Table I.
Reproducibility of Analysis of 56 p . p m Nitrogen in Argon Sample volume 2 liters
Peak area, sq. mm.
Deviation from mean value, %
735.0 702.5 686.0 '741.0 721.5 694. 8 716.9
$3.0 -1.6 -3.9 $3.8 +1.1 -2.7 $0.4 $1.6 -2.4 +0.9
725,O 696.4 720.0
p.p,m. A relative standard deviation of ~ + 2 . 3 4 7of~ the average has been calculated, corresponding to a confidence limit of 5.75% for the significance level 57,. Table TI contains data from argon containing 9 p.p.m. of nitrogen. The relative standard deviation is +5.7y0 corresponding to a confidence limit of 12.1%.
Table II. Reproducibility of Analysis of 9 p.p.rn. Nitrogen in Argon Sample volume 2 liters
DISCUSSION
done to obtain a stable base line before the nitrogen peak was recorded. S 2 retention time is 3.7 minutes. RESULTS
The apparatus was calibrated with argon containing known concentrations of nitrogen, from 3 to 350 p.p.m. Figure 1 shows a chromatogram of argon containing 56 p.p.m. of nitrogen. Under the conditions of analysis described, 1 11.p.m. of nitrogen corresponds to 6.4 Sq. mm. of the peak area. Table I shows the reproducibility of the data using a nitrogen concentration of 56
Since it is of importance that all nitrogen should be condensed, a special study had to be made to ascertain that this had been achieved. The peak areas were recorded as a function of the sample quantity. For lower and higher concentrations, straight lines were obtained which changed direction at certain points, depending upon the nitrogen concentration, and the peak area mas no longer proportional to the sample quantity. These points were considered to be breakthrough points. (See Figure 2.) ACKNOWLEDGMENT
The author expresses her thanks to Sten Mogensen, Svenska AB Gasac-
Peak area, sq. mm.
Deviation from mean value, %
112.8 111.3 129.8 130.5 116.0 114.0 130.0 123.9 126.0 115.0 129.2 123.5 126.3 116.4 115.5 118.8
-6.9 -8.2 $7.1 +6.7 -4.3 -5.9
+7.3
472.2 +4.0 -5.1 $6.6 +1.9 f4.2 -4.0 -4.7 -2.0
cumulator, Lidingo, Sweden, for having made this work possible. LITERATURE CITED
(1) Brenner, S . , Ettre, L., ANAL. CHEM. 31, 1815 (1959).
BRITT-IIARIE KARLSSON Chemical Laboratories Svenska AB Gasaccumulator Lidingo, Sweden
Determination of Americium-243 in Curium-244 SIR: The technique of isotopic dilution-mass spectrometry was applied succesqfully to the I1reci.e determination of Am243 in the presence of an approuimately equal quantity of Cm244. This method eliminates a difficult and tedious separation of americium from curium ( 3 ) . I n the irradiation of Pu23gfor the ultimate production of Cf252,irradiated target elements must be chemically processed when the fissile Pu239and P 1 1 2 4 1 are substantially depleted. At this stage, a typical target element contains a mixture of actinides of the following approximate weight per cent:
~
~
2
4
i
0
71 c o
J .heas 17 O r c C I 0 ~4c& ~ C111"4 11 0';
~
ANALYTICAL CHEMISTRY
h 2 41
~
The deterniination of all of these nuclides except .1m*43 was made by chemically separating plutonium from the higher actinides and applying established techniques (alpha counting, alpha pulse analysis, and mass spectrometric isotopic analysis). Since the specific activities of Cm242and CmP44
1312
ionization efficiency of americium was about 50 times that of curium. The mass spectrometer was a triple-filament, surface emission instrument (Consolidated Electrodynamics Corp. Model 21-702). The detection system was modified by adding an electron multiplier. Curium-243, therefore, mould not cause errors greater than 1% in the determination of americium-243 unless present in Cm243/hm243 ratio greater than 1 to 2. Since the conditions of irradiation produced a high ratio of Cm2"
1
Pr12'8
pu"1 Pu941 Pu942
are 1000 times that of Am243,Am243 cannot be determined in the presence of Cm*4*--244by alpha pulse analysis or by alpha-gamma coincidence counting. The chemical separation of americium from curium with quantitative recovery of americium is difficult and tedious (3). Beadle, et al. ( 2 ) determined Am243 in a solution that was free of curium by an isotopic dilution technique with the mass spectrometer. We analyzed known mixtures of Am241and CmZ4'by mass spectrometer and found that the
16 h *~~239-~p,240
~400
a270
ay740
Figure 1.
a,*lC?O
Formation and decay of Pu, Am, and Crn nuclides
to Cm242,Figure 1 shows that the ratio of Ah243 to Cm243must also be high, Hence, the Am243would be the only significant peak a t m:iss-243; therefore, the i9otoliic dilution technique could be applied to our mixture of curium and americiuni without chemical separation. PROCEDURE
-\ known quantity of isotopicallypure was added to an HCl solution in which a sample of irradiated plutonium-aluminum was dissolved. The solution was made 14M in lithium chloride and about C.1Jf in HC1 and was equilibrated with a 2/1 liquid ratio of 3Oy0 Alamine-336 (a tertiary amine nianufactured by General Mills) in diethyl benzene to remove the actinides from lanthanides, other fission products, and aluminum ( 1 ) . Americium and curium were then uartitioned from plutonium by s t r i p , h g into 4.851 HCI. Recovery of americium was about
75%. Approximately 957, of the beta activity, 90 to 99% of the gamma activity, and more than 99.97, of the plutonium were removed. The sample was then evaporated to dryness and redissolved in 1X HXOa, and the mass ratio of to Am243mas determined with a surface emission mass spectrometer. Correction was made for the small amount of present in the sample by purifying and analyzing an unspiked sample by the same method that was used for the spiked samples. One tenth of a microgram of americium was sufficient for the mass spectrometric analysis. h relative standard deviation of = k l . O ~ , was obtained for the analysis (including all purification steps) of seven aliquots of a single >ample. ACKNOWLEDGMENT
The authors acknowledge the work of
W. B. Hess and B. L. Bussey of the
Savannah River Plant who performed the mass spectrometric analysis. LITERATURE CITED
(1) Baybarz, R. D., JTeaver, B., Oak Ridge
Sational Laboratory, Oak Ridge, Tenn., Atomic Energy Conmi. R e p t . ORNL-3185 (1961). (21 Beadle. A. B.. Dance. D. F.. (;lover. K. M., 'Milstead, J., J . Inotg. AV~icl. Chem. 12,359-61 (1960). ( 3 ) Penneman, R. A . , Keenan, T. I0>..41.DSOS
Savannah River Laboratory E. I. du Pont, de Semours and Co. Aiken, S. C. The information cont,ained in this paper was developed during the course of wnrk under contract AT(07-2)-1 with the t-.P. ht,oniic Energy Commission.
Application of Constant Current Potentiometry to Titration of Cobalt with Potassium Ferricyanide SIR. In spite of th: small potential change a t the equivElence point, the volumetric determination of cobalt by oxidation with ferricyanide in ammoniacal solution (2) is>frequently used. This ia primarily becauqe, of the metals commonly present with cobalt in alloys and steels, only mang,anese and, to a le-er extent, chromium interfere. By application of constant current potentiometric end point detection (1, 3, d ) , ferricyanide titrations of cobalt can be performed under the original condition. with a greatly improved break at the end point. This makes plotting titration cur ;es unnecessary. The potential change a t the equivalence point is about 0.5 x olt, some three times greater than when using a conventional platinum-$ .C.E. electrode y t em. EXPERIMENTAL
Apparatus. Potential measurements were made with either a Beckm a n Model H-2 p H meter or with a Leeds & S o r t h r u p Model 7401 p H indicator. T h e electrodes were 0.016in. diameter platinum wire sealed into
soft glass tubing so t h a t about 1 mi. of wire was exposed. T h e polarizing current mas obtained from two 45-volt batteries in series with a 25-megohm resistor. A Sargent Model XV polarogrnph with a rotating platinum electrode was used t o obtain t h e current-voltage curves. Standard Solutions. Solutions of cobalt(I1) sulfate were prepared from reagent grade cobalt sulfate hexahydrate, and mere standardized b y evaporation of 10.00-nil. portions to dryness in porcelain crucibles and ignition a t 500" C. in a muffle furnace. Standard solutions of potassium ferricyanide were prepared by dissolving weighed portions of the recrystallized salt in deionized mater and diluting t o volume in a volumetric flask. These were stored in brown bottles to minimize light decompocition. Comparison of Titration Curves. Titration of 5.00 nil. of 0.1092X cobalt sulfate in approximately 30 ml. of 4;M ammonium hydroxide-1 .M ammonium citrate with 0 . 1 O O O M poTable II.
Table I. Determination of Cobalt and Manganese by Addition of Excess Potassium Ferricyanide and Back-Titration with Cobalt Sulfate - _ _ 11eq. _ taken ~
Co 0.2627
>In
Total-
0.262'7 0.3948 0.39413 0.2627 0.0247 0.2874
?vleq. found, total Ptd. dev. 0.2626 (av. of 8 titns.) f 0 . 0 4 0.3949 (av. of 4 titns.) ~ k 0 . 2 7 0.2868 (av. of 5 titns.) & O . 11
taqsium ferricyanide was performed using two sets of electrodes-a coiiimercial platinum-S.C.E. pair and a polarized platinum pair. Curves are shown in Figure 1. Values for the polarized electrodes are not given with reference t o the saturated calomel, but indicate only potential difference. The shape of a plot of potential us. ferricyanide volume using polarized electrodes may be interpreted by reference to Figure 2. which shows polarograms of solutiona similar to thohe preent before and after the equivalence point in the absence of cobalt. -4fter ferricyanide is added, but before the equivalence point is reached, the potential is governed by oxidation of ferrocyanide a t one electrode and reduction of diqsolved oxygen a t the other (qolid line, Figure 2 ) . If a polarizing rurrent of 1.8 pa. is used, the potential difference between the titration indicator electrodes correqponds to the inter5ection of this plot with the 1.8-pa. value, on the graph. At the equivalence point when a small amount of ferricyanide i present in the yolution. the electrode
Determination of Cobalt Plus Manganese in NBS Standard Samples
Meq. taken, Co plus Mn
52 c o
found,b
31eq. found, av. of Co plus Mn 6 titns. Std. dev 0.4454 0 4452 13 95 f O 07 SBS 168 0 4412 0 4445 41.S5 f 0 10 a NBS Sample 349: 13.957, Co, 0.43'5 Mn, 19.50:; Cr. SBS Sample 168: 41.205% Co, 1.50% l l n , 20.33C; Cr. Correction made for manganese oxidat'ion using S B S values.
Sample" TBS 349
VOL. 35,
NO. 9 , AUGUST 1963
1313
