were plated for 15 minutes. The results of this experiment are given in Table 11. Here, although the volume and chloride concentration varied by a factor of nearly 7 , the amount of plutonium deposited varied only 16%. Even for the large electrolyte volume the plutonium yield is acceptable. The deposit formed by the plating procedure is assumed to be of the type described by Hufford, Scott, and others (9-4). During the deposition a hydrous oxide is formed in the basic region near the cathode. When the solution is made ammoniacal, the hydrous oxide film becomes fixed to the disk. Upon flaming, this film is converted to an oxide. CONCLUSIONS
Based on the above experiments the following conditions have been chosen for standard operations: volume of solution, 4 to 5 ml. a t p H about 1; chloride concentration, 0.1 to 0.2 gram per ml.; plating time, 15 minutes.
I n practice, the actinide t o be plated is evaporated to dryness several times a i t h hydrochloric acid. The residue is taken up in 1 ml. of hydrochloric acid and the solution transferred to the plating cell with two 1-ml. water washes. Methyl red is added, and then ammonium hydroxide, until the solution is basic. The solution is then acidified with 2-47 hydrochloric acid. This procedure gives a plating bath of the desired volume and concentration. The plating cell is set up on the electroanalyzer and the stirring anode is adjusted to approximately 5-mm. distance above the platinum disk. Voltage is set t o give a starting current of 2 amperes. Radioautographs show that, if the stirrer is set closer than 5 mm., the activity tends to concentrate toward the outer area of the disk. Because of the rapid evolution of hydrogen a t the cathode, this plating would not produce adherent films of actinides in the micro- or milligram region. With tracer quantities, however, very clean adherent deposits are produced. I n many cases it is difficult
to distinguish the plated platinuni from new platinum. This plating procedure offers R rapid method for depositing the actinide elements a t tracer concentrations in high yield. The conditions can be wried over a wide range of volume and chloride concentration without adversely aifecting the yields. LITERATURE CITED
(1) Chopin, -4., University of California
Radiation Laboratory, Berkeley, pri-
vate communicat,ions. 19.56.
( 2 ) H-eord, D. L., Scott; B . F., “Transuranic Elements,” NNES, IV-14B Part I, p. 1149, McGraw-Hill, New York, i949. (3) KO, R., h’ucleonics 15, No. 1, 72 (1957). (4) Rulfs, C. L., De, A. K., Elving, P. J., J. Electrochem. SOC.104, 80 (1957). (5) Went,zler, H. L., private communications, 1956. (6) Wingerson, R. C., private communication to L. F. Tischler, 1953.
RECEIVED for review November 10, 1958. Accepted November 12, 1959. Division of Analytical Chemistry, Symposium on Radiochemical Analysis, 133rd Meeting, ACS, San Francisco, Calif., April 1958.
Separation of Magnesium from Sodium and Potassium A Tracer Study ARNO H. A. HEYN, Department o f Chemistry, Boston University, Boston, Mass. HARMON L. FINSTON, Nuclear Engineering Department, Brookhaven National laboratory, Upton,
The production of magnesium-28 by pileproduced tritons simultaneously results in considerable sodium-24 contamination. The development of a routine chemical processing method for the production of pure magnesium-28 suggested a study of the separation of magnesium and sodium; the ready availability of both of the y-emitting isotopes, sodium-24 and potassium-42, led to further investigation to include potassium. The degree of contamination was determined for magnesium precipitates obtained by precipitating magnesium ammonium phosphate, magnesium oxalate from homogeneous solution, and magnesium-8-quinolinolate both by the conventional method and from homogeneous solution. The extent of sodium and potassium coprecipitated decreased in the order: phosphate method (single precipitaphosphate method (double tion) oxalate method precipitation) quinolinolate method quinolinolate method from homogeneous solution. In this last case the amount of sodium coprecipitated per 69 mg. of mag-
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ANALYTICAL CHEMISTRY
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nesium ranged from 0.02 to about 1 y for 0.4 to 4000 mg. of sodium added. Adsorption is believed to b e responsible for the contamination in most cases. The results presented show the quantitative accuracy and reproducibility of a new magnesium-8quinolinolate procedure for precipitation from homogeneous solution.
T
production of 21-hour magnesium-28 from magnesium-26 by a triton in-neutron out reaction (16) has renewed interest in the separation of sodium from magnesium. The magnesium used contains traces of sodium; also, sodium-24 can result from the following interactions: magnesium-24, neutron in-proton out; magnesium 25, triton in-deuteron out. Because the tritons are produced by a neutron irradiation of lithium-6 giving tritons and alpha particles, sodium-23 present gives the 15-hour sodium-24. Thus, the activity of sodium-24 produced will be significant because of long irradiation times and possible reactions involving the various magnesium isotopes. HE
I. I., N. Y.
The half lives of sodium-24 (15.0 hours) and magnesium-28 (21.3 hours) and the p- and y- energies (14, 15) are sufficiently similar to make differentiation difficult. While there are no feasible procedures for precipitating sodium quantitatively without also precipitating magnesium, several methods supposedly constitute a separation of magnesium from alkali metals. The classical method for determining magnesium is the precipitation of hydrated magnesium ammonium phosphate, but there has been no conclusive examination of the contamination of the precipitate by alkali metals. Previous workers (8,IO) have deduced the amount of alkali metal coprecipitated with magnesium from the errors in the gravimetric phosphate procedure. A possible compensation of errors makes the direct determination of the coprecipitation errors desirable. Other methods are the precipitation of magnesium-8-quinolinolate, and the precipitation of magnesium oxalate in 85% acetic acid. According to Moser
and Scliutt ( I S ) tlte ~nagiimiuiii-Squinolitiolate method gives a complete separation from alkali metal salts, but no conclusive data are given. Llving and Caley ( 3 ) investigated tlie prccipitation of niagnesiuiii osalate in 8570 acetic acid solution. They obtained slightly high resulk for iiiagiiesiutii in single precipitations in the presence of various amounts of alkali metal salts, especially lithium salts. Gordon and Caley ( 4 ) modified the oxalate method by precipitating the magnesium oxalate froni homogeneous solution by the hydrolysis of ethyl oxalate. The use of this method should decrease errors due to coprecipitation because of the lower degree of supersaturation which exists in solution. In the present investigation magnesium was precipitated in the presence of sodiuni salts containing sodium-24 or potassium salts containing potassium42. 'I'hese y-emitting isotopes could be used for determining the amounts of sodium or potassium carried by the precipitatce using conventional tracer techniques. T o improve the magtiesium-8-quinolinolate iiiethod further a procedure of precipit:ition from homogeneous solution was developed. The 8-quinolinol reagent is added to the magnesium solution a t a low pH; then, on raising the p H b>- the hydrolysis of urea (27),most of the magnesium chelate n-ill precipitate. A t this p H of about 7.7 (niasimum attainable by hydrolysis of urea under these conditions) 1.5% of the magnesiiuii will remain unprecipitated, howevci', and ammonium hydroside must be added to raise tlie p H further and precipitate the remaining magnesium chelate. The magnesium chelate so obtained eshibits a noticeably larger particle size than that precipitated in the coiivcntional manner. Photomicrographs of the precipitates are shown in Figure 1. After agitation the precipitate settled in less than 1 minute, whereas that obtained by the conventional method required more than 5 minutes for settling. The amounts of sodium and potassium carried are even lower than those for the ordinary precipitation of the the magnesium chelate. Inasmuch as the quantitative aspects of the previously published procedures hare been worked out in detail, no special efforts were made in this work to obtnin highly precise results for magnesium. It was thus possible to take portions of the precipitates for counting of radioactivity a t various stages during the procedure and to determine the contamination by sodium and potassium as a function of time. Magnesium-28 was used in a few representative runs to determine the aniount of magnesium in the filtrate. Less than 0.2 mg. for 70 nig. of magnesium escapes precipitat,ion by the phos-
phate, homogeneous oxalate, convcntional8-quinolinolate, and homogeneous 8-quinolinolate methods. APPARATUS
The samples were counted in a thallium activated sodium iodide yscintillation well-type counter 2 x 2 inches with 6/8 X 11i2inch well connected to an Atomic Instrument Co. lModel 1050A scaler through a linear amplifier ( 2 ) with the selective input sensitivity set at 0.1 volt. A few countings were performed with an end-window Geiger tube connected to a Suclear Corp. Model 162 scaler. The isotopic purities of sodium-24, potassium-42, and magnesium-28 were checked by y-ray gray wedge pulse height analysis (1)and by comparing the energies of prominent peaks obtained with known standards. This was repeated with a magnesium ammonium phosphate precipitate containing the coprecipitated isotope, with no significant difference in the gray wedge picture. Pictures taken again after several half lives to detect the possible presence of longer-lived isotopes showed no other isotopic impurities, except for magnesium-28, which contained a small trace of a long-lived ?-emitter. PREPARATION
OF MATERIALS
The alkali-metal activity needed for each determination was on the order of 10 to 50 pc., inasmuch as the amount of alkali metal carried by some of the precipitates was espected to be small. SODIUX-24. A 1-hour irradiation of 0.1000 gram of sodium carbonate, anhydrous analytical reagent grade, in quartz was carried out in the Brookhaven National Laboratory reactor a t a neutron flux of about 10l2neutrons cm.+ second-'. After dissolving the irradiated sodium carbonate and diluting to 1000 ml. using a lead-brick shielded facility to permit handling from 1- to 2-foot distance, the solution contained 0.04339 mg. of sodium per ml. and gave 3 X lo8 y counts ml.-l min.-' in the counter extrapolated to the time of removal from the reactor. The decay, followed over a 3-day period, yielded a half life of 14.9 i 0.15 hours [reported half life is 15.06 hours (15)]. For work with higher sodium levels 1.OOO gram of the same sodium carbonate was irradiated for 15 minutes as above, dissolved, and diluted to 100 ml. This solution contained 4.339 mg. sodium per ml. and gave 9.5 X lo7 y counts m1.-1 min.-l. POTASSICM-42. The radioactive potassium rn as similarly prepared by irradiating 1.3820 gram of anhydrous analytical reagent grade potassium carbonate for 15 minutes. The material was dissolved and diluted to 100 ml. This solution contained 7.819 mg. of potassium per ml. and gave 4 x 106 y counts ml.-' min.+ at the time of removal from the reactor. The decay was followed for 2 days and had a half life of 12.6 hours [12.44 hours reported ( f l ) ] . Pulse height analysis (1) gave no evi-
dence for the prcsence of radioactive impurities. RIAGNESIUJISTANDARDSOLUTIOK. Triple-distilled magnesium (1.7147 grams) was dissolved in hydrochloric acid and diluted to 250.0 ml. This solution contained 6.859 mg. of magnesium per ml. Spectrographic analysis showed the presence of only very minor amounts of impurities which were near the low cr detection limits of the spectrograph. MAGNESIUhf-28 SOLUTION. A SOlUtion containing 0.04 pc. of magnesium28 per ml. was obtained from Brookhaven National Laboratory. This solution contained a total of 1.8 mg. of magnesium per ml. The half life was 22 hours [21.3 hours reported ( I C ) ] . Gamma-scintillation gray wedge analysis disclosed no significant radioactive impurities. After 12 half lives only 40 counts min.-1 of a long-lived radio active impurity were noticed. All other reagents were of analytical reagent or ACS grade and were used without further purification. The ethyl oxalate, fresh from stock (Matheson Coleman & Bell), was used without further treatment. PROCEDURES
Precipitation of Magnesium Ammonium Phosphate. T h e procedure given b y Kolthoff and Sandell (12) was followed. Essentially equivalent procedures are given in most other textbooks. All precipitations were carried out using an aliquot containing 68.59 mg. of magnesium and adding the desired amounts of the radioactive tracer solution sodium-24 or potassium-42, respectively. After dryingat 105°C.small weighed portions of the precipitate were transferred to l/* X 3 3 / 4 inch Lustroid tubes (Fisher Scientific Co., Catalog KO. 5-566A), and 2 ml. of 6'37 hydrochloric acid were added to dissolve the precipitate and to collect the radioactive materials in the bottom of the test tube which will be in the well of the scintillation crystal. The counting rate was determined. A high geometry was obtained. A suitable aliquot of the tracer solution diluted to 2 ml. was also counted, thus eliminating errors due to the relatively short half life of the isotope. The amount of alkali metal contained in the precipitate was calculated from the known concentration of the tracer solution and the known fraction of the total weight used. Reprecipitations were carried out in many cases and the same counting process R as repeated. Precipitation of Magnesium Oxalate from Homogeneous Solution. T h e procedure of Gordon and Caley (4) was followed in detail; precipitation and the subsequent counting were carried out as above. Precipitation of Magnesium-8Quinolinolate. T h e procedure of H a h n (6, 7 ) was slightly modified in view of the fairly large amount of magnesium present. His procedure recommends the use of a lY0 solution of VOL. 32, NO. 3, MARCH 1960
329
&quinolinol in 2N acetic acid. For 70 mg. of magnesium about 85 ml. of the reagent solution would have to be added. Because the pH is lowered by this large amount of acetic acid, a fairly large amount of ammonium hydroxide is required to make the solution slightly alkaline. An ethyl alcohol solution containing 5 grams of 8-qninolinol in 100 ml. of solution was used and the volume NaS kept fairly large to offset the solvent action of ethyl alcohol on the chelate. Procedure. Add 2 grams of ammonium chloride t o 100 t o 200 ml. of the solution containing the magnesium and enough filtered 6N ammonium hydroxide t o bring t h e p H t o 9 t o 10 (use narrow range p H papers). Heat to 70' to 80' C., and add slowly a 5% solution of 8-qniuolinol in ethyl alcohol until the supernatant solution is slightly yellow, indicating a slight excess. Digest 10 minutes on the hot plate without boiling, filter, transfer, and wash with approximately 50 ml. of hot water. Dry at 105' C. to the dihydrate or at 150" C . (1 to 1'/2 hours) to the anhydrous compound. Precipitation of Magnesium-& Quinolinolate from a Homogeneous Solution. T h e p H was.raised to the required value by the hydrolysis of Urea (17). During this work it was observed t h a t the darkening of the precipitates, presumably due t o oxidation, could be prevented by the addition of a small amount of ammonium bisulfite solution. Bisulfite was omitted in the earlier procedure. Procedure A (Recommended). Neutralize the sample solution conTable I.
Amount of Sodium C o p n e r ~ p ~ ~wu ~t r ~ m ~~ ugneaum
Sodium Added to Sample, Mg. 0.434 4.34 43.4 4340 r N a % o f N a r N a . %ofNa. r N a %ofNa ?. N a qoofNa Method copttd. added copttd. added copttd. added ertpttd. added MgNHIPOrl 40.5 9.3 227 5.2 240 0.55 47.4 10.9 286 5.6 955 2.2 MgNH4P04-2 3.4 0.78 21 0.48 33 0.08 0.76 24 0.06 5.2 1.2 33 MgCa04 1.76 0.41 8.1 0.19 45 0.10 0.87 0.20 9.6 0.22 70 0.16 66 0.15 MgQu* 0.14 0.03 0.44 0.01 2.4 0.006 0.13 0.02 0.70 0.02 2.6 0.006 0.i 0.14 0.03 2.15' 0 . 0 5 72.0b 0.17 5.20b 0.12 54.0' 0.12 MgQuz-Hom 0.02 0.004 0.13 0.003 0.70 0.002 A 0.02 0.004 0.13 0.003 1 . 0 0.003 MgQu*-Hcm 0.02 0.004 0.09 0.002 0.21 0.0005 0 . :!1 0.000005 B All samples contain 68.59 mg. of magnesium. Precipitatea had a tendency to float and were difficult t o wash. MgNHSO,-l. Magnesium ammonium phosphate, first precipitation. MgNH4P04-2. Magnesium ammonium phosphate, second recipitation MgCsO
