofuran t h a t contained 2 . 5 % ( v . / v . ) concentrated nitric acid. b Radioisotope other t h a n U233. See Tahle I for a complete description. C Band width covered b y the aliquot of radioisotope solution, on application t o the filter uaper strip, v a s -6.0 cm. for the -100-pl. aliquot, and -1.5 cm. for the -5-MI. aliquot. d Approximately 100 pl. of the radioisotope solution was used except in the case of the Xln% Sh124, Te125, Ta'82, and Hg2o3 solutions of which approximately 5 pl. was used. cm. traveled by radioisotope e R~ = cm. traveled by dry-solvent front f Exact behavior of each radioisotope in the presence of U233 is indicated by its autoradiogram. Figures 6 through 9. Behavior in the absenceof the uranium was the same in each case, therefore those autoradiograms are not shown. The general behavior is indicated by one of the following statements: (1) N o movement from test spot. (2) Partial movement from test spot. (3) Complete movement from test spot: hand diffused. (4) Complete movement from test spot: hand condensed. 0 Average value determined from 29 chromatograms. a
.
ANALYTICAL CHEMISTRY
942
Figure 8. Prim
These conditions are discussed below, an explanation tor which has been proposed by Burstall and coworkers ( 5 ) . Separation of Phases on Filter-Paper Strip. The water-saturated 2-methyltetrahydrofuran that contains nitric acid undergoes & frontal analysis as i t passes along the paper strip-Le., it changes composition as it moves away from the bulk of the solvent that is contained in the boat. The composition change results from the sorption of water by the cellulose until an equilibrium is reached and a dry-solvent front moves ahead of the wet-solvent front. The nitric acid undergoes partition between the water in the cellulose and that in the solvent, and an acid gradient is formed in the wet phase, the dry phase being only slightly acidic. The mechanism far the formation of the two phases and the partition of acid hetween them has been postulated by Burstall and coworkers (6) for the 1-butan~l-hydrochloric acid-water eluting solvent system. Similar behavior was found for the 2-methyltetrahydrofurrtn-nitric acid-water system. The acid differential in the aqueous phase wm identified by spraying the chromatograms with Bin indicator solution. The existence of two solvent fronts on paper-strip chromatograms has also been shown by other workers for the l-butanol-hydrochloric acid-water (16) and the propyl ketonehydrochloric acid-water ( 6 ) systems. A so-called "brawn front" (11) marked the advancing edge of the wet phase, both in the presence and absence of added metal ions. It was especially useful in indicating the uranium-233 band, which was always coincident with it. This coloration a t the wet-solvent fmnt has been described for both nonacidic and acidic systems-i.e., collidine-water (If) and l-butanol-hydrochloric acid (16). The nature of i t is not known. DSerential Migration of Uranium. The differential migration of uranium-233 along the paper strip is indicated by the e-count data of Figure 5. Theprocess by which this differential migration
take8 place is suggested by Kowkabany and b a s a a y ( 1 1 j - ~ e . , the eluting solvent "operates as a moving vehicle which transports solute from the rear to the front of a zone.'' R,,Values. Ri values are influenced by a variety of factors and should not be interpreted without full consideration of the experimental conditions. Kowkabany and Cassidy (11)have described Some factors that affect Rj values as determined by experiments with amino acids a8 solutes. Distance of the initial spot from the surface of the eluting solvent and time of elution both affected R, values, whereas the following factors were reported to have had little effect: amount of solute being eluted, rate of flow of eluting solvent, temperature, long "equilibration," prewashing of the filter paper with the eluting solvent, and prefiltration of the eluting solvent through the paper. From this information, some generdiarttions can be made far inorganic ehromatography. Burstall and coworkers (6) have described other factors that affect R, values of inorganic solutes. For the ealculation of the RIvdues given herein, the distance of travel of the dry-solvent front was preferred t o that of the wet-solvent front because the dry-solvent front was always marked by the termination of the yellow color of the paper over which the solvent moved, therefore w a easy to identify, and because certain solutes moved beyond the wet-solvent front. The reproducibility of the R j values for uranium-233, when experimental Conditions are held constant, is indicated by the data of Table 11. Under these same experimental conditions, the R ~ v a l u ecould be used for the identification of uranium in an unknown. Band Width. Consideration of band width together with the Ri value is essential to the proper interpretation of the paper chromatographic separation of a solute. The width of the umnium-233 band is shown by the data. herein to be a function of the acid and water contents of the eluting solvent, of elution time,
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Figure9. Prints of aut