The results obtained in the analysis of XBS samples are set forth jn Table
Table IV.
117.
The results given in Table I1 demonstrate that this method can be applied satisfactorily t o the estimation of microgram quantities of cobalt in slurries of thorium oxide which contain large quantities of thorium and lesser amounts of nickel, chromium, iron, and other impurities. The coefficient of variation is less than 5%. Even for cobalt in concentrations of 0.3 to 1 y per gram in contaminated slurries of thorium oxide, the coefficient of variation is no greater than 10% (Table 111). It is unnecessary to use a standard addition technique. No significant difference in test results (Table 111) is to be observed between results obtained with and without the use of this technique. This method is also suitable for the determination of cobalt in steels and other alloys as is evidenced by the results for the analysis of NBS standard samples given in Table IV. Apparently, no prior separation by means of an anion exchange resin is necessary if the ratio of interferences to cobalt is below the tolerance limits, or if the foreign ions can be masked with citrate or do not form che-
Cobalt in NBS Standard Samples
Sample SBS KO 153
TS Pe Co-&Io-W steel
Certified Value 8 45
161
Si-Cr casting alloy
0 4i
126a
High-nickel steel
0 30
lates with PAN. Even though the Separation step was omitted in the analysis of NBS sample 153, the results are in excellent agreement with the certified value for cobalt. I n all probability, this method is also applicable to the determination of cobalt in a variety of sample types which were not tested, particularly t o materials which contain, as their primary constituents, metals which are not adsorbed on a Dowex-1 resin, such as aluminum, the alkali, and alkaline-earth metals. ACKNOWLEDGMENT
The authors acknowledge the assistapce of H. P. House and hl. A. Marler in the preparation of this manuscript.
rl V
Found 8 43 8 49 0 48 0 50 0 31 0 30
Difference Difference, yo -0 02
n
04 0 01 o n3 0 01
0 1 4
2
0 00 LITERATURE CITED
(1) Cheng, K. L., Bray, R. H., XSAL. CHEJI.27, 782 (1955).
(2) Harvey, A4.E., Manning, D. L., J . Am. Chem. SOC.72, 6688 (1950). (3) Kraus, K. A., Selson, F., International Conference on Peaceful Uses of Atomic Energy, Paper 837 (U.S.A.), August 1955. (4) Ringbom, A , , 2. anal. Chem. 115, 322 (1939). RECEIVEDfor review August 4, 1958. Accepted October 9, 1958. Division of Analytical Chemistry, 134th Meeting, ACS, Chicago, Ill., September 1958. Fork carried out under Contract No. W-7405-eng-26 at Oak Ridge National Laboratory, operated by Union Carbide Nuclear Go., division of Union Cftrbide Corp., for the Atomic Energy Commission.
Ultraviolet Spectrophotometric Determination of Thorium with 2,4-Dichlorophenoxyacetic Acid SACHINDRA KUMAR DATTA1 Chemisfry Deparfrnenf, Darjeeling Government College, Darjeeling, India
b The thorium salt of 2,4-dichlorophenoxyacetic acid is soluble in an aqueous ammonium carbonate solution, The solution of this saltlike compound shows maximum absorbance a t a wave length of 230 rnp and follows Beer's law. The spectrophotometric determination of thorium is based on the measurement of the absorbance of this solution. The sensitivity of the method is 0.0 19 y of thorium per sq. cm., but the accuracy is poor in samples containing less than 2 mg. of thorium. The common metals do not interfere, but strong interference is exhibited b y iron, cerium(lV), and zirconium. The optimum results are obtained in a concentration range between 2 and 1 4 mg. of thorium per liter.
T
was determined gravimetrically by Datta and Banerjee (3) using 2,4-dichlorophenoxyacetic acid (2,4-D). This reagent proved useful for the HoRImf
separation of thorium from the rare earths, zirconium, titanium, iron (4),and uranium ( 5 ) . It was also employed for the recovery of thorium from industrial wastes, like used gas mantles and tungsten filaments ( 2 ) . In these methods, thorium is precipitated with 2,4-D as the triphenoxate and the precipitate is ignited and weighed as thoria. The thorium derivative of this reagent is highly soluble in an aqueous solution of ammonium carbonate, a soluble saltlike compound probably being formed in the reaction. The solution of this thorium salt in ammonium carbonate exhibits absorption in the ultraviolet region of the spectrum. The spectral curve indicates maximum absorbance a t a wave length of 230 mp. The absorbance is probably caused by the phenyl group of 2,4-D in the thorium salt, as the ammonium salt of 2,4-D produces a very similar spectrum, although its maximum absorbance occurred a t 285 to 286 mp. Thorium in ammonium carbonate solution shows
an entirely different spectrum. The present paper examines the possibility of using spectrophotometric study in the determination of small amounts of thorium. REAGENTS AND APPARATUS
Reagents. 2,4-Dichlorophenoxyacetic acid was prepared and purified as before ( 3 ) . A 1% solution in water was prepared by heating the constituents. A stock solution of thorium nitrate was prepared from thorium nitrate tetrahydrate (analytical reagent, hlerck) and standardized with oxalic acid. Ammonium carbonate solutions of various strengths were prepared and estimated with standard sulfuric acid. The solutions of other metal salts, all analytical reagent quality, were pre1 Present address, Department of Chemistry, Victoria College, Cooch Behar, West Bengal, India.
VOL. 31, NO. 2, FEBRUARY 1959
195
pared and estimated by the standard methods. Apparatus. A Beckman spectrophotometer, Model DU, with 1-cm. quartz cells and ultraviolet attachments, was used to measure the absorbance. A Beckman p H meter, Model G, was used for p H measurements. EXPERIMENTAL
Absorption Spectra. A given amount of thorium nitrate solution was precipitated with a 1% solution of 2,4-D. The thorium salt was thoroughly washed with hot water and alcohol (75%) and then it was dissolved in 50 ml. of O.OlO6M ammonium carbonate solution. The absorbance of this solution was measured in 1-em. cells. a t the maximum sensitivity of the instrument; a t intervals of 5 mp, against a reference solution containing ammonium carbonate of the same strength, in the wave length range from 215 to 300 mp. Spectral curves for the ammonium salt of 2,4-D and for the thorium nitrate and the ammonium carbonate mixture, against an ammonium carbonate blank solution, were similarly obtained. The spectral curves given in Figure 1 show that the maximum absorbance for the thorium salt of 2,4-D occurred a t 230 mp, while that for the ammonium salt of 2,4-D is a t 285 to 286 mp. The thorium nitrate and ammonium carbonate mixture showed no peak for maximum absorbance within these wave lengths. Stability of Thorium Salt of 2,4-D in Ammonium Carbonate. It appears from the absorption spectra (Figure 1) that the thorium salt of 2,4-D is either stable in ammonium carbonate solution or it forms a saltlike compound with it. The thorium salt probably does not change to a thorium carbonate complex and 2,4-dichlorophenoxy ammonium acetate: as their spectral curves are different. The solution of the thorium salt of 2,4-D in ammonium carbonate, however, remained stable for about 3 days. After this time a marked decrease in the absorbance values was noted and the solution became slightly turbid because of hydrolysis. The formula of the complex may be determined by a method of continuous variations (1). Amount of Reagent. As the ammonium salt of 2,4-D does not show appreciable absorption a t 230 mp, a little free 2,4-D remaining adhered to the thorium precipitate, there was practically no change in its absorbance value a t that wave length. Concentration of Ammonium Carbonate. The amount of ammonium carbmate used to dissolve the thorium salt of 2,4-D is not critical. Similar results were obtained with 0.0033M 196
ANALYTICAL CHEMISTRY
Table I. Effect of Ammonium Carbonate on Absorbance of the Thorium
Salt of 2,4-D
Thorium in 2,4D Salt, Mg./Liter 10.54
Ammonium Carbonate, M
n. nnw,
Absorbance at 230 R.lp 0.543 0.548
0,0099
0,547
0.0033
0.0106 0.0132 0.0165
0.547 0.545 0.548
Table II. Molar Absorbance Index of Thorium-2,4-D-Ammonium Carbonate Complex
Molar
Thorium, Absorbance M X 108 Absorbance Index 0.111 12,211 9.09 0.221 12,156 18.18 22.70 0.277 12.203 27.20 0.327 12:022 36.30 0.440 12; 121 45.40 0.546 12,020 G3.60 0.772 12,138 Av. 12,124
to 0.0165M solutions of ammonium carbonate (Table I). Temperature. The solution of the thorium salt of 2,4-D in ammonium carbonate is not stable a t a high temperature. Absorbance may be measured, without any appreciable change, after heating to 40" C., beyond which a turbidity appeared. PREPARATION O F STANDARD CONCENTRATION CURVE
Samples containing from 2.11 to 14.75 mg. of thorium were precipitated with 2,4-D, as before. The precipitate] after washing with water, alcohol, and ether, was dissolved in 50 ml. of 0.08111 ammonium carbonate and then diluted to 1 liter with distilled water. The absorbances of such solutions were measured a t 230 mp, against a blank solu-
tion containing ammonium carbonate of the same strength. Results when plotted showed that Beer's law was obeyed through the entire range, The optimum results were obtained in solutions containing from 2 to 14 mg. of thorium per liter. ANALYTICAL PROCEDURE FOR DETERMINATION O F THORIUM
A solution of thorium nitrate containing 2 to 20 mg. of thorium was diluted to 20 ml., adjusted to a pH of 2.4 with 0.01N sodium hydroxide, or hydrochloric acid, and it was heated to 80' C. This solution was precipitated with an excess of hot 1% 2,4-D solution. The white precipitate was allowed to settle for 5 minutes, then filtered with suction through a KO. 3 sintered glass crucible, washed with a 0.1% solution of the reagent, followed by hot alcohol (75%), and finally ether, until it was free from any adhering reagent. The precipitate was then dissolved in 50 nil. of 0.08M ammonium carbonate solution and washed with warm water (40' C.). The resulting solution was diluted to 1 liter in a volumetric flask. The absorbance of this solution was measured in 1-em. cells a t 230 mp, against a reference solution containing the same concentration of ammonium carbonate. The amount of thorium corresponding to this absorbance value was determined from the standard concentration curve. The average molar absorbance index for a set of results has been calculated to be 12.124 (Table 11). Effect of Diverse Ions on Determination of Thorium. Samples were prepared containing a definite quantity of thorium and known amounts of various metals. Precipitation of thorium and its determination by spectrophotometric method were carried out as before (Tables I1 and 111). Iron(I1and 111),cerium(IV), and zirconium interfere seriously. Smaller amounts of other common metals do not intfr-
Figure 1. Ultraviolet absorption spectra
x
Thorium. 7.26 10 - 5 ~ 2,4-D. 17.80 X 10 - 5 ~ Ammonium carbonate. 0.0106M
fere. Estimation of thorium in monazite sands has also been possible. DISCUSSION
Thorium is precipitated completely from its solution with 2,4-dichlorophenoxyacetic acid The thorium salt of this acid is highly soluble in a dilute ammonium carbonate and this solution shows strong absorption in the ultraviolet region of the spectrum, the maximum absorbance occurring a t 230 mp. The absorbance x i s probably caused by the phenyl group of 2,4-D in the thorium salt and not by the thorium carbonate or the ammonium carbonate solution. The amount of ammonium carbonate required to dissolre the thorium salt is not critical. The solution of the thorium salt in ammonium carbonate follows Beer's law and the sensitivity as obtained from that curve, according to Sandell, is 0.019 y. The accuracy is poor in samples of less than 2 mg. of thorium. The molar absorbance index has been found to be 12.124. As thorium may be removed by precipitation from a large number of metals, its determination in their presence has become easier. Iron(II), cerium(IV), and zirconium interfered seriously but
Table 111. Determination o f Thorium in the Presence o f Foreign Ions
Table IV.
in Monazite Tho2 Present, Tho2 Found,
Added", Thorium Found, Mg.
Metals
Rlg.
cu
15
20
Cd A1
20 12 20
Cr Ca
20
Ba 51g Zn
Ce(II1) S i
co
20 15
25 20 20 20
. 6 29
6 34 6 28 6 36 6 30 6 29 6.30
6 28 6.34 6.68 6.71
La(II1) 6.35 Ti 15 6.29 U(V1) 10 6.42 A411 solutions contain 6.32 mg. of thorium.
Determination of Thorium
Monazite (Travancore) Monazite
$0 7.30
so
7.32 7 32
'7.31 4.80
4.75 I78
Department of Chemistry, Bose Research Institute, Calcutta, for the facilities offered to him. LITERATURE CITED
(1) Datta, S. K., ANAL.CHEM.30, 1653 f 19.58). \ - - - - I -
only a slight interference was observed in the presence of nickel, cobalt, and uranium. The method may prove useful for the rapid determination of small amounts of thorium. ACKNOWLEDGMENT
The author is grateful to D. hl. Bose, director, and P. K. Bose, head of the
(2) Datta, S. K., Banerjee, C., Anal. Chzm. Acta 12, 323 (1955). (3) . . Datta. S. K., Baneriee, G., J. Indian Chem. Sbc. 31,397 (1964): (4) Ibid.,p. 773. (5) Ibid., p. 929.
RECEIVED for review June 2, 1958. Accepted September 29, 1958. Work carried out at the Chemical Laboratories of Darjeeling Government College and Bose Research Institute, Calcutta.
Infrared Analysis of the Isomers of N,N- Diet hylto Iua mide WILLIAM
H. CLARK
Research Center, Hercules Powder Co., Wilmington, Del.
b N,N-Diethyltoluamide was found b y the U. S. Department of Agriculture to b e a very good insect repellent. In production samples, i t is o f interest to know the isomer ratio, because the meta isomer is considered the most effective repellent. There are no conventional chemical methods that can b e used to determine the isomer ratio. An infrared spectrophotometric method has therefore been developed. The meta and p a r a isomers are determined by a conventional infrared technique. To determine the ortho isomer, a compensation technique i s used to reduce interference from the meta isomer. The infrared spectra and methods are included.
A
2 years ago, N,N-diethyltoluaniide was found by the U. S. Department of Agriculture to be a very good insect repellent. Because the meta isomer is considered the most efBOUT
fective, the isomer ratio in production samples was investigated (1, 3). There are, a t present, no conventional chemical methods for determining the isomer ratio. An infrared spectrophotometric method may be used to analyze mixtures of N,N-diethyltoluamide. Two procedures are described herein: one for the analysis of mixtures where the meta isomer is high (60 to go%), the para isomer is low (10 to 40%)' and the ortho isomer is absent; and the other, for mixtures where 5 to 10% of the ortho isomer is present. No detectable amounts of interfering components have been observed in production samples. The infrared absorption band at 5.9 microns, which is due to the acid carbonyl group, was used to confirm the absence of toluic acids in the standard as well as production samples. To determine the ortho isomer a compensation technique was used to reduce
the overlapping of the meta absorption on that of the ortho isomer. Although the compensation technique has been known for some time (W), very few methods involving its use have been reported. compensation is very useful when there is overlapping or nearoverlapping absorption, such as with the ortho and meta isomers. Figure 1 illustrates the difficulty of determining 6% of the ortho isomer by a conventional infrared method. The ortho isomer is indicated by a weak shoulder a t 13.70 microns. Figure 2 illustrates the use of a compensation technique to bring out the absorption band for the ortho isomer a t 13.70 microns. There is a tendency to avoid using this technique, because solutions for compensation should be an exact match for a certain component of the sample. In the present case, however, the concentration of the reference solution may VOL. 31, NO. 2, FEBRUARY 1959
197
