2-alkylpyrroles have a shorter retention time than the 3-isomers as was to be expected if the alkyl group in the 2position hinders attraction of the iminohydrogen for the column substrate. Likewise, the retention time of N-methylpyrrole is much shorter than the Cmethylpyrroles and even pyrrole itself. If the logarithm of the retention times is plotted against the carbon number of the alkyl group, the points fall on two straight lines. The single point for the C-methylpyrroles is on the extrapolated line for the 3-alkylpyrroles indicating that the small methyl group in the 2-
position is unable to interfere with the attraction between the pyrrole and the substrate. However, a methyl group on either side of the imino-hydrogen does interfere with the attraction, since the retention time of 2,5-dimethylpyrrole is slightly shorter and the retention time of the 2,4-dimethylpyrrole is slightly longer than that of 2-ethylpyrrole (which has the same molecular weight).
(2) Hinman, R. L., Theodoropulos, S., Ibid., 28, 3052 (1963). ( 3 ) Martinet, J., Bull. SOC.Chim. France 1948, 71. (4) Skell, P. S., Bean, G. P., J . Am. Chem. SOC.84, 4655 (1962).
GERRITTP. BEAN Chemistry Department Douglass College Rutgers-The State University New Brunswick, N. J.
LITERATURE CITED
(1) Griffin, C. E., Obrycki, R., J . Org. Chem. 29, 3090 (1964).
RECEIVED for review February 24, 1965. Accepted March 22, 1965.
Anion Exchange Separation of Beryllium SIR: I n comparison to the relatively great number of methods hitherto published concerning cation exchange separations of beryllium, only a few techniques have been developed based on anion exchange. Beryllium does not readily form anionic complexes which can be retained on basic resins. With some exceptions, the anion exchange separation methods developed so far are based on the nonadsorbability of beryllium and the retention of anionic complexes of other elements. Investigations by Kraus, Nelson, and Smith (9) carried out in aqueous hydrochloric acid media showed that the adsorption of beryllium is negligible a t all acid concentrations. Buchanan (2) developed a method based on these observations for the separation of beryllium from uranium and fission products using 9 N hydrochloric acid. Florence (3) similarly separated beryllium from some other elements interfering in the final determination using the morin method. When concentrated lithium chloride solutions are used, according to Kraus et al. (8), beryllium is weakly adsorbed on Dowex 1 and can be separated from the alkali metals and magnesium which pass into the effluent unadsorbed. I n contrast, beryllium from dilute aqueous hydrofluoric acid-hydrochloric acid mixtures is significantly adsorbed on Dowex 1. This fact was utilized by Nelson, Rush, and Kraus (12) to separate beryllium from aluminum which passed into the eluate first. Investigations by Faris ( 2 ) .showed that beryllium also is strongly retained on Dowex 1 from pure aqueous hydrofluoric acid solutions. However, scandium, titanium, zirconium, uranium, aluminum, and other elements are strongly coadsorbed with the beryllium.
Sutton (14) showed that both the fluoride complexes of beryllium and aluminum can also be adsorbed on Dowex 1 in the hydroxide form and separated from calcium, magnesium, iron, and phosphate which are not retained by the resin. A dilute sulfuric acid medium (pH 1.5) has been used by Silverman and Schideler (IS) to separate gram quantities of metal ions-uranium in particular-from microgram quantities of beryllium. Later Korkisch and Ahluwalia (5) showed that for the same purpose a medium consisting of 95% methanol-5yc 5N nitric acid can be used from which solution uranyl nitrate is preferentially adsorbed, whereas beryllium passes into the effluent accompanied by other elements such as vanadium, magnesium, calcium, aluminum, gallium, and indium. The adsorption of beryllium on Dowex 1 has also been investigated by Misumi and Taketatsu (IO)and Nelson and Kraus ( 2 2 ) in carbonate and citrate solutions, respectively. I n such media, however, separation of beryllium from other elements such as other group I1 elements-uranium, etc.-is relatively poor. None of the above anion exchange methods separates beryllium from practically all other elements. The present investigations were undertaken using organic solvent-mineral acid solutions because previous investigations carried out by Fritz and Waki ( 4 ) in isopropanol-nitric acid media, as well as by Korkisch and Hazan ('7) in organic solvent-hydrochloric acid media, have shown that magnesium and calcium are adsorbed on a strongly basic resin and can be separated chromatographically. Because of the small ionic radius of beryllium it was therefore expected
that this element would be less strongly adsorbed than magnesium and the alkaline earth metals and also aluminum. The present investigations show that this is actually the case so that separation from these elements and virtually all other cations having ionic radii greater than that of beryllium is possible. EXPERIMENTAL
Reagents. T h e resin used for t h e separations and measurements of t h e distribution coefficients by the column method (6) was Dowex 1, X8 (100- to aOO-mesh, chloride or nitrate form). Before transferring it to the ion exchange columns the resin in the suitable form was soaked in either 90% isopropanol-10% 6N hydrochloric acid, 90% isopropanol-10% 5N nitric acid, or any other. organic solvent mixture containing one or the other of these two acids. Standard solutions of beryllium, aluminum, magnesium, iron(III), and many other elements were prepared by dissolving the chlorides and nitrates of these metal ions in 6147 hydrochloric acid and 51' nitric acid, respectively. The pure organic solvents used were methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, acetone, tetrahydrofuran, dioxan, 2methoxy ethanol-1 (methyl glycol), and 2-ethoxy ethanol-1 (ethyl glycol). The eluting solution was 90 volume % isopropanol-10 volume % 6N hydrochloric acid. Apparatus. For the separations, resin columns 30 cm. long with a diameter of 1.0 cm. were used. Onegram columns were employed for the determination of the distribution coefficients with the column method (6). Recommended Procedure. To separate beryllium from aluminum, iron, magnesium, calcium, uranium, and other elements, the resin bed is VOL. 37, NO. 6, M A Y 1965
757
first pretreated by passing through 100 ml. of the eluting solution. Then the sorption solution, prepared by mixing 2 ml. of 6N hydrochloric acid with 18 ml. of isopropanol and containing beryllium as well as the metal ions to be separated from it, is passed through the column using a flow rate of about 0.2 nil. per minute, the normal backpressure of such a resin column under this condition. Afterward the resin bed is washed with the eluting solution and each 5-ml. fraction of the effluent is analyzed for beryllium, which in all cases leaves the column ahead of all other metal ions investigated except the common alkali metals, ammonium ion, and phosphoric acid. Beryllium is eluted after 150 ml. of the eluting solution have passed through the column; the breakthrough volume of aluminum is reached after a further 20 ml. When milligram quantities of beryllium are present, the beryllium can be determined directly by titration with 1JI sulfosalicylic acid after the addition of a few drops of a 1% solution of Neothoron in methanol and solid sodium acetate until no further color change in the solution can be observed (an excess of the acetate does not interfere). I n the end point the color changes from violet to pink. If microgram amounts of beryllium are expected to be present, the solution is evaporated to dryness on a water
bath (organic matter or ammonium salts must not be removed by ignition because beryllium will be lost by such a treatment; wet ashing is the only acceptable means). The residue, containing not more than 20 pg. of beryllium, is taken up in 1 ml. of 6,V hydrochloric acid; then 1 ml. of the Neothoron solution and 1 ml. of 0.1M EDTA solution (disodium salt) are added, and the solution is diluted to 10 ml. with 2M sodium acetate. Spectrophotometric measurement is then carried out at 570 mp against a reagent blank. I n the presence of 10 pg. of beryllium per 10 ml. of measuring solution, the absorbance is 0.40 if measurement is carried out using a Beckman Model B spectrophotometer and a 1-cm. cell. The addition of E D T A i reduces the number of interfering elements considerably so that in practice the small amounts of aluminum, iron (III), and other common elements which may be introduced during the processing of the eluate before measurement do not cause any interference. The nieasurement is also not disturbed by great amounts of alkali metals or ammonium salts, or by phosphoric acid if the concentration of the latter does not exceed 10 mg. (as ammonium dihydrogen phosphate) per 10 ml. of measuring solution. Interference in the final determination of beryllium after carrying out the
Table I. Distribution Coefficients of Beryllium, Aluminum, and Magnesium, in 90% Organic Solvent-1 0% 6N Hydrochloric- and 5N Nitric Acid Solutions (500-pg. load) 6N Hydrochloric Acid 5N Nitric Acid Solvent Be A1 Mg Be A1 31g 1 l(O.0) 1 (0.0) 1 l(O.0) l(O.0) Water Methanol 3 (2) 2 2 (0.0) 3 (1.5) 15 2 (1.33) 6 5 (3.25) 2 2 5 (1.25) 4 (2) 2 4 (2) Ethanol n-Propanol 5 22 (4.4) 22 (4.4) 2 6(3) 11 (3) 10 (3.33) 6 24 (4) Isopropanol 22 (3.66) 3 6 (2) 20 (5.0) 4 6 (1.5) %-Butanol 6 35 (5.83) 33 ( 5 . 5 ) Isobutanol 5 10 (2) 18 (3.6) 9 80 (8.88) 36 (4) 4 11 (2.75) 8 (2.0) 10 40 (4) 33 (3.3) Acetone 2 (0.0) 3 5 (1.16) 2 2 (0.0) Methyl glycol 3 3 (0.0) 2 2 (0.0) 2 (0.0) 7 (2) Ethyl glycol 3 5 6 (1.71) 15 (2) 22 (2.9) Tetrahydrofuran 7 5 4 10 (2.5) s (2)
Dioxan
5
a
lO(2)
12 (2 4)
Two liquid phases.
Table
II.
Separation of Beryllium from Other Elements in Isopropanol-1 0% 6N Hydrochloric Acid Medium
5
Beryllium Found mg. Pg. (5) 5.01 (5.1)
5
(5)
5.00
5
(5)
4 98
5
(5)
5 01
5
(5)
4 99
Taken mg. Pg.
758
90%
Foreign ion simultaneously used, mg. Mg(II)(lO), Ca(II)(lO), Sr(II)(l), Ba(II)(0.2), Cu(II)(lO), Zn(I1) ( l o ) , Cd(II)(lO), and Hg(I1)
(5). (4.9) Al(III)(lO), Ga(III)(lO), In(III)(lO), Sc(II1) (lo), Y(III)(lO), Ln(III)(10), Sn(II)(lO), Pb(1I) ( l ) ,Ti(IV)(5),Zr(IV)(5),and Th(IV)(lO). (5 2 ) Bi(III)(lO), J-(T-IT)(lO), Cr(III)(lO), Mo(V1) ( l o ) , and UO2(II)(10). (4 9) Mn(II)(lO), Fe(III)(jO), Co(II)(20), and Ni(I1) (10). ( 5 0) All above mentioned elements in 5 mg. amounts.
ANALYTICAL CHEMISTRY
column operation may be caused only by the presence of greater amounts of phosphate which cause a decrease in the absorption values. Uranium would interfere seriously if not separated before measurement of the beryllium. RESULTS
In Table I the adsorption characteristics of beryllium, aluminum, and magnesium in various organic solventmineral acid mivtures as determined by the column method (6) are shown. For the purpose of comparison, water has been included in Table I. I n the parentheses following the Kd values of aluminum and magnesium, the separation factors calculated according to the equation Kd, Al, or Mg divided by the Kd of Be are also listed. From these results it is seen, that the media containing the higher aliphatic alcohols n-propanol, isopropanol, n-butanol, and isobutanol are most suitable for the analytical separation of beryllium from these two elements in both hydrochloric and nitric acid mixtures. When the separation factors in these higher alcohol solutions are compared, it can be seen that their hydrochloric acid mixtures are to be preferred over the solutions containing nitric acid because of the higher separation factors in the former media. Among these, isopropanol was more suitable than the other alcohols because in the 90% mixture of this alcohol with 10% of 6 N hydrochloric acid, a more rapid flow rate through the columns is attainable. However, the separation factors of aluminum and magnesium are somewhat lower than in the other higher alcohols. High flow rates can also be obtained when passing the acetone-hydrochloric acid mixture, but under this condition iron(III), gold(III), molybdenum(VI), and other elements will accompany beryllium into the effluent. When 90% isopropanol-10% 6iV hydrochloric acid is used, however, these elements as well as virtually all others except the alkali metals, ammonium ion, and phosphoric acid are strongly retained by the resin so that they can, even if present in great excess, easily be separated completely from microgram and milligram amounts of beryllium. This is not surprising, for it was observed by Korkisch and Ilazan ( 7 ) that virtually all metal ions are more or less strongly adsorbed from 90% isopropanol-lO% 61V hydrochloric acid medium including elements such as the rare earths, titanium, zirconium, thorium, vanadium, chromium(III), molybdenum(VI), etc., which are only slightly or not a t all adsorbed on the resin from pure aqueous hydrochloric acid solutions. With the procedure described above, several separation experiments were
carried out. A few typical results which can be achieved without cross-contamination of the beryllium fractions by the various elements tested are recorded in Table 11. These results show that in all cases quantitative separation of the beryllium from the elements can be achieved in one operation. Consequently it can be expected that this method will be applicable for the assay of microgram and milligram quantities Of beryllium in a variety of materials such as ores, rocks, alloys, fission products, etc., provided the phosphate content of these is not too high to interfere with the beryllium determination.
LITERATURE CITED
( & ~ (2) Faris,
J.
~ ( .~ p., A
~ hJ.5 Inorg. ~~ : ~Nuel. ~ ~
~
cHEM. ~
32, ~ ,520 .
(1960).
(3) Florence, T. M., Anal. Chim. Acta 20, 472 (1959). (4) Fritz, J. S., Waki, H., ANAL.CHEM. 35, 1079 (1963). (5) Korkisch, J., Ahluwalia, S. P., Talanta 11, 1623 (1964). (6) Korkisch, J., Hazan, I., ANAL.CHEM., in press. ( 7 ) Korkisch, J., Hazan, I., Talanta 11, 1157 (1964). (8) Kraus, K. A., Nelson, F., Clough, F. B., Carlston, R. c . , J . Am. Chem. soc. 77, 1391 (1955). ( 9 ) Kraus, K. A., Nelson, F., Smith, G. W., J . Phys. Chem. 58, 11 (1954).
(10) Misumi, S., Taketatsu, T., Bull. Chem. Bot. Japan 32, 877 (1959). (11) Nelson, F., Kraus, K . A,, J . Am. ~ Chem. ~ SOC.77, 801 (1955). (12) Nelson, F., Rush, K. X, Kraus, K. A., Zbid., 82, 339 (1960). (13) Silverman, L.,152Schideler, ANAL. CHEM.31, (1959). 11. E., (14) Sutton, D. c . , C'SAEC Rept. HASL134, 1963.
JOHANN KORKISCH FRANZ FEIE
Analytical Institute University of 1-ienna, I X Wahringerstrasse 38 Vienna, Austria. Acknowledgment is made to the donors of The Petroleum Research Fund, administered by the American Chemical Society, for support of this research (PRF-grant No. 1587-A3).
Elimination of Container Effects in Activation Analysis of Oxygen SIR: A major difficulty in determining trace amounts of oxygen in metals is the problem of correcting for background. I n the usual fast-neutron activation analysis procedure, the background is a composite of three factorssample container, atmosphere in the container, and normal gamma ray radiation to which the scintillation detector is exposed. The predominant factor, by far, is the sample container. Stallwood, Mott, and Fanale (3) have shown that typical plastic sample containers have a n oxygen content of about 300 to 1500 p.p.m. Unfortunately, an accurate correction for this source of oxygen activity cannot be accomplished by merely activating and counting the empty container. Various techniques have been proposed to solve the problem of high background due to the container. Coleman (2) essentially eliminated the oxygen activity of the container by using a 6-inch polystyrene capsule, wherein the sample was activated in one end and counted in the other. One problem with this device is that the pneumatic shuttle system must be straight or designed so as to have large angle bends to accommodate the sample container. I n the technique adopted by the container is fabricated Steele (4, from copper tubing having a n oxygen content of about 5 p.p.m., and the background is further reduced by encapsulating the sample in a n inert atmosphere. The reported detection limit, when using a flux of about 10'" neutrons/second, is about 1 p.p.m. I n the simple procedure being used in this laboratory, the metal sample is activated in a plastic countainer, but is removed therefrom and dropped into the scintillation detector. The total delay time prior to counting is increased from 3.0 to 4.5 seconds by the manual
t OrOonic
-& Mlasurtd gommo + beto attrnuo t ion -Q- Theoretical gomma ottcnuolion
W"
I
AREAL
i
3
OENSITY, glcm'
Figure 1 . Comparison of observed and theoretical attenuation
operation. However, the delay is more than offset by the elimination of all background except that due to normal room background. PROCEDURE
The metal sample is cut to size and filed clean prior to surface etching with acid. The encapsulated sample is placed in a port in the shuttle tube, the timingsequencing controller is energized, and the sample is irradiated for 15 seconds. The container, upon return to the counting room, is ejected and caught by hand. The cap is quickly removed, and the sample is dumped into a test tube in the well crystal. The counting delay time is set a t 4.5 seconds to allow this operation to be carried out successfully. The sample is counted for 30 seconds, the equivalent of 4 half lives of the P o . RESULTS
Several different shaped samplescylindrical, parallelepiped , ellipsoidal, and hemiellipsoidal -were cut from a National Bureau of Standards steel sample No. 1046 (0.106% oxygen) to determine what, if any, effect could be attributed to the shape. Weights varied from 4.454 to 14.770 grams, but
all the specimens were of the same length. The relative standard deviations for the oxygen determinations ranged from j ~ 2 . 4 7 for ~ the right cylinder to i 5 . 5 % for the hemiellipsoidal-shaped sample. Calculations, similar to those presented by Anders (I), were made to determine the effects of neutron shadowing and gamma ray attenuation. How-
Table
l.
Comparative Analyses of Oxygen in Metals
Oxygen, p.p.m. Sample Fusion Activation NBS steel 1040 1805 203 f 18 NBS steel 1043 200 23 f 4 Beryllium 200b 56 f 8 Molybdenum-1 360b 440 f 30 Molybdenum-2 lob 16 f 3 S'anadium 410b 340 f 30 Cerium-1 160b 130 f 15 Cerium-2 70b 70 f 10 Lanthanum 420b 370 i 35 Chromium 90b 120 f 15 Tin l o b 9 f 5 Tungsten 3 f 2 a NBS Certificate of Analysis (vacuum fusion). b Inert gas fusion analysis. h'ot determined.
VOL. 37, NO. 6, MAY 1965
a
759
