0.68 f 0.02 cm. in a 0.250-inch (0.635em.) o.d. captive liquid cell. From the evaluation of spectral data obtained from solutions of praseodymium fluoride in the molten eutectic LiF-SaF-KF (46.5:11.5:42.0 mole 70) a t 540" C. in either platinum foil or copper captive liquid cells, a relative standard deviation of 2% was found for the absorbance of the praseodymium peak a t 444 mk. These data were obtained from .replicate measurements of the spectra of three samples each in the copper and platinum cells. algain the net absorbance of the solution was found by subtracting the absorbance of the solvent under the desired peak. Based on the average absorbance obtained with t,he molten salt solution arid the molar absorptivity for praseodymium in LiF-SaF-KF that ha> been reported ( b ) , the path length of molten LiF-SaF-KF, a t 540" C., was calculated'to be 0.77 cm. with a standard dei-iation of *0.02 em. in a 0 250-inch 0.d. calltiye liquid cell. The overall accuracy of the path length for this fluoride melt is not within this limit, however, because of the poorer precision associated with the molar absorptivity value ( 5 ) used in this calculation. In bot'h the aqueous and molten >alt case, the weight of the sample held in the cell mas not considered in calculating the respective path lengths.
I n evaluating the path length, or rather the absorbance reproducibility, of the molten fluoride salt solution, it became apparent that captive liquid cells made from platinum foil were not as mechanically stable as might be desired. Several experiments with these cells yielded lower absorbance values and less reproducible data, coefficient of variation of the order of 6%; the cause of this problem was traced to somewhat distorted shapes in the cell which evidently were caused by the sample filling operation. S o such problems were encountered with the copper cells, which had a greater wall thickness. Ai more stable platinum captive liquid cell should result from the use of platinum rod in the fabrication of the cell so that the wall thickness would be of the order of 0.030 inch as shown in Figure 1. Applications. The captive liquid cell has been applied to spectrophotometric studies of molten fluoride salts. It:: utility in this respect has been adequatt,ly tlcmonstrated over a period of six months. The cells should be useful for the study of other tems such as molten hydroxidcs. Captivc liquid cells should also be ideally suited to visual or spectral observation of liquid systems a t very high temperatures, > 1000° C., since this is a windowles. container and is not subject to problems of window
compatibility or black body emission from window materials. The reproducibility of path length for aqueous solutions described in the previous section suggests that these cells should be applicable to special problems in spectral studies a t ordinary temperatures, such as spectrophotometric investigations in hydrofluoric acid solutions. It has been experimentally demonstrated that captive liquid cells can be filled by pouring liquid into the cell. These cells therefore could be applied to in-line spectrophotometric analyses of corrosive liquid systems. With the advent of high intensity monochromatic light sources, such as lasers, it would seem that the captive liquid cell would be useful in Raman spectrometry of corrosive liquids and molten salts. The cell design permits irradiation of a sample through the top, whereas secondary effects can be observed through the spectral apertures. LITERATURE CITED
(1) Bues, W., 2. Anorg. Allgem. Chem. 279, 104 (1955). ( 2 ) Greenberg, J., Hallgren, L. J., Rev. Sci. Instr. 31, 444 (1960). ( 3 ) Lux, H., Siedermaier, T., Z. Anorg. dllgem. Chem. 285, 246 (1956). (4) Young, J. P., White, J. C., ANAL. CHEM.31, 1892 (1959). (5) I b i d . , 32, 1658 (1960). RECEIVEDfor review July 29, 1963. Accepted October 17, 1963.
Carrier Tech niq ue for Quantitative Electrodeposition of Actinides M. Y. DONNAN and E. K. DUKES Savannah River laboratory, E.
I. du Pont de Nemours & Co., Aiken, S. C.
b A carrier method was developed for the rapid quantitative electrodeposition of actinides from aqueous solutions onto alpha counting plates. Incremental addition of natural uranium as the carrier for actinides of high specific activity was necessary for quantitative electrodeposition. A recovery of 99.8% was obtained in detailed study with plutonium solutions, and in scouting experiments the carrier technique markedly improved the electrodeposition yields of neptunium, americium, and curium. The excellent quality of the deposits permitted alpha counting with a relative standard deviation of 2~0.2%.
.A
problem in the precise alpha counting of actinides is the quality of sample mounts. S o single rapid method of preparing samples for alpha MAJOR
392
ANALYTICAL CHEMISTRY
counting provides sample mounts that are both uniform and quantitative. Evaporation of pipetted aliquots is quantitative, but the mounts are not suitable for alpha pulse height analysis (.lPH-i) because of nonuniformity in the distribution of solids on the surface of the mount,. Sublimation gives uniform deposits, but recoveries are not quantitative and fractionation of the actinides can occur. Electrodeposition results in uniform mounts, but, heretofore, quantitative deposition methods have required long periods of time (1, 2. 4 ) . Recently, IIitchell described a n electrodeposition met,hod that is rapid and provides high yields for tracer concentrations of the actinides ( 3 ) . His interest was in analysis of the pico- to nanogram range, and he was not concerned with highly precise determinations.
R e deduced from Mitchell's data that the rate of deposition was a function of the chemical concentration of the actinide being deposited. This deduction led to consideration of a carrier technique. Rulfs and his cotvorkers showed that nat'ural uranium as a carrier increased the recovery of L?, but they did not obtain quantitative recovery (94 f 3%) (6). Our own preliminary experiments showed that uranium carrier increased the recovery of other actinides and that incremental addition of uranium carrier was the key to quantitative electrodeposition of actinides. Yatural uranium is highly suitable as a carrier becacse of its low specific activity (1.5 d./m./Wg.) and its chemical identity as an actinide. The objective of this study was to determine if IIitchell's procedure could be combined with incremental addition of uranium carrier to give quantitative
reproducible electrodeposition of microgram quantities of the actinides. EXPERIMENTAL 35
.Winides were elect,rodepositcd in a n xpparatus similar t o t h a t dcicribcd by Mitchell (Figure 1). 'Thc primary d6ference was t h e F I Z C and type of cathode. Briefly, thc apparatus included a source of direct current, a n anode stirrer, and a crll. T h e anode stirrer was made of platinum gauze a r ' d was cylindric2tl (1.8 cm. in diametw). I n addit,ion to it> other functions. the gauze tly reducctd spattering due The cell consisted of a el base with a raised circular portion to accommodate the cat'hode and a section of borosilicate glass tubing to contain the electrolyte. T o prevent leaking, a vinyl gasket was placed between the glass tube and top of the cathode. The cathode was a Haynes Stellite Co. Hastelloy 13 planchet polished to a 4-microinch mirror finish (3.65 em. in diametei,, 0.05 em. thick) with a deposition area of 5.7 sq. em. Hastelloy 13 is a nickel-molybdenumiron alloy that is highly resistant to hydrochloric acid. Springs were used to kecy the glass tubing pressed against the planchet to preT-ent leaking and control the size of the plating surface. Electrodeposited mounts were counted with a Tracerlab Automatic SC-5013 2 K windowleiss flow counter. Reagents. A standard plutonium239 solution was prepared by dissolving plutonium oxide and determining t h e alpha disintegrxtion rate from isotopic, coulometric, and alpha pulse height data. T h e purity of all other radioactive solutions was verified from alpha pulse heighl, and isotopic analyses. T h e uranium carrier was prepared from natural uranium nitrate and all other reagenk were prepared from reagent grade cl-emicals. Recommended Procedure. An aliquot of sample is added to t h e cell t h a t contains 4 ml. of a saturated solution of ammonium chloride. Methyl red is used as a n indicator. Concentrated ammonium hydroxide is added if the solution is acidic; then 1M HCl is added to adjust to p H 1. S o other pII adjustment is necessary during the electrodeposition. T h e anode siirrer is placed in the solution about ,5 mm. above the cathode. Voltage is regulated to give a current of 2 amprres throughout t'hc 20-minute depo,iition, and the anode stirrer is rotated a t 100 r.p.m. L-ranium-238 is added in three increments of 10 fig. each: one addition a t the start of electrolysi5, followed by two addition> a t 5-minute intervals. Cell and stirrer surfaces ab0i.e the liquid level are rva.5hed down witk about 4 ml. of ammonium chloride approximately half,way through the deposition. Jmmediately hefore the current is discontinued, 1 ml. of concentrated ammonium hydroxidis added to prevent the hydrated oxide from dissolving. After the current is turned off, the cell is drained and rinsed with water. The
mm
bows I
cote
glass tubing
Apparatus.
Hostelloy Plate
1
-7
Stmu
--
"5"
Vinyl Gasket toinless Steel B a r e ~~
Note Drowing does no1 show plastic top flange which I S bolted I O bare to prevent leoklng
Figure 1.
Electrodeposition apparatus
plate ib removed from the cell, r i n d with ethyl alcohol, flamed to a dull red. and counted. RESULTS A N D DISCUSSION
The apparatus and procedure, were evaluated first without uranium carrier by electrodepositing Pu23g. For 10 plates an average of 97.676 of the plutonium was deposited with a relative standard deviation of 10.76%. One addition of VZ3*carrier increased significantly the rate of deposition of Pu239. Plutonium - 239 was deposited alone and with added L723Y, and recoveries were compared a t the end of a 5minute deposition. Only 85% of the plutonium was deposited without uranium carrier. For the same length of time 93% of the plutonium was deposited Ivhen 5 pa. of carrier was added and 96% of the plutonium was deposited with 10 pg. of carrier waa used. The optimum procedure for obtaining quantitative recovery and high precision a t short deposition times was to add uranium carrier in increments. Preliminary &dies showed that electrodeposition was rapid initiallyj with or without carrier, but the rate of deposition decreased as the concentration of carrier and lor actinide decreased. Therefore, it was possible to take full advantage of the concentration effect to increase the deposition rate by adding carrier in several increments. Twenty plate? were prepared to compare incremental addition of carrier with single addition. Each plate waR prepared from a 1000-11. aliquot (0.3 pg.) of I ' U * ~solution ~ of known concentration. The same 1000-pl. Iiipet was used throughout the study, and it was calibrated to 1 0 . 6 pl. For 10 plates, 30 pg. of Y738 carrier was added in a single addit,ion a t the beginning of electrodeposition. For the other 10 plates. \yap added in three increments as described in the recommended procedure. Each plate contained about 25,000 count>$'minute and was counted for 10 minutes. One addition of carrier gave an average recovery of 98.300
with a relative standard deviation (Jf +0.7i%. Incremmtal additiorl of carrier gave an average recovery of 99.8y0 with a relative standard deviation of +O.27,. Reduction of the counting error s h o w d that' the limiting error in the recommended procedure \vab due t o pipetting and variation in electrodeposition recovcry. Each of the 10 plates prepared by the recommerlded procedure (incremcntal additioii of carrier) )vas countod to a total of 1.26 X 10' counti. This reduced the counting error to 0.03%; however, the relative standard tkviatio~i waz essentially t'lie same a,- that obtainrd by counting t o only 2.5 X lo5 counts (10minute count). The high count rate wab obtained with the automatic windowless flow count'er. Rebults 01)tained for increnwntal addition of carrier are presented in Tablc I. Counts are reported in Table 1 although complete tlisintegraticm data \vere availablc, because t h r specific activities are not known to t h r degree of precision of the total counts. Kecovc,r>was based on the plutoniunl deliosited on the plate and the plutonium remaining in the electrolyte after deposition was ConiIJleted. I'lutoniuni that r r m a i n d in th(, clcctrolytc, after deposition was detrmiincd by rcdepositing the solution aftrlr adding a known amount of L7Z33. l'he total al1)ha activity on these plates rva? detczrmineti on a proportional counter, arid the yield was measured by alpha pulsr analysis. These data were w e d to calculate the ~)lutoiiiuni losse\. ?in average of 5.5 c.11.m. wa; found in the electrolytes after dcyosition in which the total plutonium counts dr:po+itctl were about 25,000. I t was assumed that the same percent'agc of uranium and plutonium was deposited. and since the uranium \vas depoqited a t only 6 pg. c m 2 , no sclfabsorption correction was riect..-sary. This Fvab verified by calculating the, self-absorption ( 5 ) and by counting deposit.: with uranium up to 33 pg cni.2 without detecting abborption. So
Table I.
Electrodeposition of
Pu239
Count rate, c.p.m. 23331 2.5282 25309 25317 2,5359 252S3 2536;7 2523h 2,525; 2,5368
Av. 25300
Relative standard deviation 1 0 17'
VOL. 36, NO. 2, FEBRUARY 1964
393
correction was made for the alpha actii ity contributed by the L?38 since it was negligible (23 c 1i.m.). However, a correction should be made when lower levels of actkit\-’ areleposited. The carrier technique was effective in improving the electrodeposition yield of CmZd4(2 X f i g . ) > Am241(7 x 1 0 - ~ p g . ) , P3(1 pg.), and S p Z 3 7 (19 pg.). K n o m amounts of these actinides were deposited with and without addition of uranium carrier. Results in Table I1 show that, with a deposition time of 7l!2 minutes and only 10 pg. of uranium carrier, yields were sufficiently high to indicate that, quantitative deposition can be accomplished by the recommended procedure. The chemical concentrations of KpZ3’ and U 2 3 3 were relatively high, and the addition of carrier had only a small eftect on the recovery rate. This small effect is consisbent with earlier observations on the effect of chemical concentration-;.e., higher concentration causes more rapid electrodeposition. Smear tests demonstrated that when deposited actinides were flamed they adhered as strongly to t,he counting plat’es as flamed evaporated mount’s. Ten mounts were prepared by depositing Pu239(IO5 d.p.m.). Each plate was rubbed with a filter paper inches in diameter) and the papers were
counted for alpha activity. The test was repeated with fllter paper moistened with acetone. The average amount of activity removed was only 0.057, for dry smears and 0.047, for wet smears.
Table II. Effect of Carrier on Electrodeposition of Other Actinides
Recovery (To) No carrier 10 wg. UZ3*
Actinide
92 INTERFERENCES
Xitrate and sulfate in quantities above 50 mg. reduce the yield. Howexer, large quantities of salts (11-11 LiC1) can be tolerated without adverse effect on deposition. Iron or aluminum (10 to 20 pg.) drastically decrease yields. Apparently, their inyoluble hydroxides are formed in the basic region near the cathode to inhibit deposition of the actinides. Any other metals that codeposit with the actinides interfere R ith counting because of absorption. APPLICATIONS
Quantitative electrodeposition should have numerous applications in radiochemical analj 4s. The technique, coupled with alpha counting, provides a method that competes in precision with coulometric and volumetric techniques for analysis of actinides of known specific activity. Furthermore, improL ement in quantitative deposition should permit better measurement of specific activity and half life of various actinides. The simplicity of the pro-
98
94 99
98
cedure should make electrodeposition and alpha counting comparabIe to other techniques for accountability applications when the isotopic composition of the actinide is known. LITERATURE CITED
(1) Khlebnikov, G. I., Dergunov, E. P.,
Soviet J . At. Energy (English Transl.)
4, 494 (1958).
(2) KO, R., Svcleonics 15, 7 2 (1957). (3) Mitchell, R. F., ASAL. CHEW 32, 326 (1960). (4)Moore, F. L., Smith, G. m-., Sucleonics 13, 66 (1955). ( 5 ) Price, R. J., “Xuclear Radiation Detection,” p. 157, McGraw-Hill, S e w York, 1958. ( 6 ) Rulfs, C. L., De, A. K., Elving, P. J., J . Electrochem. SOC.104, 80 (1957). RECEIVEDfor review July 29, 1963. Accepted Xovember 4, 1963. The information rontained in this article wa8 developed during the course of work under rontrect AT(07-2)-1 with the C. S. Atomic Energy Commission.
Combustion Separation of Phosphorus in the Microdetermination of Sulfur JOHN M. CORLISS and ERNA J. W. RHODES Chemical Research Division, Army Chemical Center, Md.
b Because wet separation of interfering phosphate i s an additional step before the volumetric microdetermination of sulfate, separation was sought in the combustion step. Such a possibility exists with the Pregl catalytic combustion method; however, metal oxides presently recommended for phosphate retention in other combustion separations were not convenient. The properties of zinc salts recommended zinc oxide for this purpose. This material properly placed in the combustion tube retains the phosphorus oxides during the combustion while sulfur trioxide i s quantitatively collected elsewhere. Quantitative separation i s demonstrated b y the results of microanalyses for sulfur on pure phosphorus compounds and mixtures containing the elements to be separated; b y qualitative tests on combustion apparatus components after the com394
ANALYTICAL CHEMISTRY
bustion separation; and b y blank determinations and sulfur microdeterminations in the absence of phosphorus. With the interferences removed in a proven combustion step, method reliability i s on a level with other microanalytical methods for SUIfate. The method is compatible with the new, r a p i d microprocedures.
I
to envision a simpler decomposition method preparatory to elemental microanalysis than closed flask combustion (12, 13) of organic mat,erials. However, not all materials are amenable to this method. Multihalogenated benzene derivatives give low and erratic results; phopphorus dctrrminations arc at times low ( 1 1 ) ; and sulfate intrrfwcnces n-hose origins are found in the niatcrial under analysis can be removed only after esact’ing wet T IS DIFFICULT
chemical procedures ( I ) . Usually combustion in a stream of oxygen will overcome these difficulties and 1eai.e the ions of microanalytical interest in a state comparable with closed flask combustion. Thus the same finishes may be used. .Again, with mineralization in an oxygen stream, removal of most metal interferences are often easily effected. For these reasons, the Pregl catalytic combustion method (15) is considered a necessary adjunct to the closed flask in the modern microanalytical laboratory. .Iddition of magnesium carbonate a t a controlled pH with subsequent ionexchange removal of excess magnesium has been recommended for elimination of phosphate interference in the niicrodeterminat’ion of sulfur ( 5 ) . Gravimetrically, special conditions of barium sulfate precipitation are used to prevent coprecipitation of the phosphate (10).
