was stable for more than 24 hours. I n the case of the reagent blank, however, the absorbance increased steadily after the first 30 minutes. This appeared to be due to formation of a yellowish brown colloid from the decomposition of thiocyanate in the organic medium. When the iron - thiocyanate complex was formed in butyl acetate alone, the same type of decomposition occurred very rapidly. The addition of hexone prevented this decomposition, perhaps by decreasing the amount of excess thiocyanate which was extracted into the organic mixture. Hydrogen peroxide, added as an oxidant to ensure the presence of iron(III), had to be removed from the butyl acetate phase by scrubbing with hydrochloric acid, or the same type of thiocyanate decomposition occurred. A second reason for using the mixed organics is that it prevents the emulsion problem mentioned by Menis and Rains ( 2 ) . RECOMMENDED PROCEDURE
Pipet a sample containing 2 to 30 pg. of iron into a centrifuge cone containing an excess of ammonium hydroxide. Centrifuge and discard the supernate. Dissolve the precipitate in 5 ml. of 7.5N hydrochloric acid and transfer to a separatory funnel using 5 ml. of 7.5N hvdrochloric acid to rinse the cone. i d d 0.5 ml. of 30% hydrogen peroxide. Add 10 ml. of n-butyl acetate and shake for 1 minute. Scrub the organic phase twice with 10 ml. of 7.5N hydrochloric
Table I.
ua 100
Determination of Iron in Synthetic Solutions Iron, pg. Rh 2; Taken Found?
Foreign Ion Added, Mg. Mo Ru Pd
2.5
20 10 5 20 2.5
20 5 , 19.8 10.4, 9 . 5 4 . 7 , 5.2 20.5 -0.2
0.25
100 100
2.5 2.7 0.25 0.20 0.5 10 9 . 5 , 10.1 0.5 2 1.9 2.5 2.7 0.25 0.20 a 2 mg. of U used as carrier for iron except in those three cases where 100 mg. of U was added. * Daily variation in blank corresponded to +0.4 pg. of Fe. acid. Add 10 ml. of hexone to the organic phase. Contact the combined organics with 20 ml. of 20% ammonium thiocyanate by shaking for 1 minute. After 15 minutes, measure the absorbance of the organic solution us. a reagent blank with a Beckman Model B spectrophotometer in 1-em. cells a t 500 mp. Determine the iron content from a calibration curve. The procedure has been tested on synthetic solutions containing known amounts of uranium, molybdenum, ruthenium, palladium, rhodium, zirconium, and iron and wassatisfactory. The method has also been applied to the determination of iron in unirradiated uranium-5yo fission element alloys used in EBR-I1 melt refining studies. Typi-
cal data on solutions containing known amounts of iron are shown in Table I. LITERATURE CITED
(1) Evans, H. B., Hrobar, A. N., Patterson, J. H., ANAL. CHEM.32, 481 (1960). (2) Menis, O., Rains, T. C., Ibid., 1837 (1960). (3) Tomida, Y., Takenchi, T., Bunseki Kagaku 10,156 (1961). J. J. MCCOWN D. E. KUDERA Argonne National Laboratory Idaho Division P. 0. Box 2528 Idaho Falls, Idaho Operated by the University of Chicago under Contract No. W-31-109-eng-38. Work performed under the auspices of the U. S. Atomic Energy Commission.
Spectrophotometric Determination of Yttrium and Rare Earths in Cast Steels SIR: An investigation of the properties of rare earth alloyed cast steels necessitated a method for the quantitative determination of yttrium and rare earths in the range of 0.01 to 0.1%. The number of samples dictated a relatively simple analytical method which could be carried out on a routine basis. Available equipment suggested a spectrophotometric method. Preliminary precipitation of the rare earths as fluorides has been recommended in solutions containing iron, but with the high iron to rare earth ratio encountered here precipitation would be incomplete ( 1 ) . However, Lerner and Pinto (6) coprecipitated rare earth fluorides and oxalates with a thorium carrier from stainless steel solutions which contained ammonium fluoride and obtained high recoveries. The reagent arsenazo [3-(2-arsonophenylazo) - 4,5 - dihydroxy - 2,7naphthalenedisulfonic acid]has been used for the spectrophotometric determination of rare earths ( 2 , 4, 5 ) . As this re-
agent complexes with thorium to give color interference, any method using a thorium carrier must provide for its subsequent removal. The anion exchange resin Dowex 1-X10 (3) seemed best for the separation of the small quantities of rare earth from thorium. The proposed method consists of the separation of yttrium or rare earth as fluoride from large quantities of iron by coprecipitation with thorium from a solution containing ammonium fluoride. The rare earth is further purified by a second coprecipitation using thorium oxalate as the carrier. The thorium is then separated by anion exchange and yttrium or rare earth determined spectrophotometrically using the colorforming reagent, arsenazo. EXPERIMENTAL
Apparatus. Spectrophotometer, Beckman Model DU, using 1-cm. cells. Ion Exchange Column. A glass tube 10 mm. in diameter X 15 cm. long with
a capillary 2 mm. in diameter is drawn out from the bottom and bent in the shape of a gooseneck measuring 7 em. high. An elongated dropping funnel 15 mm. in diameter X 30 cm. long with the lower end drawn to a 2-mm. diameter constriction is attached to the column by Tygon tubing. A bed of Dowex 1-XlO resin, 3.5 to 4 cm. deep, is held in the glass column by a plug of glass wool. Reagents and Solutions. The following reagents were used: Yttrium, lanthanum, neodymium, and gadolinium oxides, all a t least 99.9% pure (Lindsay Chemical) ; mischmetal, 45% Ce (Mallinckrodt Chemical). Stock rare earth solutions were prepared by dissolving the oxide or metal in 20y0 excess hydrochloric acid and diluting with distilled water to give 500 pg. of rare earth per ml. Ceric ammonium sulfate (500 pg. Ce per ml.) was dissolved in water containing a trace of ascorbic acid. Thorium(1V) nitrate, tetrahydrate, c.P., was used without further purification. Correction for rare earth content was made by carrying out blank deterVOL. 34, NO. 7, JUNE 1962
* 871
minations. Dowex 1-X10 anion exchange resin, ionic form C1-, 200- to 400-mesh, reagent. The resin was conditioned for use in thorium separations as described by Faris (3). Arsenazo, 0.1% solution prepared from 3 - (2 - arsonophenylazo) - 4,5 - dihydroxy - 2,7 - naphthalenedisulfonic acid, disodium salt. (Eastman) Procedure. Fluoride and Oxalate Precipitations. Dissolve the steel sample in sufficient 1:1 concentrated hydrochloric nitric acid mixture (a 1-
/
Table 1. Analysis of Synthetic Yttrium or Rare Earths-S.A.E. 8630 Steel Mixtures
Repg. covery, Rare Earth Taken Recovered % Y 42 35" 83 83 72a 87 104 92a 88 40 37 93 Gd 20 20 100 43 35a 81 200 188 94 40 39 98 Mischmetal 20 17 85 20 19b 95 100 77 77 40 32 80 80 72 90 200 176 88 200 185 93 La 100 87 87 Ce 80 81 101 Nd 100 76 76 Mean 89 Std. dev. ~ t 7 . 3 Fluorides were precipitated from 5 ml. of solution containing 0.2 g. of dissolved steel control sample except, a contained no dissolved steel b contained 0.1 g. of control sample. pg.
Table II.
Heat No. 11 D
Rare Earth Present Y
4D
1026
Y
16 D
8630
Y
19 D
8630
Gd
a
8630
Mischmetal
8630
Mischmetal
Contained O.O060j, boron.
872
,
,
EliiT,
- __ u *
w-
,
Figure 1. Calibration curves for yttrium and rare earth arsenazo color complexes A. yttrium 8. mischmetal C.
gadolinium La, Ce, N d curves lie between curves B and C
gram sample requires about 10 ml. of the acid mixture). Add 10 ml. of 707, perchloric acid per gram of sample and heat to near dryness. Transfer a 5or 10-ml. aliquot of steel solution containing 10 to 200 pug. of rare earth to a 15-ml. polypropylene centrifuge tube. Add 0.5 ml. of solution containing 25 mg. of thorium nitrate tetrahydrate. Add 0.2 ml. of 48Y0 hydrofluoric acid and 50 mg. (approx.) of solid ammonium fluoride. Heat the mixture to near boiling for 1 hour, or until the precipitate has become granular. Centrifuge, and wash the precipitate with 5 ml. of 17, ammonium fluoride solution. Dissolve the precipitate in a mixture of 5 ml. of concentrated nitric acid and 50 mg. (approx.) of solid boric acid. Transfer the solution to a beaker using warm water to dissolve the excess boric acid. Evaporate the solution t o near dryness. Extract the residue by heating with 5 ml. of miter
70 Rare Earth 0.072
0,064 0.087
0.083 0.038 0,035 0.033 0.020 0.016
ANALYTICAL CHEMISTRY
Average % Rare Earth
Standard Deviation
0.068
S O . 004
0.085
10.002
0.035
f0.002
0.018
10.002
0.035
*0.001
0.064
10.002
0.035 0.034
13 D
,
R"S
Replicate Determination of Rare Earths and Yttrium in Cast Steels
S.A.E. No. 1027
15 D
,
-i_
0.036 0.064 0.062 0,066
and allowing the condensing vapors to wash down the sides of the beaker for 5 minutes. Boric acid adhering to the beaker and cover glass need not be completely dissolved. Transfer the solution to the same polypropylene centrifuge tube with 5 ml. of methanol. Heat to about 60' C., add 0.5 ml. of saturated oxalic acid solution, and continue heating for 1 hour longer. Cool for 30 minutes or longer and centrifuge. Kash the precipitate with 5 ml. of 1% oxalic acid in 1:l water methanol mixture. Thorium Separation. Dissolve the oxalates in 5 ml. of concentrated nitric acid and transfer the solution to a beaker using concentrated nitric acid to give a total volume of 15 to 20 ml. Add 5 drops of 70% perchloric acid and evaporate to the appearance of dense white fumes. Dissolve the residue in 5 ml. of 8M nitric acid. If the solution is not clear, add 2 to 3 drops of 70% perchloric acid and evaporate to fumes again. Transfer the clear solution to the anion exchange column. Wash the rare earth from the column with 20 ml. of 8J1 nitric acid. Evaporate the eluate to dryness and bake to eliminate nitric acid. Add 1 ml. of concentrated hydrochloric acid and evaporate t o dryness on a steam bath. Dissolve the rare earth residue in 5 ml. of 0.0131 hydrochloric acid. Spectrophotometric Procedure. Transfer the rare earth solution to a 25ml. volumetric flask. Add 10 drops of freshly prepared '20% hexaniethylenetetramine solution and 2 nil. of 0.17, arsenazo. Dilute to volume with water. Read the absorbance a t 580 mp against a reagent blank. Obtain the rare earth content from a plot of absorbance us. pg. of rare earth. (Figure 1.) RESULTS AND DISCUSSION
To establish the accuracy of the method, determinations were carried out on aliquots of solutions of pure yttrium and gadolinium oxides and on mischmetal. with and without the presence of control steel samples. Results are shown in Table I. The precision of the method is indicated by the standard deviation of the recoveries shown in Table I and by the results of replicate analysis of steel samples containing yttrium or rare earth shown in Table IT. For the mischmetal results in Table 11, triplicate aliquots of a solution of a single steel sample were taken for analysis. For the yttrium and gadolinium different drillings from the same ingot were selected. Recovery in the present method (897,) is lower than that reported by Lerner and Pinto (96% to 9 7 7 3 , who used an 8-quinolinol evtraction of thorium to separate rare earths. The difference can be accounted for by loss of rare earth by retention in the ion exchange column. Recoveries of known quantities of yttrium and gadolinium (100 pg.), used in preliminary column recovery experiments, averaged 93%.
This amount was recovered in the first 25 ml. of effluent. Only traces could be detected spectrophotometrically in the next 25 ml. of effluent, after which blank increases due to thorium were noted. KO loss of rare earth occurred in the steps after the ion exchange. By the procedure described here, 6 to 12 determinations may be conveniently carried out simultaneously in 12 to 14 hours. The coprecipitation and separation procedures of Lerner and Pinto (6) have been adapted to allow the use of both smaller samples and equipment. The method appears to be applicable to many other steels where interfering ions would have soluble fluorides and oxalates.
ACKNOWLEDGMENT
The authors thank the Riverside Foundry Division of Sivyer Steel Co., Bettendorf, Iowa, for supplying the base steels used in this study. Appreciation is extended t o the Lindsay Chemical Division, American Potash and Chemical Corp., West Chicago, Ill., for supplying the rare earth oxides used for calibration purposes. LITERATURE CITED
U. S. A., by the Israel Program for Scientific Translations. 1960. Pages (original) 162-75. Pages (translation) 177-90. (2) Banks, C. V., Thompson, J. A., O’LaughCn, J. W., ANAL. CHEM.30, 1792-5 (1958). (3) Faris, J. P., Appl. Spectroscopy 12, 157-61 (1958). (4) Fritz, J. S., Richard, Marlene J., Lane. W. J.. ANAL.CmM. 30. 1776-9 (1958). --, ( 5 ) Kuteinikov, A. F., Lanskoi, G. A., Zhur. Anal. Khim. 14,686-90 (1959). (6) Lerner, M. W., Pinto, L. J., ANAL. CHEM.31,549-51 (1959). > -
~
(1) Alimarin, I. P., Paviotskaya, F. I.,
Akademiia Nauk S.S.S.R. Inst. geokhimii i analitic9koi khimii. “Rare Earth Elements, Washington. Published for the National Science Foundation and the Department of Commerce,
BERNARD J. BORNONG JOHN L. MORIARTY Lunex Co. Box 196 Pleasant Valley, Iowa
Titrimetric Determination of Some Amine Oxides and Phosphine Oxides in Acetic Anhydride SIR.Amine oxides have been determined by reduction with stannous chloride (9) and with titanium(II1) ( 1 , 4 ) . Amine oxides, in general, are not sufficiently basic in glacial acetic acid to permit titration with perchloric acid. This is also trde of the phosphine oxides (6). Some heterocyclic N-oxides undergo irreversible reduction at the dropping mercury electrode (9); however, a direct approach to purity is more desirable. Formation of a chromophore with dimethylaniline has been proposed for the detection of amine oxides (2). No attempt has been made to quantitate this reaction. A red or reddish brown color is reportedly produced when amine oxides are treated 11-ith acetic anhydride (7’). Acetic anhydride has been demonstrated to be the solvent of choice for the titration of certain very weak bases (8, 10, 11). During the investigation of the basicity of some S-oxides, trimethylphosphine oxide was found to exhibit very sharp inflections in acetic anhydride when titrated with perchloric acid. This work has been extended to include other phosphine oxides and a number of heterocyclic amine oxides. This method is probably applicable to aliphatic, alicyclic, and aromatic amine oxides, also; however, pure representative samples of these mere not available. EXPERIMENTAL
Apparatus and Reagents. A Precision-Dom Recordomatic titrator, Model K-3-247, was used in all titrations. The modified calomel-glass electrodes and reagents used are described elsewhere (10, 11). For best
results the electrodes should be equilibrated continously in acetic anhydride when not in use rather than the 12-hour immersion period previously specified. Procedure and Results. An approximately 0.001 mole sample, accurately weighed, is dissolved i n 100 ml. of acetic anhydride with stirring
Table I. Titration of Amine Oxides and Phosphine Oxides in Acetic Anhydride
Sl,
Compound Purity TV-Methyl-bis(2-hydroxyethy1)amine oxide 89 .Oa Nicotinamide 1-oxide 44. 8b 2,6-Dimethylpyridine N-oxide 99.6 99.0 Pyridine N-oxide 96.7 97.lC 100.4c 100.6d 2-Methylpyridine N-oxide 97.5d 4-Cyanopyridine N-oxide 100,4 99.8 4-Hydroxyquinazoline 3-oxide 95.8 97.1 4-Hydroxy-3-imino-l,2,4-
benzotriazene 1-oxide PNitropyridine N-oxide
99.4 101 .o 100.2 Trimethylphosphine oxide 100.1e Tri-n-octylphosphine oxide 96.6 96.4 Triphenylphosphine oxide 94.9 95.6 a Impure sample, exhibited two inflections indicating presence of parent amine. b Incompletely soluble in acetic anhydride. c Irregular titration curves. d Irregular titration curves, titration in acetonitrile gave a value of 100.2%. e Reference ( 1 1 ) .
and then titrated with 0.1 N perchloric acid i n dioxane. All samples were analyzed as received without further purification. The results are shown in Table I. DISCUSSION
Polonovski observed the exothermic reaction of aliphatic amine oxides with acetic anhydride to produce an aldehyde and a secondary amine (7‘). This reaction reportedly accompanied by a reddish brown color was not noted among the compounds reported here. Although the results for pyridine 1-oxide were quantitative, the titration curves were somewhat irregular, indicating the possibility of a side reaction. Acetic anhydride is said to convert 1-oxides (without a n alkyl group alpha to the K +- 0) into pyridones (6). No explanation can be given for the anomalous behavior of 2-methylpyridine 1-oxide. Triphenylphosphine oxide exhibited a distinct inflection; however, i t was much less sharp than the corresponding trimethyl compound. The decreased basicity observed is due to the electronegativity of the aromatic rings. The nature of the substituent as well as its position relative to the amine oxide group will affect the sharpness of the inflection. The polar nature of amine oxides favors solubility in acetic anhydride; however, nicotinamide 1-oxide was only partially soluble. All other amine oxides examined were freely soluble . ACKNOWLEDGMENT
The author thanks J. A. Carbon and VOL 34, NO. 7, JUNE 1962
873
