Neutron-activation analysis by standard addition and solvent extraction

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Talmta, 1968.Vol. 15.pp. 262to 266. Pe~amon Press. Printedin NorthernIrdmd

Neutron-activation analysis by standard addition and solvent extraction. Determination of traces of antimony (Received 31 May 1967. Accepted 3 August 1967) NEUTRON-ACTWATION analysis by standard addition and solvent extraction1 was found to be suitable for the determination of elements such as uranium* and thorium* which on irradiation give rise to nuclides which have no stable isotopic carriers. In the simultaneous determination of many trace elements by this technique the induced radioisotopes could be separated much more rapidly than by the usual methods.‘s6 In this communication the method is applied to the determiuation of traces of antimony. Although the degree of extraction of antimony(III) and (V) chlorides with amines is very high,@removal of all interfering ions by either scrubbing or stripping could not be reeked. Of the other possible solvents, isopropyl ether,’ hexone* and tributyl phosphate (TRP)’ could be applied in difkent procedures for the radiochemical purification of antimony.

EXPERIMENTAL Reagents Solvents. Isopropyl ether and hexone were used without further purification. TRP was puritkd by washing with 5% sodium carbonate solution and then with water. TRP was used as a 50% v/v solution in xylene. Antimony carrier solution. Antimony(V) solution (0.144M in 6M hydrochloric acid) was prepared as described beforef Tracers. 7rGa was prepared by dissolving irradiated gallium chloride in 6M hydrochloric acid. ‘OAswas prepared by dissolving irradiated specpure arsenic(111) oxide in hydrochloric acid. Other tracers were prepared as described elsewhere.*-6 Other reagents were prepared from high purity chemicals. The apparatus has been described previously.’ Preliminary studies The extractability of antimony and other ions was examined as follows. Five ml of acid of the

desired molarity were placed in a separatory-funnel and 50 ~1 of tracer solution were added. The solution was shaken with 5 ml of solvent until equilibrium was attained (4-5 mitt for isopropyl ether; 30 set for hexone or TRP). The bases were separated and various scrubbing agents tested. The activities of equal volumes (3.0 mlP of the organic and aqueous phases were then measured. The degree of extraction from the media tinally selected for separation is shown in Table I. TABLEI.-EXTRACTION

OF

l%Ib ANDOTHERisomer

wrm

VARIOUS SOLVENTS

Extraction, y. Isopropyl ether

Hexone

50% TRP in xylene

Isotope

“‘Sb(V) “‘Sb(II1) ‘@SC “OCo %n r*Ga 6gFe(III) ‘%W.-v) ‘O’Hg(II) Z&I) ‘WS

‘ORb

6M HCl

1.5M HCl

>99 3
73 tl.0 2.0 -

6M HCl 98.5 79
@lM HCl
4M HCl 4M LiCl >99 >99 94 ;: >99 >99 71 :: 1.5
1MHNO~
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It is clear from these results that in order to increase the separation yield in isopropyl ether and hexone extraction, antimony should be oxidixed to antimony(V), for example by the addition of concentrated nitric acidduring the evolution procedure or by the addition of other oxidizing agents such as bromine water or potassium bromate solution. The extraction of antimony(V) and many other ions from 6Mhydrochloric acid with hexone and from 4116hydrochloric acid-4M lithium chloride with TBP is seen to be very e5cient. At low acidities (O*lM hydrochloric acid in the case of hexone and 1M nitric acid in the case of TBP) extraction of all ions, including antimony(V), is very poor. However when the hexone or TBP solutions are stripped with an aqueous solution of the same acidity, antimony(V) is retained in the organic phase (92% in bexone and 80% in TBP) while all other ions pass into the aqueous phase. The behaviour of antimony is possibly due to the formation of certain extractable antimony species in strongly acidic solutions; such species are not formed at low acidities. The rates of formation and decomposition of these species result in roughly equal extraction and backextraction rates. Thus kinetic experiments (Table II) show that the rate constant of antimony back-extraction is so small that the amount of the element which passes into the aqueous phase does not increase even after 15 min shaking. The examina tion of longer extraction periods would be interesting, but is beyond the scope of the present work. TABLEIL-Erwaczr OF TIMBON xx~~~crro~ OF Sb(V) FROMO.lM HCl wrrrr HxxoNx Shaking time, min

y0 Sb in the aqueous phase Forward extraction

Back-extraction

O-1

HP

0.5 1 2 4

>99 >99 >PP >99 >99 >99

6.5 8.3 8.1 8.2 8-4 8.5 8.3

The ~rodu~bi~~ of separation was investigated by extracting increasing amounts (SO-250 ~1) of I**Sbtracer as described under Procedure and then measuring the radioactivity of 3-Oml of the final organic extracts. The results were found to vary by not more than a few per cent when an antimony carrier was used; the discrepancies increased in the absence of a carrier. In general, reproducibility is higher with hexone and TBP than with isopropyl ether. Yields > 60, POand 75% were obtained for isopropyl ether, hexone and TBP extraction, respectively. cell

of interfering ions

In the isopropyl ether extraction from 6M hydrochloric acid, iron and gallium can be removed from the extract by scrubbing with 1+&f hydrochloric acid, but about 25% of the antimony is also back-extracted and the reproducibility is poor unless a carrier is added. In the hexone and TBP extractions it is beat to take advantage of the kinetic effect on antimony back-extraction, and to perform the initial extraction from highly acidic medium, followed by scrubbing the solution with a less acidic solution. The yield of antimony is thereby somewhat reduced, but interfering elements are removed. Procedure Irradiation.

Duplicate samples of metallic ah.tminium taken from cans used for pile irradiation, standard rock W-l, and coin (an Egyptian piastre made from an album-magnesium alloy) were packed in thin aluminium foil and irradiated in a neutron flux of IO*-IOr* neutronacm-‘.sec-1 for 48 br in the UAR-RR-1 Research, Reactor at In&ass. After irradiation, samples were cooled for about 3 days. For an antimony standard, @2 ml of ~t~ony~ chloride solution (1.4 @ml) was evaporated to dryness in a quartx ampoule, and the ampoule was sealed off and irradiated along with the samnles. Pro&sing of samples and standard. Each metal sample (about 300 mg) was freed from any surface contamination bv brief washina in hvdrochloric acid before beine dissolved in concentrated hydrochloric acid to which had been aded few drops of wncentrate%nitric acid and 0.50 ml of antimony carrier solution. The sample solution was then evaporated nearly to dryness and then diluted to 25 ml with 6M hydrochloric acid containing potassium bromate (5 x 10-V@.

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Bach rock sample, after addition of 050 ml of antimony carrier solution, was dissolved in a platinum dish by heating repeatedly with a mixture of hydrofluoric, perchloric and nitric acids until silica was completely removed and a clear solution obtained. This solution was then evaporated nearly to dryness and diluted to 25 ml with the hydrochloric acid-potassium bromate solution. The simultaneously irradiated antimony standard was dissolved in hot 6M hydrochloric acid containing a few drops of concentrated nitric acid and @OSM_potassium bromate solution. The standard solution was diluted to 25 ml with 6M hydrochloric acrd. Subsequent dilutions were also made with 6M hydrochloric acid. Losses of antimony in the course of dissolution of the samples and due to adsorption on glass were investigated as for =Pa.* Losses were found to be less than 1y0 in the presence of an antimony carrier. Isopropyl ether extraction. Transfer 5 ml of the sample solution to a separatory-funnel and add to this solution 5 ml of isopropyl ether. Shake vigorously by hand for 4 min and separate the phases by centrifugation. Discard the aqueous layer. Transfer 5 ml of 1*5M hydrochloric acid to the funnel containing the organic phase and shake again for 4 min. Separate the phases and discard the aqueous layer. Measure the activity (A) of the organic layer with a single channel analyser. EIexone extraction. Transfer 5 ml of the sample solution to a separatory-funnel and add to this solution 5 ml of hexone. Shake for 30 set, and allow the phases to separate. Discard the aqueous fraction. Transfer 5 ml of O*lM hydrochloric acid to the funnel and shake for 30 sec. Separate the phases and discard the aqueous layer. Measure the activity (A) of the organic layer. TBP extraction. Transfer 5 ml of the,sample solution to a separatory-funnel containing 2.5 ml of 12M lithium chloride solution. Add 5 ml of 50% TBP solution in xylene, this solution having been previously equilibrated with 10 ml of 6M hydrochloric acid. Shake for 30 sec. Allow the phases to separate and did the aqueous layer. Add 15 ml of 1M nitric acid to the organic layer and shake the funnel for 30 sec. Discard the aqueous layer after phase separation. Measure the activity (A) of the organic layer. Repeat the procedure used, on three 5-ml samplealiquots spiked with 50,100 and 15Oplrespectively of antimony standard solution. Measure the activity (A,,J of the tinal organic layer from each solution. The antimony content (x) of a given sample is calculated from the relationship

where x, is the amount of standard added.’ RESULTS

AND DISCUSSION

The results of determination of antimony in samples of aluminium, rock W-l and piastre by the procedures described are presented in Table III. TABLEIII

Method Isopropyl ether extraction Hexone extraction TBP extraction

Activity,*

Sb content,

Sample

Weight of sample in aliquot, g

coimts/30 secjml

PPm

Aluminium W-l Piastret

0.1024 0.0148 0.0520

1588 3760 61,650

0.058,@063,@054 0.95, 1.2, l.o(l*lt) 465, 4.36, 5.10

W-l Piastre$

0.0148 0.0520

4824 77,045

1.05,0*78,0.96 4*4,4*5,4.6

Aluminium W-l Piastref

0.1024 0.0148 0.0520

1573 4195 67,843

0.055, 0*058,0056 0.88, @95, 1.1 4.73, 4*9,4.4

* Activity of the r’%b + **‘Sb photopeaks at O-564 and O-603MeV, respectively (channels 12-16). t Average of the previously reported value&r0 $ Standard deviations 0.6, 0.2, 0.4 ppm for the isopropyl ether, hexone, and TBP methods respectively.

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The radiochemical purity of the antimony extracts was demonstrated from the identity of the peaks of these extracts and of the simultaneously irradiated antimony standard (Fig. 1). Purity was also confirmed by the decay curves. From Fig. 1 it can be seen that the antimony separated is sullenly

I

0

I

I

0.5 ENERGV, Mel’

1.0

FIG. l.--Gamma-ray a-Isopropyl

spectra of Sb standard, and of extracts isolated from samples of W-l. ether extract; b-TBP extract; c-Hexone extract; d-Irradiated Sb Standard.

pure for the analysis to be done with simple counters. The purity of the antimony separated from W-l (a complex material containing varying proportions of almost all elements present in the periodic table) indicates the general applicability of the method. The given procedures are. more simple and rapid than the methods reported in the literature for the neutron activation analysis of antimony.ll-l* Each of the procedures described here includes only two extraction steps, whereas the other published methods include 6 or 7 purifkation steps and the chemical yield of the isolated radioantimony must be determined. The hexone and TBP procedures are to be preferred to the isopropyl ether procedure because of their rapidity and the higher volatility of isopropyl ether. Nuclear Chemistry Department Analytical Chemistry Division Atomic Enemy ~t~~~ent Cairo, U.A.R.

A. ALIAN R. SELWANA W. SANAD

National Centre of So&land Criminological Research, U.A.R.

B. ALLAM

Chemistry Department Cairo University, U.A.R.

K.

~ALIFA

Short communications

266

Summary-The application of neutron activation analysis by standard addition and solvent extraction to the determination of traces of antimony in ahuninium and roeks is reported. Three simple extraction procedures, using isopropyl ether, hexone, and tributyl phosphate, are described for the selective separation of radioantimony from interfering radionuclides. Antimony concentration is measured by counting the activities of the l*?Sb and r*%b photopeaks at 0564 and 0603 MeV. R&un&-Gn d&it l’application de l’analyse par activation de neutrons avec addition d’etalon et extraction par solvant au dosage de traces ~~~o~e dans l’~~ium et les roches. On d&it trois techniques d’extraction simples, utilisant P&her i~p~pylique, l’hexone et le tributylphosphate, pour la separation du radioantimoine des radionucleides g&rants. On meaure la concentration de I’antimoine en comptant les activites des photopics de l%b et lrdSb ii 0,564 et 0,603 MeV. Z~Die neutron~~~e~~~i~he Bestimmung von Antimouspumn in Aluminium und Gesteineu durch Zugabe eines Standards und Solventextraktion wird mitgeteilt. Es werden drei einfache Extraktionsvorsc~ten mit IsopropyUther, Hexon und Tributylphosphat zur selektiven Abtrennung von Radioantimon von stiirenden Raldionukliden beschrieben. Die Antimonkonzentration miut man durch Zghlen der Aktivit&en in den Photopeaks von ?Sb und ?ib bei 0,564 und 0,603 MeV. REFERENCES 1. A. Alian, A.E.E.T. Report-217, Atomic Energy Establishment Trombay, Bombay, India, 1965. 2. A. Alian and R. Parthasarathy, Anal. Chim. Actu, 1966,35,69. 3. A. Alian and W. Sanad, ibid., 1967,38,327. 4. A. Alian and A. Haggag, Ta&nta, 1967,14,1109. 5. A. Alian and R. Shabana, ibid., 1968,15,257. 6. A. Alian and W. Sanad, ibid., 1967,14,659. 7. N. H. Nachtrieb and J. G. Conway, J. Am. Ckem. SOL, 194&70,3547. 8. H. Got&, Y. Kakita and T. Furukawa, Nippon Kagaku Zasshi, 1958,79,1513. 9. T. Ishimori and E. Nakamura, JARRI-1047, Japan Atomic Energy Research Institute, 1963. 10. M. Fleischer and R. E. Stevens, Geochim. Cosmochim. Acta, 1965,29,1263. 11. A. A. Smales, D. Mapper, A. J. Wood and L. Salmon, Report AERE C/R 2254 Atomic Energy Research Establishment, Harwell, 1957. 12. G. W. Leddicotte, Private ~~~~tion, 1960; quoted from NAS-NS 3033, February 1961. 13. R, A. Killick and D. F. C. Morris, Talanta, 1962,9,879.

Talanm, 1968. Vol. 1s. pp. 266 to 269. Pergamon Press. Printed In Northern Ireland

~orn~a~ne

hy~o~~o~de as a new redox indicator in vanadametry

(Received 8 February 1967. Revised 4 Jut’y 1967. Accepted 26 September 1967) IN A mmm~ communication, Sanke Gowda and Shakunthala” reported the use of chlorpromazine hydrochloride (CPH) as a new redox indicator in the vanadametric titration of iron(H) and molybdenum(V), and pointed out its advantages over ~phenyl~~e, ~ph~yI~dine, diphenyl~e.&phonic acid, N-ph~y~t~~ic acid and cop~r-ph~~y~~~~as~pho~c acid, which have been proposed as internal indicators in vanadametry. A thorough study has now been made of the mechanism of the action and use of promethazine hydrochloride (PII), IO-(2dimethylamino-l-propyl)phenothiaxine hydrochloride, as a redox indicator in vanadametry. The indicator gives a colourless aqueous solution, stable for about 2 weeks and then slowly undergoing atmospheric oxidation and becoming light pink. Like CPH it undergoes one-electron