CHROMATOGRAM ( A )
CHROMATOGRAM ( A )
Figure 1 . Effect of flash heater temperature on chromatograms of loganberry extract Flash heater: Chromatogram A, 205' C.; chromatogram 6, 100' C.
6
18
24
TIME
x)
(MIN)
56
di L 42
46
Figure 2. Effect of flash heater temperature on chromatograms of a-terpineol Flash heater:
of charged samples were a factor, the area of peak X, identified by infrared spectra as a-terpineol (p-menth-l-en-8-01), would be the reverse of that shown in Figure 1. Comparison of chromatograms A and B of Figure 2 shows that a-terpineol is aImost completely destroyed in A , whereas only slight decomposition was noted in B. The only difference in operating conditions for the two chromatograms was the flash heater tempera-
12
Chromatogram A, 205' C.;
ture. The fact that some decomposition was still evident, even a t 100" C. emphasizes the thermal lability of the compound. Similar results were observed for linalool. Oxygenated terpenes are not peculiar in this respect and, like many compounds, they present a problem in achieving plug flow because of their relatively high boiling points. Evaluation of flash heater temperatures for unknown mixtures, to avoid decomposition, may prove desirable in
chromatogram B , 100' C.
most cases. While low flash heater temperatures tend to give undesirable skewed peaks (Figure 1, chromatogram B ) , these are less objectionable than to devote time to the analyses of thermal artifacts.
E.A. Day
P.H. MILLER Department of Food Science and Technology Oregon State University Corvallis, Ore.
Spectrophotometric Determination of Iron in UraniumFission Efement Alloys SIR: In studies connected with the processing of fuels for the Second Experimental Breeder Reactor (ERB-11)) i t has been necessary to determine less than 0.01% of iron in uranium alloys containing moIybdenum, ruthenium, palladium, rhodium, and zirconium. A simplified procedure for the spectrophotometric determination of iron in metallic uranium reported by Tomida and Takenchi (3) appeared to be adaptable for use on such samples. In Tomida's procedure, iron in a uranyl chloride solution of 7.5N hydrochloric acid was extracted into butyl acetate. After washing the organic layer twice with 7.5N hydrochloric acid, the butyl acetate phase was diluted with 870
ANALYTICAL CHEMISTRY
an equal volume of methyl isobutyl ketone (hexone) and the mixed solvent layer was contacted with a 20% aqueous solution of ammonium thiocyanate. The absorbance of the iron thiocyanate complex was measured directly in the organic solution. A procedure reported by Evans, Hrobar, and Patterson ( I ) utilized an ammonium hydroxide precipitation of uranium and zirconium to separate zirconium from palladium and molybdenum contained in uranium-fission element dloys. Because molybdenum was considered a possible interference in the iron thiocyanate procedure, i t appeared that an ammonium hydroxide precipitation using uranium as a carrier
for iron would serve a two-fold purpose: It would separate the iron from molybdenum and i t would also furnish a precipitate which could be dissolved in 7.5N hydrochloric acid prior to the extraction with butyl acetate. As very little information was available on the details of the Japanese work, a study was made of the absorption spectra of the complex used, the effect of the hexone added, the time required for full color development, and the stability of the colored complex in the organic medium. The absorption spectra displayed a broad maximum centered about 500 mp, Full color development was obtained within 15 minutes and the color
was stable for more than 24 hours. In 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 2.5 2.7 0.25 0.20 0.5 2 1.9 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
