The concentration of silver nitrate is not critical. When the quantity of silver nitrate was varied from 7 to 30 mmoles, the determination of 0.65 mmole of phosphorus pentoxide (93.1 mg.) was reproducible within 0.1 mg. A value of 15 mmoles of silver nitrate was selected for routine use. Results (Table 11) show that from about 2 to 200 mg. of phosphorus pentoxide can be determined within 0.1 mg. The possible interference of common substances was studied. Table I11 shows that potassium, ammonium, nitrate, and acetate ions give no significant change in results. Both sodium and sulfate ions cause slightly high results when present in large
amounts. Silicate is the only substance studied that is a serious interference. This method would not be satisfactory if arsenate, chromate, tungstate, vanadate, etc., were present. Multivalent cations would also interfere. A prior removal by some other technique, such as ion exchange, is necessary before this method can be used. Chloride, bromide, iodide, cyanide, thiocyanate, and oxalate, which form insoluble silver compounds, can be removed by a preliminary volatilization with nitric acid. The solution containing nitric acid must be heated almost t o dryness to remove these anions completely. The resulting salts must be hydrolyzed for about 4 hours in warm
nitric acid solution to remove any polyphosphate that may have formed during the volatilization and heating. When nitric acid volatilization was used in the presence of 1 mmole of these interfering anions, the determination of 0.65 mmole of phosphorus pentoxide (93.1 mg.) was reproducible within 0.3 mg. LITERATURE CITED
(1) Cannon, P., TaZanta 3, 219 (1960). (2) Firsching, F. H., ANAL. CHEM.32,
1876 (1960). RECEIVED for review December 9, 1960. Accepted March 23, 1961. Southeastern Regional Meeting, ACS, Birmingham, Ala., November 1960.
Determination of Radioantimony by Extraction into Dii s 0 b uty Ica rbino I R. W. LOWE,'S. H, PRESTWOOD, R. R. RICKARD, and E. 1. WYATT Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn. A simple liquid-liquid extraction procedure has been developed for determining radioantimony in mixed fission products. Antimony(V) is extracted from a 7M HCI-6M t i 3 P 0 4 aqueous solution into diisobutylcarbinol-n-heptane ( 1 to 1 ). For quantitative measurement, the Sb(V) is stripped from the organic phase into 1 M NaOH and counted on a gamma scintillation spectrometer. At least 9570 of the Sb is recovered; no carrier is required. The procedure is rapid (30 minutes) and is also suitable for remotely controlled analyses for radioantimony. The behavior of 25 radioisotopes and of U and Th is reported.
The use of diisobutylcarbinol as a n extractant for radioantimony was suggested from the work of Moore and Reynolds (8), who observed the coextraction of Sb(V) and Pa23ainto diisobutylcarbinol from an aqueous phase made strongly acid with HCl or H804. The evaluation of diisobutylcarbinol as an extractant for the isolation of
ECHNIQUES for the extraction of antimony have been reviewed by West (16) and Sandell (1.2). Coppins and Price ( d ) , Edwards and Voigt (4, and Schweitzer and Storms (14) studied isopropyl ether as a n extractant for antimony. Others have suggested the use of amyl acetate (6), tri-n-octylphosphine oxide in cyclohexane (IO), and diethylammonium diethyldithiocarbamate in chloroform (17) as extractants. Most analytical methods for radioactive antimony employ distillation and/or precipitation techniques ( I , 3, 6), in all of which an antimony carrier is required. Extraction techniques are used in only a few methods.
50-
40-
RESULTS AND DISCUSSION
1
0 HCI 0 HzS04 HsP04
90- A 80
* "03
-
1 Present address, Vanderbilt University Medical School, Nashville, Tenn.
874
ANALYTICAL CHEMISTRY
g 60n W
6
EXPERIMENTAL DETAILS
Reagents. All reagents were analytical reagent grade. Diisobutylcarbinol (2,6-dimethyl-4heptanol), diluted 1 to 1by volume with n-heptane and the resulting solution equilibrated with an aqueous solution of the same acid composition as the aqueous phase. Ceric ammonium sulfate, solid, Ce(SO4)2.2("4) 2S04.2H20. 7 M HCl-6M HsP04. Apparatus. Gamma-ray scintillation counter having a well-type sodium iodide crystal and equipped with a differential pulse-height analyzer, a scaler, and/or a recorder.
70 -
T
radioantimony is reported herein. Throughout the study, the organic phase was diisobutylcarbinol-n-heptane (1 to 1 by volume), solutions of various acids were the aqueous phases, and Sb125 was used as a tracer.
a a k-
In -i
a 3020
-
to-
CONCENTRATION OFACIO IN AQUEOUS PHASE, M
Figure 1. Effect of type and concentration of acid in aqueous phase on extractab!lity of Sb(V)126 into diisobutylcarbinol-n-heptane
It was observed that Sb(II1) is extracted to only a limited extent into diisobutylcarbinol-n-heptane, whereas Sb(V) is extracted almost quantitatively from HCl solutions of high concentrations (10M or greater), from solutions, and to some extent from H3P0h solutions. Cerium(1V) readily oxidizes Sb(II1) to Sb(V) in strong HC1 solution (11, IS). However, Ce(IV) will not oxidize Sb(1V) to Sb(V) (16); the Sb(IV) must first be reduced to Sb(II1). The reduction is done with sodium bisulfite. The results
Table I. Extractability of Some Radioisotopes from 10M HCI into Diisobutylcarbinol-n-Heptane
Aqueous phase Composition, 10M HCI Volume, 10 ml. Organic phase Composition, [( CH&CHCHZ]ZCHOH, 50% v./v. 50% C&(CHZ)&HP, v./v. Volume, 25 ml. Radioisotope Extracted, Radioisotope" % 0.2 3.0 0.1
0.1 90 98 50 Cr
/a 0.1
97
3.0 0.2
The indicated valence state was the valence state before the reduction with bisulfite and subsequent oxidation with Ce(1V); it may or may not be the final valence state.
of a study of the extractability of Sb(V) into diisobutylcarbinol-n-heptane as a function of the types and concentrations of acids in the aqueous phase are shown in Figure 1. The curves of Figure 1 indicate t h a t Sb(V) does not extract well into diisobutylcarbinol-n-heptane from aqueous solutions of "03 and not quantitatively from aqueous solutions of H3P04. Sulfuric acid in the high concentration required is not a desirable reagent; therefore aqueous HC1 solution was chosen as the most desirable medium. It was found that HKO, in low concentration (2M),does not affect the extraction of Sb(V) from HC1 solutions of high concentration (10M). The data given in Table I show the extractability of some trace elements into diisobutylcarbinol-n-heptane from l O J l HCI. Iodine, Fe(III), Kb(V), and Pa(T'), as well as Sb(V), are extracted from 10M HC1. Oxalic acid and H3POa were tried as agents for inhibiting the extraction of these elements. The presence of oxalic acid in 10M HC1 was found to inhibit the extraction of Nb(V) but not of the others. Phosphoric acid inhibited the extraction of both Kb(V) (see Table 11) and Pa(V) but not of iodine and Fe(II1). Phosphoric acid does not reduce the extractability of Sb(V) even when the concentration of HC1 is reduced somewhat. Phosphoric acid would not be required if the nature of the sample precluded the presence of Nb(V) and Pa(V). The addition of HaPO4 to l O M HC1 lowers the HCI concentration;
therefore the extractability of trace elements was studied using a n aqueous me ium of 7M HC1-6M HaPO4. The res ts of this work are summarized in the first two columns of Table 111. The data of Table I11 show also that Sb(V) can be stripped quantitatively from the organic phase into 1M NaOH. The third column of Table I11 shows the per cent of each of the tracers that was stripped into 1 M NaOH solution from the diisobutylcarbinol-n-heptane extract. The data also show that As, Fe, Hg, Mo, Po, Tc, and Zn, as well as Sb, are stripped to some extent into the 1M NaOH solution. However, if the analyst is seeking Sb125,he will usually be working with a fission product mixture that has been "cooled" for several months. I n this case, any Mog9 (the only significant radionuclide of Mo) will have decayed through Tcg9m to Tcgg, which is a pure beta emitter and will not interfere in the gamma counting of SblZ5. Polonium-210 is also likely to be found in old fission-product solutions and is extracted quantitatively in the procedure. However, Po2lCdecays -100% by alpha emission; less than 0.002% of it decays with 0.8-m.e.v. gamma emission. This energy will not interfere with the counting of Sb125if a gamma scintillation spectrometer is used. Polonium-210 has been determined by the procedure described in this paper, with the modifications that the organic phase is stripped with water instead of with 1 M NaOH and the alpha activity of Po2l0 is counted. Moore (7) has used a similar technique for determining PoZOS. It may be more difficult to determine the other radionuclides of Sb than to determine Sb125,the difficulty depending on the activity sought and the nature and history of the sample. The more important radionuclides of Sb and the energies of their predominant photons are listed in Table IV. Of these, SblZ5,SblZ6,SblZ7,Sb12e, and SblZ9are the fission products of significance, and i t would be difficult to determine them quantitatively in the presence of each other because of their complicated energy spectra. Antimony-125 can be determined after sufficient time has elapsed for the other antimony isotopes to decay to insignificant amounts. This procedure may also have applications in activation analysis; SblZ2and Sb124might be used to determine the total antimony present. The authors have also used the procedure to determine radioactive impurities present in Sblz4and Sb125product solutions. The decontamination of Sbi25 from other fission products by means of diisobutylcarbinol-n-heptane as a n extractant warrants the use of this technique as a major isolation step for the
&
Table II. Effect of H3PO! Concentration of Aqueous Phase on Extractability of Nb(V)96from 7M HCI-xM H3P04 into Diisobutylcarbinol-n-Heptane
Aqueous phase Composition, HCl, 7M H3P0,, M indicated Nb(V)95,tracer amount Volume, 10 ml. Organic phase Composition, [( CHJ)~CHCHZ]ZCHOH, 50% v./v. CHa(CHz)&Ha, 50% v./v. Volume, 25 ml. Nb(V)gS HaPo, in Aqueous Phase, Extracted, M % 9.2 0.82 4.2 1.6 2.4 < 2 .o
