using silica gel support bound with starch, since starch bound supports will tolerate up to 1.0 pg. of resorcinol before tailing becomes a problem. Spray reagents other than the iodinestarch were used but iodine-starch was preferred. A 0.1% solution of silver nitrate in methanol was also used for detection. Resorcinol turned black with the silver nitrate spray. A precision study was made for resorcinol in which six standards containing0.05, 0.1, 0.2,0.4, 0.8, and 1.Opg. were placed on each of seven plates. The areas were determined as described earlier. The relative standard deviation
was 3.98% for resorcinol in this weight range. The methods were considered accurate for the determination of nitroglycerin and resorcinol in semimicro and micro propellant samples. Other propellant components ,did not affect the determination of nitroglycerin and resorcinol, provided the same solvent was used for standard and sample. If nitrocotton content was very high, which would affect the determination of both compounds, the sample had to be diluted. This method can be extended to larger samples if proper care is taken in dilution.
LITERATURE CITED
(1) Aurenge, J., DeGorges, M., Normand, J., Bull. SOC. Chim. France 1963, 1732. (2) Becker, W. W., Shaefer, W. E., “Organic Analysis,” Vol. 11, p. 101, Interscience, New York, 1954. (3) Bobbit, ,!. M., “Thin Layer Chromatography, p. 117, Reinhold, New York, 1963. (4) Purdy, S. J., Truter, E. V., Lab. Pract. 13. 500 (1964). ( 5 ) Seher, A., Die Nahrung 4, 466 (1960). (6) Stahl, E., Chemiker Ztg. 82, 323 (1958). J. A. KOHLBECH
Hercules Powder Co. Bacchus Works Magna, Utah
Rare Earths Separation by Anion Exchange Chromatography in Salt Solution Magnesium Nitrate Medium
SIR: Rare earths do not adsorb to any great extent on the strong base anion exchanger from mineral acid solutions. A suggested approach to increase the adsorption of the rare earths with anion exchanger is use of media of low acid with high salting strength. Danon (2) showed that praseodymium absorbs more strongly on Dowex 1 from nitrate solutions than from the acid media and that the adsorption of praseodymium increases with the nature of the cation of the supporting nitrate solution in the order H < iKH4< Li< Ca < Cu < Fe < Al. Marcus and Nelson ( 7 ) investigated the adsorption of several lighter rare earths in LiN03 solution with a strong base anion exchanger. Sufficient differences in adsorbabilities permitted the separation of the lighter rare earths a t an elevated temperature. The measurement of distribution coefficients was also extended for the heavier lanthanides (6). Buchanan and Faris ( I ) reported that considerable fractionation of the rare earths occurred in 10-1.1 “,NO3 solution of low acidity. The distribution coefficients on Dowex 1-XI0 decreased with increasing atomic number ranging from 100 for La to approximately 4 for Lu. However, considerable overlapping of elution bands a t room temperature resulted in a column elution with the highly cross-linked resin. No further detailed information is available. It should be recognized that the nitrate does not always cause the pronounced adsorption of rare earths regardless of the nature of the cation concerned and that the effect of the nature of cation on the separation factor has not been clarified. Therefore,
hLa
t
a
I
I
1
CONCN.
I
I
OF
Mg(NOJ2
1
1
3
2
M.
Figure 1. Variation of Kd with concentration of Mg(N03)2solution containing 0.005M free nitric acid Resin, Dowex 1 -XE, NOa-form
it appeared to warrant more extensive investigation of the possible utilization of anion exchange resin in a salt solution for the separation of rare earths, The present work centered on the adsorption study of the rare earths from Mg(NO& solution, and provides a
useful procedure for the rare earth separation. EXPERIMENTAL
Apparatus and Reagents. ION EXCHANGE RESIN. Strong base-type anion exchange resin, Dowex 1-X8, VOL. 37, NO. 10, SEPTEMBER 1965
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NO3-form, in a particle size of 200- t o 400-mesh was used. The commercial resin of analytical grade, C1-form, was converted to NOS-form and stored in a large desiccator containing saturated KBr solution. IONEXCHANGE COLUMN. Conventional ion exchange columns of 0.54-cm. i d . , pulled to a tip, and plugged with glass wool a t the outlet of the column were generally used. Dried resin (6.4 grams) was slurried with water and poured into the columns. The resulting bed height was approximately 50 cm. long. Shorter columns of the same i d . , with 2.0 grams of resin weight and 16 cm. of bed height, were also used for the determination of distribution coefficient. STOCK SOLUTION AND TRACERS. d stock solution of each rare earth was prepared by dissolving appropriate amounts of its oxide (99.9yo purity) into 331 " 0 3 , evaporating to dryness, and diluting with 0.1JP " 0 , to a definite volume. The solutions were standardized by titration with 0.001JP EDTA solution using xylenol orange as indicator. Radioactive tracers, Lala (40 hours), Pr142(19.2 hours), and Gd159 (18.0 hours) were produced by irradiating the respective oxide of spectral purity with neutrons in the reactor a t St. Paul's University, Yokosuka. The irradiated oxides were processed in the same way as used for the preparation of stock solutions. Ce144 (285 days) and ELI'S' (16 years) were obtained through a supplier and found to be of satisfactory purity by half-life measurements or separate column experiments. All of the other chemicals were of analytical grade, unless otherwise mentioned. All of the experiments were performed using the radioactive tracers with or without carriers, and with resin loadings of less than 1% capacity. Measurement of Distribution Coefficient, Kd. The weight distribution coefficient was measured either by a batch equilibrium method (4) or by column elution method ( 5 ) according to the order of magnitude of the distribution coefficient. Usually the Kd values greater than 20 were measured by the batch method. Column Separation. Pretreat the column before use with sufficient magnesium nitrate solution to be used as eluent. Evaporate a sample solution containing a pair of rare earth elements, each spiked by respective radioactive tracer. Take up the residue into 1 to 2 ml. of magnesium nitrate solution of a desired concentration, adjusted to 0.005M in free nitric acid. The concentration of magnesium nitrate may vary according to the pair to be separated. Allow the solution t o pass down the column at a flow rate of 1 ml. per 15 minutes. When the sample solution reaches almost the top of the resin bed, start the elution with the same magnesium nitrate solution as used for sample preparation a t the flow rate of 1 ml. per 6 minutes. Collect successively 1- to 5-ml. fractions of the effluent in polyethylene vials, and take the activity measurement with the aid of a standard well-type 1284
ANALYTICAL CHEMISTRY
I
\
. I .
I
\
21-
30
4 O V 20
-
20
"10
k N
10
0
(e)
-
50
40
30
60"
0.5MHN03
x
5-
75 125 150 V O L U M E O F E F F L U E N T , ml. Figure 2.
175
Examples of a typical separation of a mixture of rare earths ( a ) Eu carrier-free, N d 300 pg. a d d e d (b) Pr 160 pg,, La 30 pg. a d d e d IC) Sm 5 pg., N d 1000 pg. a d d e d (d) Pm carrier-free, N d 200 pg, a d d e d (e) Eu carrier-free, Sm 10 pg. a d d e d
gamma scintillation counter. Identify the rare earths corresponding to particular maxima of the elution curve by decay rate measurement and y-ray spectrometry or by separate column experiments. RESULTS AND DISCUSSION
The adsorption of rare earths from magnesium nitrate solution depends to some extent on the free acid concentration. Actually, in 2.65X Pvlg(NO3)~ solution the distribution coefficients of La and Pr do not change so markedly in the concentration range of " 0 8 , 0.1 down to 0.005.11. On going to higher acid concentration the adsorption of both elements decreases more rapidly with increasing acid concentration. In a similar manner the separation factor, ::aJ as defined by Kd(La)/ Kd(Pr), decreases rapidly on going to higher concentration of "03, ranging
from 2.8 for 0.00551 acid down to 1.6 for 2M acid. The effect of acidity on the adsorption seems to be more serious in Lih'o3 media, where the acid-independent region appears a t much lower acidity of 10-*31 to 10-4M "03 (7). A series of adsorption measurements was taken as a function of J f g ( N 0 3 ) ~ concentration with solutions containing 0.005.U free nitric acid. The results are quoted in Figure 1 for the lighter rare earths ranging from La to Gd. A value for Pm was obtained from a elution profile curve for the separation of Pm*49 (52 hours) from neutron irradiated neodymium, which is shown later in Figure 2. The distribution coefficients of some of the heavier rare earths were briefly reported before, together with those for Sc, Th, and U in 3M Mg(N03)2solution, giving 12 for Tb, 13 for Dy, 14 for Ho, and 17 for Lu (3). So far as the behavior of rare earths in 331 Mg(N03)2 solution is
concerned, the distribution coefficient decreases montonically, reaching a minimum a t Gd, and then increases slightly with increasing atomic number ( 3 ) . The slope d log K d / d M Mg(NO& decreases with increasing atomic number within the lighter rare earths. Therefore, one can expect the best fractionation of this group to occur in Mg(N03)2solution of the highest molarity, although limited to ‘V 1.7). The practically 3M separation factor of an adjacent pair of the lighter rare earths in 3 to 4M LiN03 was reported by Marcus and Kelson (Y), who gave B : l ~ Y 1.4. In Mg(N03)2 medium, :,CY a t 2M Mg(NOJ2 (equivalent in formality to 4M LiN03) comes out to be -1.5. Therefore, the separation factor of the rare earths in nitrate media appears to be independent of the nature of cations concerned, although the adsorption (Kd) varies considerably with the nature of cation, as demonstrated for Pr by Danon (2). The results given in Figure 1 should
permit the selection of an optimum condition for a given rare earths separation. With the anion exchanger-Mg(NO& system, good separation of the rare earths would be expected in the Mg(N03)Z solution of the highest concentration. I n Figure 2 the results of a typical separation of a mixture of the rare earths are shown. Because of the rather difficult separations involved, elution of the element to be removed first should be as sharp as possible so that the peak spreading is kept minimal. This is possible by decreasing the concentration of eluent a t the obvious sacrifice of the separation factor. The separation of a mixture of the rare earths, which differs in the atomic number by 2 or 3, is satisfactory as shown in the separation of E u and Nd, Pr and La, and Sm and Nd in Figure 2. However, the separation of adjacent pairs of the rare earths-Le., Pm-Nd and Eu-Sm-is less satisfactory using the conditions selected.
LITERATURE CITED
(1) Buchanan, R. F., Faris, J. P., Intern. At. Energy Agency, Vienna, Conf. Proc. 2. 262 f 1962\.
(1964). ( 5 ) Hamaguchi, H., Ohuchi, A., Onuma, Tu’., Kuroda, R., J . Chromatog. 16, 396 (1964). (6j-Ma;cus, Y., Abrahamer, J. Znorg. Nucl. Chem. 22,141 (1961). (7) Marcus, Y., Nelson, F., J . Phys. Chem. 63, 77 (1959). HIROSHI HAMAGUCHI~ KOJIISHIDA IKUKO HIKAWA ROKURO KURODA
Department of Chemistry Tokyo Kyoiku University Bunkyo-ku, Tokyo, Japan 1 Present address, Department of Chemistry, The University of Tokyo, Hongo,
Tokyo, Japan.
Estimation of Vanadium in Biological Material by Neutron Activation Ana lysis SIR: Activation analysis is a rapid and sensitive technique for the detection of vanadium in biological material. The main problem is the completion of an efficient separation within the time limit set by the rapid decay of the radioactive vanadium ( t l / s = 3.8 minutes). The initial destruction of the organic matrix is a step which consumes a considerable amount of time in rapid analytical procedures. This is especially true with hard tissues such as bone or tooth, where a destruction time of 10 to 20 minutes is often required, even when vigorous conditions are used (1, 3 ) . The following method allows counting of the separated vanadium within 8 to 10 minutes of removal from the reactor. Naturally occurring vanadium is 99.76% V51, which on irradiation with thermal neutrons produces V2. The cross-section for thermal neutrons is 4.5 barns and the V52 half-life is 3.8 minutes. Both p and y radiations are emitted, but detection by Geiger counting is preferred because of comparatively low background of this type of counter. There is the possibility of interference by the following first-order reactions: Cr52 (n, p ) V52 Mn55(n, CY) V6* These are only significant in matrices with high chromium or manganese
content and do not require a correction factor in biological materials. The radioactive tissue sample is destroyed in boiling sulfuric acid and the heavily charred solution is cleared by addition of nitrate. After scavenging and solvent extraction with cupferron, the vanadium cupferrate is counted in a Geiger counter accepting liquid samples, diluted to a standard volume, and its absorbance is measured. EXPERIMENTAL A N D RESULTS
Preparation of Samples. Tissue samples are vacuum-dried and receive no treatment before irradiation so t h a t contamination is kept t o a minimum. With hard tissue such as tooth, sections are used as obtained from a cutter, after rinsing with distilled water. The cutter is carefully protected against contamination. I t is necessary to investigate the cutting wheels to ascertain that they are not sources of vanadium contamination. The standard sample is prepared by evaporating a known weight (about 1 pg.) of vanadium from solution onto a piece of polyethylene sheet which has been washed thoroughly with concentrated nitric acid and distilled water. The evaporation is effected by heating under an infrared lamp so that the polyethylene is not damaged. The standard solution is prepared by dissolving “Specpure” vanadium pentoxide in distilled water. The samples and standard are packed in individual small poly-
ethylene envelopes which are heatsealed and irradiated together in l/2inch diameter polyethylene containers for 4 minutes a t a thermal neutron flux of 10l2neutrons/sq. cm./sec. Reagents. Where possible high purity reagents are used. Cupferron solutions (5% w./v.) are unstable, so only small amounts are prepared a t a time, and these can be kept in dark bottles in a refrigerator. Destruction of the Organic Matrix. The standard may be digested in the normal manner or, if preferred, it may be shaken with the vanadium carrier/ sulfuric acid mixture in the cold, when complete exchange is obtained. The technique chosen for digestion of the sample is as follows. A 1.5-mg. sample of vanadium carrier (0.5 ml. of a 0.05M ammonium vanadate solution) and one drop of molybdenum carrier (10 mg./ml.) are added t o 3 ml. of 1811.1 sulfuric acid, and the mixture is heated in a 125-ml. tall form silica beaker until the acid is refluxing on its walls about 1 inch above the surface. The piece of tooth or tissue, which weighs up to 0.5 gram, is dropped into the acid and digests in 60 to 90 seconds with heavy charring. The charring is removed by the addition of 20 or 30 mg. of sodium nitrate. The solution, which is green to yellow and sometimes contains a white precipitate of calcium sulfate, is cooled as follows: swirl the solution in the flask in air for 30 seconds; cool further by immersing the flask in boiling water for a few seconds; bring to normal temperature by immersion in an ice bath. VOL 37, NO. 10, SEPTEMBER 1965
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