378 SHORT COM;MUSIChTIONS

Determination of lanthanum in titania by activation analysis

IDuring the determination of the cross-section of the (n,p) reactions on titanium resulting in radioactive scandium isotope+, a lanthanum impurity was discovered in the irrczdiatccl sample. The content of lanthanum was determined by activation analysis.

The analysed titania satnplc was “analytical grade” ; I~O-300 mg was weighed in a small silica vessel, Tllc 1rmthanur-n standard was a solution containing 50 ~6 oE lanthanum in ZOO ,~l of 0.x N bidistillccl nitric acid, The irradiations were pcrformccl in tIlc 1311-r reactor for 2 lr at 4 * 1011 n cm-2 SC-~.

Pig. I. I<ncliocllcmicaI separation ol lnnthnnum from TiOd. (,I) ‘JOLn; (3) 4 + %c (o.gg-I .32--2.04)

-j- "Fit (OJG) + ll%b (0.5G); (2) 3 -j- "*Wn (x.37-2.75) + lazSb (ohg-x.14-x.6) -t_ ladlSb (xX39); (I) 3 -j- ““Na (1.73-2.25) -/- 4al< (1.52).

Titania was heated with a mixture of 15 ml of concentrated sulfuric acid and PO g of ammonium sulfate. After cooling, this solution was diluted with IOO ml of

A7aul. ChL’m. Acfn, 41 (1968) 375-380

SHORT CObflbfUSICATIOSS 379

water. y-Spectrometry (Fig. I, spectrum I) showed the presence of 24Na, 42IC, I%b, =QSb, ‘*AS, 4%c, 4YSc, 14oLa.

Lanthanum was coprecipitatcd with titanium by addition of 14 M ammonia solution. The precipitate was separated by centrifugation, washed with water to which a drop of ammonia solution had been added (PH > IO) and redissolved in 3 jV hydrochloric acid ( -I- a few drops of hydrogen pcroside). In this step 2’1Na, 43Ii and partly l?Sb and ‘“AS are eliminated as can be seen from Fig. I, spectrum 2.

The titanium matrix can be separated from the rare carttls by cation cxchangc. It is c&orbed by 3 M hydrochloric acicl while the rare earths remain on tlic column, but tailing occurs. The separation can be spccdcd up considerably by means of the titanium-peroxide complex. In 0.5 N hydrochloric acid + 2% hydrogen peroxide this complex is strongly adsorbed but in 3 N hydrochloric acid + 2% hydrogen peroxide it has a distribution coefficient of less than I: and leaves tlie column without tailing.

The separation from the matrix was achieved by diluting the solution to 0.5 M hyclrr~chloric acid and adding hydrogen peroxide till the colour intensity stayed con- stant. The titanium complex was first sorbed in a narrow band on a Dowex ~oMr-~X8 loo-ZOO mesh column (20 cm x z cinz) and tllcn elutcd wit11 3 N hydrochloric acid + 2r/, Iiyclrogen peroxide. ‘I’lrc rare cart11 group was elutcd with 6 N hydrochloric acid. Tile cluate was evaporated and taken up again in 0.x ,!V hydrochloric acid. In this step, besides ttlc titanium matrix, the following isotopes were eliminated: GlCr, 182Ir, the rest of the ‘(1 As, ZdNa and IONIC. activities and part of the lY5b (Fig. I, spectrum 3).

The 0.1: N hydrochloric acid solution was adsorbed on the top of a Dowcx SOW-S8 200-400 mesh column (x5 cm x 0.4 cn+) and subsequently eluted with am- monium cc-hydroxyisobutyrate solution. In a first cxpcriment, an clution was perform- ed with a linear Iigand concentration gradient, under conditions where the rare cart11 activities should be separated well enough to allow identification of the individual elements, Four clution peaks were obtained: the first left the column during the 0.x M hydrochloric acid adsorption stage and was due to 12%b, and another left imrnedi- atcly after starting the gradient ( 182Ta) ; the two other peaks were ‘YSc + 4%~ + 4%~ forrncd by (n,p) reactionson titanium, and 14OLa. Since no other rare earths were dctect- ed, Sb, Ta and SC were separated from lanthanum as a group by elution with a ligand concentration of 0.1 M, lanthanum being eluted with 0.4 M l&and concentration. Some experiments were performed with added rb3Gd as a chemical yield monitor for the whole separation procedure. In this case, Sb, Ta and SC were eluted with 0.06 M

ligand concentration, Gd with o.12 M and La with 0.4 M. A pure I4oLa-spectrum was obtained (Fig. I, 4). In each case the different fractions were collected in standard flasks (50 ml) and measured with a NaI (Tl) crystal coupled to a qoo-channel analyser. The lanthanum standard was measured in the same geometry.

Xes1rlts and diSClf ssion Two series of determinations were performed, one with lbaC;d yield monitor and

one without. The results are summarisecl in Table I, It appears that yield monitoring is not necessary, a reproducible yield of g8-

ICOO~/~ being obtained. From these data one concludes that the sample contained 12.5 p*p.m. &0.x5 La.

AwaZ. Chiwr. Ada, 41 (rgG8) 378-380

SHORT COMMUNICATIO?JS

.._ _.-_ .A-- _.._ __ .-. __------__.-- -- a._... _ ._ ---------

IViLlr yield Jtlnlrilr,v IVillrorfl yirtd rrroniioY __.+._. _-*--_<_. - -. - _... -__-...__.+ . . _ ..-__.. _. I - _ _ .-_. ---_---- -

13.0 12.3 I’L.3 I_ 7 12.0 I z:,,

‘I‘~Ic cross-section for (n,y) cqAurc of titanium is $3 barn. From tllis value it can

(.lCcccivecl October zgth, 1937)

Some preliminary studies of the analytical potentialities of the atomic-hydrogen plasma torch

A Inajor prablcm in atomic absorption spectroscopy is the conversion of the SWII~IC solution or the solid material into atoms. For many easily oxidised elements this isoftcn difficult, even \vitll tile hottest reducing flames normally available, because of tllc presence of some atomic oxygen. More recently, tile use of the nitrous oxide- ncctylcncl flame has overcome some of these problems, cllthough its application is as yet COilfitIecl to solutions rather than solid samples and even then many elements are beyond its rcacl~, e.g. ceriuIII, thorium, etc. ; moreover, such flames usually exhibit a very high background radiation, and whilst this may be partly overcome by modulating the source lknd detector, the radiation from tile flame can still cause serious photo- multiplier fatigue,

I’lasn~as appear to offer several advantages, hence their use as atom-reservoirs in amLlytica1 spectroscopy is of considerable interest, T11ey cczn be divided into two distinct classes; the d,c. arc plasma jet and high-frecluency coupled plasmas. The former have been used in emission spectroscopic stuciies wit11 some success ilttev &a by GHEBX FIX~IJ, JONES ANIII l3~mz~z who found that tlley were somewhat unstable and produced lligh background radiation. More recently Wmn AND WILDY'~ mmaged

to overcome some of these problems by using an integrating spectrophotometer employing an additional pllotomultiplier and screening the stabiliser electrode.

Aaal. Ghir,z. Actn, 41 (1968) 380-384