Spectrographic Determination of Rare Earth Elements in Uranium Compounds ROBERT C. HIRT' AND NORMAN H. NACHTRIEBa Unicersity of California, Los Alamos Scientific Laboratory, Santa Fe, N.
M.
To avoid interference from uranium lines in the spectrographicdetermination of rare earth elements in uranium compounds, the uranium is removed chemically by an ether extraction, precipitation as fluorides, and purification by way of the hydroxides. The final determination is carried out spectrographically by the copper-spark method. Seven rare earth elements were investigated and their limits of detection (sensitivity) and recoveries from UaOs are reported.
were performed, using a 125-ml. separatory funnel and 1 ml. of water each time. The water layers were combined and evaporated nearly to dryness. Five milliliters of concentrated nitric acid solution of all material. added to The rare earth elements mere precipitated with 20 ml. of 48% hydrofluoric acid in a platinum evaporating dish. The precipitate was allowed to digest for several hours or overnight. After filtration of the fluoride precipitate on No. 42 Whatman paper, the paper and residue were ignited in a platinum crucible. Conversion of the rare earth fluorides to sulfates was accomplished by twice fuming the ignited residue to dryness with 0.5-ml. par-
HE spectrographic determination of the rare earth elements in uranium compounds lacks sensitivity and is uncertain because of the large number of lines contributed by the uranium spectrum. To avoid the presence of these uranium lines a chemi,tal separation of the rare earth elements from the uranium was performed before the spectrographic analysis, The spectragraphic procedure used was essentially that of the copper-spark method (1). The chemical separation was obtained by means of an ether extraction of uranyl nitrate, precipitation of the rare ,earths as fluorides, and further precipitation as hydroxides, as proposed by Short and Dutton ( 2 ) .
t l o ~ ~ ~ ~ ~ ~ ~ ~ acid ~ ~and ~the ~ ~ droxides of the rare earth elements were precipitated with 20 ml. of concentrated ammonium hydroxide and 5 grams of salicylic acid. Five or six washings with 5% ammonium hydroxide w'ere necessary to remove the last traces of uranium. If multiple washings failed to remove the yellow color entirely from the filter paper, the precipitate was redissolved in hydrochloric acid and another precipitation of the hydroxides carried out. The precipitated hydroxides were dissolved in 0.3 ml. of 6 N hydrochloric acid and the solutions transferred with micropipets to the tops Of copper mm. in diameter for evaporation t'o dryness thereon, by heating with a small electric heater coil.
PREPARATION OF SAMPLE?
If not already in the form of uranyl nitrate, the sample was treated with nitric acid and evaporated Slowly to dryness. Tengram samples were commonly used. The nitrate was dissolved in a minimum amount Of anhydrous ether and three extractions 1 Present address, Physics Division, Stamford Research Laboratories, American Cyanamid Co., Stamford, Conn. Present address, Institute for the Study of Metals, Cniversity of Chicago, Chicago 37, Ill.
*
Table I. Element La
Ce
Pr
Sd
Sm
Gd
DY
The chemical separation was essentially that proposed by Short and Dutton ( 2 ) ,but with several modifications to eliminate the last traces of uranium. The extra ether-water extractions, the second treatment of the ignited fluoride precipitate with hot sulfuric acid, and the multiple rinsings of the precipitated hydroxides Jyith 5% ammonium hydroxide served to eliminate the troublesome uranium background on the spectrographic plates. The multiple rinsings were carried out until the yellow color was eliminated, or the hydroxides were reprecipitated.
Wave Lengths and Sensitivities of Rare Earth Elements Wave Length A. 3949.11 3988.52 3871.63 3794.77 3790.82 4151.97 4012.39 3801.53 4137.65 4186.60 4100.75 4008.71 4179.42 41 18.48 4189.52
Sensitivity Microorams P.p.m. 0.01 0.05 0.05 0.10 0.10
0.001 0.005 0.005 0.010 0.010
0.10 0.20 0.20 0.50 0.50
0.010 0,020 0.020 0.050 0.050
0 1 00 0 .. 1 0.20 0.20 0.50
4012.25 3851.75 4303.57 3863.41 3592.59 3745.69 3634.27 4256.40 3568.26 3422.47 3100.51 3362.24 3350.10 3481.82
0.20 0.20 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.05 0.05 0.05 0.10 0.10
0.010 0.010 0.020 0.020 0,050 0,020 0.020 0.050 0,050 0,030 0.050 0.050 0.0.50 0.050 0,005 0.005 0.005 0.010 0.010
3531.71 3577.99 3407.80 3538.52 3393.58
0.05 0.05 0.05 0.10 0.20
0,005 0.005 0.005 0.010 0.020
SPECTROGRAPHIC PROCEDURE
A Jarrell-Ash IadsLvorth automatic spectrograph having a dispersion of 5.27 A. per mm. nvas used to carry out the determinations. The copper electrodes were placed 45 em. from the slit, with a 90-mm. spherical quartz lens 37 em. from the slit, Tvhich was 35 microns wide and 2 mm. high. Eastman Spectrum Analysis No. 1 plctes were used for photographing the region from 2100 to 4000 A. Standard solutions of lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and dysprosium of a concentration of 100 micrograms per ml. were prepared and were diluted to make solutions of 10 and 1 microgram per ml. concentration. Suitable amounts of these solutions were transferred by micropipets and evaporated on the freshly machined flat ends of copper electrodes 6 mm. in diameter. These were made the bottom electrodes in the spark. An A.R.L.-Dietert Alultisource operating off a 230-volt alternating current line a t 19 amperes (primary) was used as power source. Sixty microfarads of capacity, 25 microhenries of inductance, and 25 ohms of resistance were used in the spark circuit. The spark was operated a t 920 volts with an initiator a t 10,000 volts. Exposures were for 40 seconds. The spark was found to be very stable and the exposures were reproducible. This spectrographic procedure is essentially that of the copperspark method ( 1 ) . The exposed plates were developed in Eastman D-19 developer 1077
'
~
~
~
1078
ANALYTICAL CHEMISTRY
Table 11.
Recovery of Rare Earth Metals from Us08
(Summary of several tests on 10-gram samp!es) Micrograms Micrograms R e m \ ered Element Added hlin. Max. La 2.0 2.0 1 .o 0.7 1.0 Ce 2.0 1.5 2.0 1.o 0.8 1.0 Pr 2.0 1.2 2.0 Nd 5.0 4.0 5.0 1 .o 0.7 1 .o 0.5 0.3 0.5 Sm 5.0 4.5 5.0
Gd DY
1.o 5.0 1.o 0.5 5.0 1. o 0.5
4.5
The wave lengths of the lines used are given in Table I along with the limit of detection (sensitivity) of the element in niicrograms and in parts per million, based on a lO-granl sample. The lower limits of detection reported, in comparison to those of Short and I h t t o n are probably due to the greater sensitivitv of the copppr-spark method (1).
0.8
RECOVERIES
d.0 1.0
Tests on recoveries were made by adding known amounts of the rare earth elements to lO-gram samples of I.7308, which aere subjected t o the separation procedure and the spectrographir analvsis as described. Some typical recoveries are shoir-n in Table 11. Because these data are taken from several such tests, the number of micrograms recovered are reported betweerr the upper and lower limits found.
0.4
0.5
3.0
3.0 1.0 0 ,s
0.3
ured intensities were compared to the graph to determine the amount of the element present in the sample. The more precise method of using internal standards and working curves of log intensity us. log concentration \vas not used for reasons of economy of time and lack of need for any greater accuracy.
for 3 minutes, placed in an acetic acid short-stop bath for 10 seconds, and fixed in acid sodium thiosulfate for 5 minutes. They were dried in a stream of warm air. A standard plate nas prepared using 5 , 2 , 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01, and 0.005 microgram of each element. The selected lineb n ere photometered on an A.R.I,.-Dietert projectioncomparator denhitometer. Per cent transmittance measurements viere made of the selected line and the immediate background, and were convei ted to relative intensities, before correcting for the background. A plot of corrected intensities against quantitj of element piesent n a s made. Plates fiom samples \\'ere prepared in the same inaiiner, and several si andai dh wrc' photographed on wc-h plate. T h r mea+
LITERATURE CITED
(1) Fred, >I., Narhtrieb, N. H., and Tomkins, F.S., J. Optical SOC. Am.. 37, 279 (1947). (2) Short, H. G., and Dutton, W. L., A N ~ LCHEY., . 40, 1073 (1948). RECEIVEDSovember 25, 1947. This paper is based on work performed during 1944 a t the Los .ilamo$ Scientific Laboratory of the University of California under Government Contract W-7405-eng-36 and t h e information contained therein will appear in Division V of the National Suclear Energy Series (1Ianhattan Project Technical Section) as part of the contribution of thr 1.04 .\lamas Lahoratory.
Determination of Methyl Allyl Chloride Recovery f r o m Fumigated Grain SH4FIK 4LI EL KFIISEIEY, Furuk I University, College of .Igriculture, .-ilexundria, E g y p t The most important properties and reactions of methyl all31 chloride are discussed and the possibilit3 of their use for its quantitative determination is fully investigated. A bromine absorption method has been successfully developed for the determination of the compound as a liquid, of the concentrations of its tapor in air in fumigation processes, and of the tapor retained by fumigated grain. Procedures for the recouerj of the fumigant have been devised and successfull? applied for the complete recover? of the fumigant from grain.
.
ETHYL allyl chloride was first mentioned as an insecticide in 1938 by Briejhr ( 2 ) ,~ h communicated o further information a t the 7th International Congress of Entomology in Berlin, 1938. Vaughan and Rust (la)prepared it by the reaction of chlorine and isobutene at 70" C. Later Briejhr (1) found that it was a highly active gaseous fumigant and investigated the distribution of the gas in empty spaces and in fumigated grain and soil, using insects. The change in mortality n i t h degree of exposure to the gas gave a rough estimate of concentration in different parts of the space or at different depths of fumigated substances or in soil. Although Briejkr's work was the first of its kind, it did not touch the chemical part of the problem. .ICcurate methods of determination of the compound had, therefore, t o be worked out. Methyl allyl chloride, methallyl chloride or 3-chloro-2-methylpropene, has the folloaing formula: CH,=C-CH,CI
I
CHI and is a colorless liquid with a strong odor characteristic of allyl compounds. It boils a t 72' C. and its specific gravity at 20' C.
is 0.925. The liquid is volatile, and its latent heat of evaporation a t 20" C. is 89 calories per gram. It is soluble in most organic solvents but not appreciably soluble in water. METHODS OF DETERMIKATION
.ittempts nere made to use the most important reactions of the compound for its quantitative determination. These reactions are hydrolysis, oxidation, and halogenation. Seither hydrolysis with alcoholic potassium hydroxide nor oxidation with dichromate and sulfuric acid appeared to give quantitative recovery of chlorine. The failure of both methods may be due to the volatility of the compound, the fact that was rcqponsible for some loss during the process of analysis. Many procedures for the determination of olefinic unsaturatioii by means of halogen titration make use of the addition reactions of the halogens. Kaufniann (6) was the first to try to regulate the halogen action in such a Kay as t o confine it to addition reaction. The methods of Hub1 (4),Wijs (13, 1 4 ) , and Hanus (,9) gave unsatisfactory re.ultb. hut those of Rosenmund and Kuhnhenn (11) and Kaufmann (.? pave very satisfactory results; $0 their
