effects of 25 aluminum impurities were considered insignificant. Batches of 25 aluminum were spectrographically analyzed and found to contain less than the detection limit of 10 p.p.m. of boron. Boron in blanks is therefore less than 1% of the boron measured in samples. FUSIONCONDITIONS.Sodium carbonate fusion has been recommended (1, 6) for dissolving boron carbide. A factorial experiment was made t o establish effects of fusion variables. Levels of sodium carbonate were 2, 3, and 4 grams; fusion times were 15, 20, 25, and 30 minutes; amounts of boron carbide were 3.5 and 11 mg. Temperature of fusion was constant a t 900°C. in a muffle furnace. Covered platinum crucibles were used. Statistical interpretation of the data indicated no significant variables; any combination of amount of sodium carbonate and fusion time gave quantitative boron recovery a t both boron carbide levels. The minimum time was chosen for the proposed procedure. The maximum level of sodium carbonate was
selected to ensure adequate mixing by different analysts.
puted standard deviation n-as 1.8%. This agrees well with the predicted value of 1.4% from the calibration data.
PRECISION
An actual calibration equation based on nine standards for the proposed procedure is A = 15.62 B
+ 0.0103
in which A = absorbance B = mg. of boron in final 25 ml. The standard deviation of the intercept was 0.0057. A t test indicates the intercept not to be significantly different than zero. The standard deviation of the absorbance was 0.0079. This corresponds to 1.4y0standard deviation a t about the mid-point, 0.03 mg. of boron, of the calibration curve. Another estimate of the precision was calculated from a series of control samples submitted a t the rate of one per week over a 2-month period. These samples were analyzed by personnel trained under the laboratory’s Training and Testing Program (8). The com-
LITERATURE CITED
(1) American Society for Testing Ma-
terials, Philadelphia, “ASTJI Methods of Metals,” 1950. (2) Churchill, H. V., “Chemical Analysis of Aluminum,” 3rd ed., p. 30, Aluminum Research Laboratories, X e r Kensington, Pa., 1950. (3) ‘Cogbill, E. C., Yoe, J. H., Anal. Chim. Acta 12, 455 (1955). (4) Dempsey, R. H., Jacobson, J. J., Levy, S., Wolfe, B., .Yudeonics 15, KO.3, 44 (1957). (5) Ellis, G. H., Zook, E. G., Baudisch, O., ANAL.CHEM.21, 1345 (1949). (6) Furman, iY. H., “Scott’s Standard Methods of Chemical iinalysis,” 5th ed., p. 181, Van Xostrand, Yew York, for Chemical Analysis
1939. ~. -
( 7 ) Hatcher, J . T., Kilcox, L. V., A i i . 4 ~ . CHEM.22, 567 (1950). (8) Huff, G. B . , Tingey, F. H., Ibid., 29, 19A-22A (August 1957). RECEIVED for reviev December 16, 1957. Accepted June 9, 1958. Kork was done under Contract So. AT(10-1)-205 for the U. S. Atomic Energy Commission.
Volumetric Determination of Thorium in Uranium Alloys HOBART
H. WILLARD,’
ARTHUR W. MOSEN,2 and ROSS D. GARDNER
The University of California, 10s Alamos Scientific Laboratory, Los Alamos, N.
b Thorium is determined in uraniumthorium, uranium-tungsten-thorium, and uranium-titanium-thorium alloys by precipitation as the fluoride, using lanthanum as a carrier, followed by titration with EDTA. Eriochrome Cyanine RC is used as the indicator in the titration. In 161 determinations of known solutions simulating the above alloys with a thorium content of 0.1 to 3.0%, an average of 99.4% of the thorium was found. The relative standard deviation for individual values was 0.5670 with no significant difference in the various synthetic solutions.
T
investigation was initiated because of a need for a n analytical iiiethod t o determine 0.1 to 3y0thorium in uranium alloys which might also contain tungsten or titanium. Nost of the older accepted methods for the determination of thorium are gravimetric (4, 6). A large number of insoluble compounds have been used in separations, but the element is usually HIS
1 Present address, University of Michigan, Ann Arbor, Mich. * Present address, General Atomic Corp., San Diego, Calif.
1614
ANALYTICAL CHEMISTRY
M.
weighed as the oxide after ignition. The oxalate method, which has been used in this laboratory for the determination of thorium in uranium alloys, has not been satisfactory for alloys containing less than 0.5% thorium because the loss due to solubility becomes significant (6). Increasing the size of the sample is impractical because of the limited solubility of uranyl oxalate. A spectrophotometric procedure ( 7 ) is available for very small amounts of thorium in uranium, but it lacks the precision required for the range under consideration. Furby ( 2 ) gives a procedure for determining larger amounts of thorium in uranium using a titration with EDTA [disodium (ethylenedinitrilo) tetracetic acid] after a separation as the benzoate. However, the benzoate precipitation involves a troublesome adjustment of p H and is an incomplete separation of thorium from a number of other metals. The precipitation of thorium fluoride in the presence of other metals has been described by Grinialdi and Fairchild (3). They showed that it was a good separation from uranium and certain other metals such as tantalum, niobium, titanium, zirconium, and iron. B y using
a carrier they obtained quantitative recoveries of less than milligram amounts. Fritz and Ford ( I ) investigated the titration of thorium Kith EDTA using Alizarin Red S as the indicator. A combination of these two processes, as described in this paper, has afforded a rapid and accurate procedure for the determination of thorium in uranium alloys. The thorium fluoride with a carrier of lanthanum fluoride is ignited to the oxide, dissolved in nitric acid, and evaporated with perchloric acid. The solution is adjusted to a p H of 2 and titrated with EDTA using Eriochrome Cyanine as indicator. APPARATUS A N D REAGENTS
Polyethylene beakers, funnels, and stirring rods were used where hydrofluoric acid solutions were involved. Other items were standard laboratory equipment. All chemicals used were analytical reagent grade. Ammonium Fluoride Solution. A 10% solution was kept in a polyethylene bottle. EDTA, Standard Solution. A 0.025M solution was prepared by dissolving 9.3088 grams of dry, reagent quality, disodium (dinitrilo) tetraacetate in water and diluting to 1
liter. (The dry reagent may be considered a primary standard or the solution may be standardized against pure thorium oxide.) Indicator Solution. One hundred milligrams of Eriochrome Cyanine RC (Hach Chemical Co., Ames, Iowa) was dissolved in 100 ml. of water. Lanthanum Nitrate Solution. Lanthanum nitrate was dissolved in water to make a solution containing 2 mg. of lanthanum per ml. Thorium Nitrate Solution. A solution containing 2 mg. of thorium per ml. was prepared by dissolving 4.7580 grams of pure thorium nitrate tetrahydrate in water and diluting t o 1 liter. It was standardized by titrating against the standard E D T A solution and also by determining the thorium gravimetrically by the oxalate method. Uranium Solution. Pure metallic uranium \?-as dissolved in hydrochloric acid and hydrogen peroxide and diluted to a concentration of 0.3 gram per ml. Wash Solution. Twenty-five milliliters of 48% hydrofluoric acid was added t o 475 nil. of water in a polyethylene n-ash bottle. RECOMMENDED PROCEDURE
Uranium-Thorium and UraniumTitanium-Thorium Alloys. Dissolve a sample, containing about 10 mg. of thorium, in concentrated hydrochloric acid, heating and adding hydrogen peroxide from time t o time as necessary to complete the dissolution. If the sample is already in solution in hydrochloric nitric, or sulfuric acid, use a suitable aliquot. Dilute the sample solution to 25 ml. and add 5 ml. of the lanthanum solution. Adjust the pH to between 2.0 and 3.0 with ammonium hydroxide using a glass electrode and stirring constantly n i t h a magnetic qtirrer. (The solution a t this point should contain no precipitate.) Transfcr the solution to a 250-ml. polyethylene beaker and add a little ashless filter paper pulp. Add from a polyethylene graduate 5 ml. of 48% hydrofluoric acid and 20 nil. of 10% ammonium fluoride solution, stirring with a polyethylene rod. Be careful to avoid contact between hydrofluoric acid solutions and the skin. If such contact occurs, wash immediately with dilute ammonium hydroxide. Allow the precipitate to digest for at least 2 hours (preferably overnight) a t room temperature. Filter the solution through a 9-cm. Khatman $42 or similar dense, ashless paper. Use a plastic funnel, n ith no vacuum, and place a little paper pulp in the filter before starting the filtration. Kash the precipitate with hydrofluoric acid wash solution until all the uranium i. removed, and use a piece of dry filter paper to wipe o u t the beaker t o ensure complete removal of the precipitate. Ignite the precipitate in a platinum crucible a t 800" C. Wash it into the beaker in which the sample Mas dissolved. Heat some nitric acid in the crucible to dissolve any thorium
oxide that may have adhered to it and rinse it into the beaker. Add 15 to 20 ml. of nitric acid and heat until the oxide has dissolved. If this requires more than 20 to 30 minutes, add 1 drop of 5% hydrofluoric acid and continue heating. To the clear solution. add 1 ml. of perchloric acid, and evaporate until a moist residue remains. Dissolve this in 20 to 25 ml. of water, and adjust the pH to between 2.0 and 2.5 with hydrochloric acid or sodium hydroxide using a pH meter and magnetic stirrer. Add 2 drops of indicator solution and titrate with standard EDTA solution until the color' changes sharply from purplish red to salmon pink. Uranium-Tungsten-Thorium Alloys. Dissolve the sample as described in t h e preceding section, using a definite volume of concentrated hydrochloric acid and about 5 ml. of hydrogen peroxide. Transfer the solution immediately t o a polyethylene beaker and add 5 ml. of 48% hydrofluoric acid and 20 ml. of 10% ammonium fluoride. Before the addition of fluoride the solution should have a p H of 2 to 3; but, because the fluoride must be added before the tungstic acid precipitates and because the glass electrode should not be used in the presence of fluoride, the proper conditions are approximated by neutralizing, with a measured amount of ammonium hydroxide, the excess acid used to dissolve the sample. (This volume can be determined by carrying a sample, without filtering, through the first procedure and measuring the amount of ammonium hydroxide needed to bring the pH to 2 to 3, using a glass electrode.) Add 5 ml. of the lanthanum nitrate solution and some filter paper pulp, filter the solution, and continue the procedure as described above. DISCUSSION
Alloy samples dissolved most readily in hydrochloric acid, thereby permitting the thorium fluoride t o be precipitated from hydrochloric acid solution. However, determinations were made in which the thorium fluoride was precipitated from solutions containing nitric or sulfuric acid. This had no apparent effect on thrx results.
Table I. KO.
of
Determinations 9 S 9 10 24
1
5 10
13 27 15 9 15
Thorium Taken, 3lg. 30 6 0 9 0 12.0 10 0 30 0 40 0 50 0 19 78 9 89 10 00 9.82 5 89
I n the analyses of actual samples. occasionally an undetermined impurity masked the end point in the titration. I n these cases it was necessary to reprecipitate the thorium from the solution of the ignited oxide. Evaporation of the solution of the oxide with perchloric acid served to remove traces of fluoride which interfered seriously with the titration, but as the oxide was not dissolved by perchloric acid, it was necessary to dissolve it first in nitric acid. Large amounts of perchloric acid made the end point indistinct. The color change of the indicator was sharpest a t p H 2. Other indicators tried were alizarin, carminic acid, chromazurol, ammonium purpurate, and purpurin sulfonate. Xone of these could be used in the presence of lanthanum. Attempts were made to destroy the filter paper with nitric and perchloric acids instead of igniting the fluoride to oxide. Although this u'as rapid and convenient, the resulting solution showed no end point when titrated Lyith EDTA. This mas apparently not due to any material removed from borosilicate glass, because small amounts of boron and arsenic showed no effect. K h e n quartz beakers were used, no trouble was experienced at first, but in later rxperiments a turbidity was produced \\ hen the pH was adjusted to betneen 2 and 2.3, and no titration wa> possible. S o explanation has been found for these phenomena. The volume of solution from which thorium fluoride n as precipitated varied from 50 to 100 ml.. but with 3 grams of uranium in 50 ml. of solution a greenish yellow, crystalline precipitate of uranyl ammonium fluoride was formed. Under these conditions a volume of at least 100 nil. is recommended. Effects of Titanium and Tungsten. When titanium was present, hydrogen peroxide prevented its precipitation. It was usually not present in the thorium fluoride but even large amounts of it did not interfere nith the E D T A titration because the ti-
Determination of Thorium in Known Solutions
Titanium Tungsten Present, Present, hIg. Mg.
10 10 10 20 10
Uranium Present, Grams 3.0 3.0 3.0 3.0 2 0 3 0 2 7 1.7 2 2 2 2 2
Average Thorium Found,
7% 100.4 99.6 99.7 99.6 99.4 99.6 100.0 99 2 99.1 99 3 99.6 99.5 99.0
VOL 30, NO. 10, OCTOBER 1958
Standard Deviation,
%
1.03 0 40 0.30 0.27 0.36 0.32 0.22 0 33 0.46 0.34 0.62
0.45 0.58
1615
tanium complex with t h e reagent is unstable. When titanium was present, t h e thorium fluoride had a bluish tint and turned brown on ignition, because of t h e presence of a trace of uranium which is not carried down in t h e absence of titanium. Tungsten tended to precipitate as tungstic acid shortly after the sample was dissolved. An excess of hydrogen peroxide kept a limited amount of tungsten in solution but was inadequate for 20 mg. or more. If the precipitate of tungstic acid was allowed to digest for a time, it did not always redissolve when hydrofluoric acid was added, but remained with the thorium fluoride, 11 here it interfered with the titration. A set of six determinations was made in 11 hich the tungstic acid was allon ed to digest, then removed by filtration prior to the precipitation of the thorium fluoride. I n this case, however, the recovery of the thorium was only about 75%. dpparently the other 25’% was carried down by the tungstic acid. When such amounts of tungsten \\ere present, best results were obtained by adding the hydrofluoric acid as soon as the alloy was in solution and neutralizing part of the acid later by adding a calculated amount of ammonia. This
prevented any tungsten from contaminating the thorium precipitate. EXPERIMENTAL RESULTS
Determinations were carried out on solutions made u p to sirnulate the alloys under consideration in which the thorium content would vary from 0.1 to 3.0y0 (Table I). I n a total of 161 determinations, the average thorium found \vas 99.4% of the amount taken. The relative standard deviation for individual values n a s 0.56y0,with no significant difference in the different synthetic solutions. The simulated titanium alloy was made from solutions containing uranium, thorium, and titanium. Honever, in the case of tungsten, because the main problem was t o keep it in solution while the thorium fluoride \vas precipitated, an alloy of tungsten and uranium \vas prepared and saniples from it nere dissolved in the prez-ence of known amounts of thorium. The determination m s then made according to the second procedure given. The amount of thorium that can be determined by this method is limited only by the precision of the titration. Three milligram$ !vas the smallest
amount titrated in these esperitnents, but by using a more dilute EDTA solution and, if necessary, a photometric end point, much smaller amounts could doubtless be determined. -45 little as 0.03 mg. of thorium was recovered from complex synthetic mixtures by Grimaldi and Fairchild !3). LITERATURE CITED
( 1 ) Fritz, J. S., Ford, J. J., .%SAL. CHEJI. 25, 1640 (1953). (2) Furby, E., Btoniic Energy Research Est,ab. (Gt. Brit.) C/R 1435, hIay 1954. ( 3 ) Grimaldi, F. S., Fairchild, J. G., U. S. Geol. Survey Bull. 1006, 133 (1954). ( 4 ) Hillebrand, W .F., Lundell, G. E. F., Bright, H. .%.,Hoffman, J. I., “Applied Inorganic Analysis,” pp. 533-42, Riley, Xew k-ork, 1953. (5) Iiall, H. L., Gordon, L., ANAL. CHEM.2 5 , 1256 (19531. (ti) Scott, W.S. “Standard Methods of, Chemical Analysis,” 5th ed., Vol. 1, pp. 196-553, Van Sostrand, Xew York, 1939. ( i )Thomason, P. F., Perry, 11. A., Byerlj-, IT. M., -4s.4~. CHEXI. 2 1 , 1293 (1949).
RECEIVED for review January 14, 1958. dccepted May 31, 1958. Work done under the auspices of the U. S. Atomic Energy Commission.
Paper Chromatography of Streptothricin Antibiotics Differentiation and Fractionation Studies MARTIN 1. HOROWITZ’ and CARL P. SCHAFFNER Institute o f Microbiology, Rutgers, The State University, New Brunswick, N. J. ,An adaptation of circular paper chromatography has been used for the survey of a large number of poorly defined, peptide-like antibiotics related to streptothricin. Circular paper chromatography was found to be superior to linear, ascending, or descending chromatographic techniques. Most of the antibiotic preparations examined revealed multiple components after chromatographic separation. The solvent system, 1 -propanol-pyridine-acetic acid-water ( 1 5 :10 :3 :12), used in these studies was alsoeffectively applied to large-scale, cellulose powder column partition chromatographic separation of these antibiotics. Application of the preparative aspects of this chromatographic technique to the qualitative and quantitative analysis of several streptothricin complexes is now under investigation.
1616
ANALYTICAL CHEMISTRY
I
search for new antibiotics, substances are frequently found which apparently belong to the large group of ill-defined antibiotics called streptothricins. Reportedly tosic, thrse antibiotics have varied biological activities against both Gram-positive and Gram-negative bacteria, fungi, and viruses. The purpose of this study was to devise rapid paper chromatographic tnethods for the separation of the various members of the streptothricin family of antibiotics, enabling efficient characterization of unidentified, niicrobiologically related antibiotics obtained from a screening program. The streptothricins are uwally referred t o as basic, Ivater-soluble substances which are insoluble in most organic solvents other than the lower alcohols. The basicity can be attributed to the presence a3 structural units of the basic amino acids, streptolidine N THE
( d ) , [also referred to as gearnine ( 3 ) roseonine ( I I ) ] , and $.e-dianiino-ncaproic acid (6,19). The nenly described aniino sugar, 2-amino-2-deosya-D-gulose has been found in streptothricin and streptolin B (,’IS). Because most of the streptothricin antibiotics exist as complexes, it has al\vaj-s bwn desirable t o obtain clrar-cwt separations and differentiations of coniponents by some convenient paper chromatographic technicjue. This has bren tlifficult,, because with a large iiuinbrr of chromatographic solvent systems, the various streptothricins 1,shibit similar R, values, as well as a marked tendency towarti streaking and tailing. A varirty of analytical approaches Present address, Gastroenterology Re: aearrh Laboratory, The Mount Sinai Hospital, S e x l o r k , S . T.
