The oscillopolarographic determination of uranium and thorium in supporting electrolytes containing cupferron

Chimira Rcfa ~fScvfer Dublishinl: Company. Printed in The Ncthcrlands

A8aiylicu

Amsterdam

THE OSCJLLOPOLAROGRAPHIC THORIUM IN SUPPORTING

DETERMINATION OP URANIUM AND ELECTROLYTES CONTAINING CUPFERRON

The polarographic behaviour of cupferrun and systems formed by cupferron with various cations has been studied by several authors. Two cupferron polarographic waves have been described; the first corresponds to the reduction from the acid form to phenylhydrazine and involves 6 electrons; the second, involving the transfer of 4 electrons, corresponds to the anion reduction. The latter only occurs at pH values above 6.G r-3. Studies of systems formed by a cation and cupferron have shown the influence of chelation on the cupferron wave in acidic media, and various amperometric methods for the determination of cations have been developed 4-O. The uranyl-cupfcrron system has received special attention 10-13. RULFS AND ELVING~~ demonstrated that _$e formation of a uranium(IV)-cupferrate film on the surface of the dropping mercury prevents the uranyl ions from approaching the electrode. The oscillopolarographic behaviour of some cations in the presence of cupferron and the development of oscillopolarographic methods in supporting electrolytes containing cupferron have not previously been studied. In the.work described below, the oscillopolarographic activity of cupferron in different supporting electrolytes was examined, and sensitive methods which permit the identification and determination of some cations, especially uranium and thorium in the presence of various metals, were developed. On the basis of the polarographic studies quoted above and of the experimental observations obtained in the present work, it was possible to explain the behaviour of uranium and thorium in these supporting electrolytes. E.Xl’ERIlUGNThL

I?tstvl~mentatio?t and chemicals A Polaroscope model P 576 (Krizik, Prague) was used. S@$orti~tg electrolyte A, 0.x M perchloric acid, 0.5 M ammonium thiocyanate, 5 10-a M cupferron. Sz~~~o~~~?~~eZectroZyte 33, 0.1 M succinic-succinate buffer pn 4, 0.x M sodium chloride, zo-J M cupferron, 0.05% gelatine. The cupferron used was of p.a. quality and was obtained from: Carlo-Erba, AnalaR, Union Chimie Belge, and Math&son, Coleman and Bell. The results were the same in every case and reproducible results were obtained with solutions stored for up to 15 days protected from light. The work done in inert atmospheres (obtained by l

Anal.

Chim.

Acta,

42 (1968)

rag-1x8

II0

0.

I)oNoso

Iv.,

M. A. SANTA

ANA

V., f. CHADWICK

ti.

tlie elimination of oxygen wit11 nitrogen) gave results the same as those obtained in the presence ol air. Slnndavd soZutiom. A 10-2 M uranium(VI) solution was prepared from AnalaR solution from AnalaR thorium uranyl acetate dihydrate and a Io-? ILI thorium(IV) nitrate hcxahydrate. 1’1~ latter was standardized with BDTA. A uranium(IV) solution was prepared by reduction of tllc uranyl solution with zinc amalgam. All tllc solutions were prcparcd in twice-distilled water. In the electrolytic cell a clroppin~ mercury clcctrodc was usccl as cathode with a mercury pool anode.

The oscillopolarograpl~ic behaviour of cupfcrron was observed in several buffered solutions. At PH values lower than 3, the cupferron gave an irrevcrsiblc cathodic incision (Q ranged between 0.52 and o.G6). The highest sensitivity was obtained between PH I and 3 (Fig. I). In highly acidic solutions, the indentation was smalle:; above PH 3 the oscillopolarogram showed two or more incisions but these were less sensitive than those observed at lower PH values. ‘I’hc potential of the main inclcntation was -0.8 V at PH I ; this incision should correspond to the reduction from The incision observed at higher pi values in the the acid form to phenylhydrazine. negative potential region (Q=o.+0.9) should correspond to the anion reduction.

Fig. I, Oscillopolnrogran~

)f 3. x0-6

M cupfcrron

in 0. x AT pcrcllloric

mid.

The sensitivity of the cupferron incisions decreased greatly in the presence oE surface-active substances as gelatine and with the addition of thiocyanate, iodide and bromide, which caused a shift of the incision to more positive potential values (Q=0.56 in a supporting electrolyte consisting of I lb1 perchloric acid and o ~5 M ammonium thiocyanate). Oscitlo~olnro,nva~hic belraviozw of some cations in suj5fiorting eZectroZytes containing cufiferron Inorder to record the activity of various cations in supporting electrolytes containing cupferron, those supporting electrolytes were chosen in which the cupferron incisions were smallest or completely absent. These supporting electrolytes were denomi-

OSCILLOPOLAROGRAPHIC TABLE ACTIVITY _.._ _.._-

DETERMINATION

OF u

Th

III

I OF

.._..._ - .-..-

SOME

IONS

IN

SlJPI’ORTINC

ELECTROLYTRS

--_-

A

__._________

Q

Sorsilivity

'l-l(I)

-

-

Pb(I I) Mn(lI) Co(LI) Ni(ll) Cu(II) %n(Il)

0.25a*=

3 * 10-00

_-.._--.-_______~_-.._.__._--.._

0.410 0.73O 0.51a

x.10-0

Cd(l1) SIl(II) Cr(I1 L)

0.3(ia*o 0.33s*= 0.280

2. lo-no I.lIO-bo

Fc(II1)

-

o*!x” -

Al(LlI) Ga(II 1)

0.63'*0

2.10-60

3.10-a= -

-

I

l

10-00

0.410

1.10-o

As(

0.7ac -

-

-

-

111)

Bi(lI1)

X.10-5

La(II1)

-

-

;$!I$)

0*73O 0.8~0

%r(IV)

O.GGQ

AS(V)

IV)

Cr(V1)

Supporliu~ cle~lrolyte 13 -(AI)

0 _______________._.--__._________

S:,rsitivit.y

0.3ObO 0.33.10

I. IO-Jho

o.go"ol* 0.300 0.71"1'~

0,.10-a 4.10-a

O..+.l’*

3.10-6a

o.qon*o o.550*“’ o.boo.“’

6. x0-80 3.x0-50 2 *10-o

-

-

2.10-60

-

0.750,id

I.

0.43. 0.‘)7"

I * 10-00

0.7&w 0.45O

2.10-5

0.160

I * xo-~~

0.210

IO-a0

1.10-b

I * 10-80

-

4.10-a 5.10-4

0.780 -

4.10-T -

I.

-

-

3.1o-fh.0

o.so“*“'

-

-

-

-

o*7s"

3.10-7

o.5oW' 0.73O

4.10-a

-

-

-

-

x0-4

id

-

(&I)

2*x0-“0

-

. '0.33a*n

Sn(IV) VW)

I3 ._-.--_-----.

-

In(II1) Sb(III)

AND .__...

Srrpporfi~r~ clcclrolylc ~1 -----

fd?Z

Mo(V1) U&.t;nd

AND

1.x0-6

3.x0-7

-

= Anodic incision. 0 Cathodic incision. ‘4 111 defined.

nated as A and B (see EXPERIMENTAL). Table I shows the position of the incisions on the curve dE/dt = f (E) in Q va 1ues and the sensitivity of each incision in terms of molarity. Sz#~o~ti~zg electrolyle A. In this medium, indentations were observed for Cu(II), Cd(II), Zn(II), Pb(II), In(III), Ga(III), Ti(IV), Zr(IV), Th(IV), U(V1) and U(IV). The Cu(II), Zn(II), Pb(I1) and In(II1) incisions also developed in supporting electrolytes which were free of cupferron and therefore were caused by the reduction of the thiocyanate complexes. The incisions of Ga(III), Ti(IV), Zr(IV), Th(IV), U(IV) and U(V1) occurred only in the presence of cupferron. The incisions of Ti(IV), Zr(IV) and Th(IV) were ill-defined and showed low sensitivity. On the other hand, those of Ga(II1) (Q=o.63) and U(IV) and U(V1) (Q =0.75) were very well defined and sensitive (Fig. z a, b). Su#+wtilzg electrolyte B. In this supporting electrolyte, In(III), Th(IV), U(V1) AnaZ. Cirim. Ada,

42 (xgG8) Iog-118

Ci. DONOSO

1x2

N.,

M. A.

SANTA

ANA

V.,

I. CHADWICK

W.

U(W) presented the most sensitive indentations. In some instances, e.g. arsenic(III), the presence of cupferron inhibited the characteristic incision of arsenic(III) in weakly acidic media. The incisions of Th(IV), U(W) and U(W) only occurred in the presence of cupferron (Fig. 3 a, h, c, d) and the indiunl(II1) incision was much more sensitive in the presence of this reagent. mcl

Fig.

‘I’ro-0

2.

(a) ~scillopol~ro~r~m 111 U(W).

of supporting

clcctrolytc

A.

(b) Supporting

clcctrolytc

A with

Fig. 3. (a) Oscillopolarogram of supporting electrolyte 8. (b) Supporting electrolyte B with 4. so-a M U(V1). (c) Supporting elcctrolytc I3 with 4’ IO -0 M Th(lV). (cl) Supporting electrolyte I3 with 4.x0-0 M U(V1) and 4-10-a M Th(IV). Anal.

Cirittr. Acts, 42 (rgG8)

109-x

rS

OSCILLOPOLAROGRAPHIC

DETERMINATION

01: u

AND

‘i-11

1x3

The incision of uranium in the A and B supporting ctcctrolytcs was also observed in sever-a1 buffered media between pH o and 5 (acetic-acetate. formicOn the basis of previous studiesi@-12, the different formate, tartaric-tartrate). reactions of the cupferron with U(VI) and U(IV) and the oscillopolarographic behaviour of cupferron in different media as mentioned above, a number of conclusions were drawn. The uranium(V1) is reducccl to uranium(V) in the region of the most positive potentials. The corresponding incision appears distinctly only if the uranium(V1) disproportionates concentration is higher than IO -3 M in the cell. The uranium(V) into U(V1) and U(IV); the latter, even in highly acidic media, precipitates as urathus shifting tltc disproportionation equilibrium and fanium-tetracupferronatc, vouring the reduction of U(W) to U(IV). The cupferron is thus changed to a form which is very difficult to reduce and its incision is shifted to the most negative potential region. The incision at -1.3 V in these media is thus the cupferron incision of uranium(IV)-cupferronate. The following observations support this idea: (a) substances like EDTA which form U(W) compleses, decrease the incision; (It) ura!liu~ll(IV) behaved exactly like uraniulll(VI) (zinc(f1) was present in the U(IV) solution used, but did not interfere because of the low sensitivity of its incision) ; (c) the potential of the characteristic incision of uranium was -1.3 V, while that of cupferron was -0.8 V in an acid medium; (d) an increase in temperature had a more marked effect on the cupferron incision in acid medium than on the uranium incision. In supporting electrolyte A, an increase in temperature accelerated the decomposition process of the acid form of cupferron, which at the same time, determined the elimination of the uranium incision. In supporting electrolyte B, on the other hand, an increase in temperature had no noticeable effect on the uranium incision. Further evidence was provided by the fact that above pH 5, the incision of uranium was as ill-defined and insensitive as the cupferron incisions. Cupferron forms a complex with uranium(IV) which is stable even in highly acid media, whereas uranium(W) only forms a &elate between PN 4 and 7. The high sensitivity of the uranium incision, especially at the first curve, is due to the adsorption of the comples at the electrode surface. Gelatine and other surfactants which decrease the cupferron incision, have a smaller effect on uranium. Tlrorizcnr. The incision of thorium in supporting electrolytes A and B should correspond, as in the case of uranium, to the reduction of the Th(cupf)=+ which is adsorbed on the mercury surface. Its potential is -r.4 V. Substances such as fluoride and EDTA which form complexes with thorium(W) eliminate the indentation. An increase in temperature and the addition of gelatine have the same effect as in the case of uranium incision. It cannot be supposed that tllorium(I~) could be reduced to the metal, since this would require extremely negative potentials. The fact that uranium and thorium behave similarly reinforces the previous interpretation of the incision.

Uvasiwu.

Detection and detevwkation

of wahrm

It is possible to detect 3. IO -7 M of uranium in supporting electrolytes A and B and to determine between 6 +IO --7 and 2.10-s M of uranium in supporting electrolyte A+zal. CWinr. Acta,

42 (rgG8)

xog-xx8

G. IIONOSO N., M. A. SANTA ANA V., I. CHADWICK

rrq

W.

h

h 12.

2Ei.

1 (

2;

,

?E

14

IC 6

E 5.

2

4-i0

2 10-6hI

Pig. 4. Calibration

curve of U(V1) in supporting

clcctrolytc

A.

Fig. 5. Calibration

curve of U(VI)

clcctrolytc

13.

in supporting

4 u (VI)

6

A, and 8. IO-Wi IO --O M of uranium in supporting electrolyte B, These results were obtained by reference to calibration curves drawn by plotting &values ZIS.conccntration (12represents the distance between the extreme of the incision and the half line of the curve) (Figs. 4 and 5). As shown in Table I, of the 27 ions examined, the following have indentations near that of uranium: for supporting electrolyte A, Zn(II), As(III), Th(IV), Ti(IV) and %r(IV); for supporting electrolyte B, Zn(II), Sn(II), AsfIII), Ga(III), Th(IV). All the incisions, except that of thorium, are much less sensitive than that of uranium. Moreover, other ions affect the sensitivity of uranium although the,y neither cause incisions in the negative potential region nor deform the oscillopolaro&am. The limiting ratios for a maximum error of f 5% are shown in Table II. In supporting electrolyte A, there are fewer interferences than in supporting electrolyte B, because in medium A some cations form thiocyanate complexes which aremore stable than the corresponding &elate. Anions such as nitrate, sulfate, chloride and acetate in concentrations up to 0.x M have no influence in either of the supporting electrolyte. l

EZintisalio?t and se@zration of interferences Arsenic(III), antimony(II1) and tin(I1) can be previously oxidized with hydrogen peroxide to prevent their interference. It was not possible to eliminate other interferences by the addition of complex-forming agents. EDTA or fluoride could, however, be used to eliminate small quantities of thorium; the incision of

OS~:II,I.OI’OLhIZOGRAPHIC

TIIE

INFLUISSCIS

01’

(Limiting:

ratio

Ion

J.

c_

IONS

1 I)

Mn(l I)

10-fi iv I/( I’/)

13 1 I’)

IfI)

/O?&/U(

VI)

-

‘I’tl(Lv)

j.._-._ . IO - 0 nr T II ( / _ -__ ___._lO~l/TlI(

u

ASI>

‘t%

I>BTlZI~hllNhTlON

- __.. ._.-.._....._. -.--

-.._ .

6) Iolr ._.__. _

.#* x0-a 111 U( VI) --...---..__ - .. SIlpporf lo,r//l(

80

IO0

As(I

II)

02

58 00

20

Sb(I

I I)

“-7 50 5 25 10,

13i(l I I) I,a( I I 1) Th(LV) l’i(lV) %r(l V)

If2 I2

30

8

250 f2G.)

30 35 I0 127

320

IO

4 IO

Cr(lIl)

I 0

IO

Fc(lI1)

12s 300

0 300

Ga(lll) 5: ._ .__._..-

_

.

.5

0 . ‘2

O-3

0.3

7

3

__.

.._

-

iI 1’1)

support lota/Tlr(l

2

2

7 5

7

T/r(lV) ..____ s I’)

I I2

I:!

GIS Go

0.6

k”,

‘2 8

-

0.5 I G

Sll(lV)

IIG

‘)“-

X’(V)

40 100

IG

5

300

300

JIo(V1)

I

U(V1)

-t

\V(VI)

Cr(VI) .

Support /1m/U(

3 130 370

As(V)

50

A I.‘I/

/I* zo-uhf _..... _. --._--_-

. . . _ __..- ___. .._ _.__.___._ ^_,___.___._ _ .__.__ _.~_______

360

Cd(II) Sn(I I)

__._.

AND

strfJfio,r

ZIl(II)

lll(171)

IJ(\‘I)

OF

of o:/,)

fon/zJ(

56 250

Al(III)

TIIXX

error

. _._. ._..-___ _._-- __.. - ___. _..__ Sr6pport .A Support B

Co(I1) Ni(I1) Cu(ll)

ON

for a maximum

...__- _....__.__...__.._...___._.__.

Tl(I) I’b(

SOMI5

DETEHMISATIOS

.

_

2

-

0.2’

8

10

2

IO

10

X0

. .- . .

.

_ ._--

---_.-

--. ._.. - ___.__

thorium is more affected than that of uranium by the addition of small quantities of EDTA or fluoride. If the EDTA or fluoride concentration does not csceed 5. x0-3 M, then a uranium concentration of x0-6 M can be determined in tlic presence of IO-~ M thorium in supporting electrolyte 13, without interference and with a masimum error of less than rfr:5:/o. The separation of interfering ions is important when supporting electrolyte B is used, as shown in Table II. In this electrolyte, Fe(III), Ga(III), Th(IV), Ti(IV) and Mo(V1) interfere, when the concentration is less than g-fold that of uranium. In supporting electrolyte A, only gallium(II1) interferes (arsenic(II1) is osidized wit11 hydrogen peroxide). Most of the interfering ions can be precipitated by means’ of cupferron and extracted together with the excess of cupferron. The precipitation and extraction were done in 0.x 1M hydrochloric acid solution containing uranium and the interfering ions. Uranium(V1) is not precipitated under these conditions. A G0/Ocupferron solution was used to precipitate the cupferronates and the extraction was carried out with chloroform. After three successive extractions, aliquots of the aqueous phase were added to supporting electrolyte B to register the uranium indentation. When I mg of each of the following ions, Fe(III), Bi(III), Ga(II1). Zr(IV), Ti(IV), Mo(VI), In(III) and V(V), was estracted from a hydrochloric solution containing 23 ~6 of uranium, the uranium could be determined with a masimum error of less than & 5%. In supporting electrolyte A, the same result was obtained by separating Gn(III), Ti(IV) and Mo(V1) from 23 ,ug of uranium.

The characteristics of the methods developed llelp to solve some important problems in chemical analysis. Uranium can be determined in supporting electrolyte A without previous separation in the presence of large quantities of metals such as Pb, Bi, V, Fe, La, etc., which generally accompany it in natural samples. The determination is also possible in the presence of small quantities of thorium without preAwd.

Chim.

A&z,

42 (x968)

xog-1x8

____

G. IIOKOSQ N., M. A,. SANTA ANA V., I. CHAt’IWICK W,

rr6

vious separation. If frigh concentrations of Ga, Ti and Me are present, only a simple preliminary extraction is necessary. In order to test the methods devclopccl, carnotitc and coal from California were analysed. Thcsc samples contained rg and o.08ryh of uranium rcspcctivcly. Curltotite. 0.5 g of carnotitc was dissolved in a mixture 0f nitric and hydrofluoric acids, then the nitric acid was eliminated with sulfuric acid and the solution was cvaporatecl to dryness. The resicluc was dissolved in 25 ml of 4 M hyclrochloric acicl and the solution was diluted to 250 ml with water. A ro-ml aliquot of this solution was diluted to 100 ml, to obtain a 10 -4 M uranium solution. This solution also contained vanaclium in a ca. 1 : r molar ratio to uranium, but this did not interfere; traces of Fe, Ni, Zn and Ccl prcscnt also did net interfere, A method of comparative titration was used to determine uranium, titrating with a X0-5 M uranium(V1) standard solution, Several analyses following methods A or 13 showed an avcr:rgc crrer of f 33,. Coalfrom Calif?wwia. 0.5 g of as11 obtained after calcinntion of the sample was dissolvecl in l~yclrofluoric-sulfuric acid mixture as described above. The residue was dissolved in 4 M hydrocl~loric acid and the solution was diluted to 50 ml. To 5 ml of this solutiqn, I ml of 6% cupfcrron was added and the cupferronatcs and the excess of cupfcrron were ektracted with ct~lorofortn. The aqueous phase was cvaporated to dryness, the residue was dissolved in O,T M hyclrochloric acid and the solution was dilutecl to TO ml. Aliquots of this solutian were used for oscillopolarographic analysis by the methocl of comparative titration using supporting electrolytes A and 13. Four analyses showed an average error of 3_ s”/i,. Detectioft aml ~~ete~7q~iq~atio7~ of t~to~iz~q7~ Supporting clectrolytc B is the more suitable

for the determination

h

-6&i

Fig. 6. Cnli~xdtion Rmzl. Clht.

ctwvc of Th(IV)

rlctn, .)2 (rgt8)

rag-I

-Th(iv) in supporting electrolyte 18

33.

of thorium

OSCII~I.OPQLAI1OGl~APHLC

IIETERMLNA’I

ION

OF

u

ANID

Th

==7

because it gives a better ratio of It-value vs. concentration. With electrolyte B, the -0 M of thorium can be determined limit of detection is 4 n10-7 M and S +IO-7-G.10 (Fig. 6). The most sensitive incision near that of thorium is the uranium incision (Q =0.73). Those of gallium(III) (Q=0.75) and zinc(H) (Q=o.71) are ill-defined and rather insensitive. Some other ions decrease the sensitivity of the thorium incision. The limiting ratio for a masimum error of 5% is shown in Table II; Fe(III), GafIII), Ti(tV) and V(V) are the most important interferences. The method permits the determination oE thorium in the presence of large amounts of I’l, Pb, V, Bi, Cd, Mn, La, etc.

Uranium(V1 and IV) and thorium(IV) give cathodic indentations in supporting electrolytes prepared from 0.1 M perchloric acid, 0.5 M ammonium thiocyanate and 5. x0-3 A4 cupferron (solution A) or from 0.x M succinic-succinate buffer PH 4, 0.x M sodium chloride, x0-3 M cupferron and o.ogD/a gelatinc (solution B). The uranium indentation on the dE/dt=f(E) curve (Q=0.75 and 0.73) permits its detection at the 3. x0 -7 M level. The thorium indentation (Q= 0.78) permits its detection at the 4. IO-? M level in solution B. Methods for the elimination of interfering ions for the uranium determination arc described. In the determination of thorium, Ga(III), I?e(III), Ti(IV) and U(VI) interfere.

L’uranium(V1 et IV) et le tlloriu~n~IV) donnent une indentation cathodiquc clans une solution contcnant de l’acide perchloriquc (0.x M), du thiocyanate d’ammonium (0.5 M) et du cupferron (5 *IO -3 M), (solution A) et avec un tampon succinique (0.1 M pfi 4)‘ du clrlorure de sodium, (0.x M) du cupferron fro-3 M) et de la gelatine o.o~O/~ (solution B), L’indentation de l’uranium sur la courbe dE/dt= f(E) (Q =0.75 et 0.73 respectivement) est perceptible h partir d’une concentration de 3.x0-7 M; alors que dans la solution B l’indentation du Th (Q=a.78) peut etre percue B partir de 4. x0-7 M. Les indentations correspondent & la rdduction des complexes du cupferron des ions genants adsorb& sur la goutte de mercure. Des mCthodes d’elimination d’uranium sont egalement d&rites. La d~ternlination du thorium est spdcialement gQn@e par Ga(fII), Fe(IIi), Ti(IV) et U(V1). ZUSAUMENFASSUKG

Die oscillopolarographische Bestimmung von Uran und Thorium ist durch kathodische Anzeige mit einem Elektrolyten mijglich, der 0.1 Al Perchlors%urc, 0.5 M Amrnoniumthiocyanat und 5 IO -3 M Cupferron (Lijsung A) oder 0.1 M SuccinSuccinat-Puffer vom pw 4, 0.1 M Natriumchlorid, x0-3 M Cupferron und 0.05% Gelatine (Lasung B) enthalt. Uran kann bis 3*ro -7 M, Thorium mit der Lasung B bis 4*1o-7 M nachgewiesen werden, Es werden Methoden zur Eliminie~ng stijrender Ionen bei der Uranbestimmung beschrieben. Die Bestimmung des Thoriums wird durch Ga(III), Fe(EII), Ti(IV) und U(V1) gestijrt. l

Anal.CLinz.

Ada,

42 (1968)

rag-1x8

G. DOSOSO

118

I 1. hq.

~~OI_‘I’XIOI’Iz

2

OLSON,

E.

c.

3 I’. J.

1:tVING

I’.

G

1.

J. 31.

/\.

I:I.VJNG

12.

AND AND

KOLTJI~IW

hl3I
T/rcsis,

AND

4 Y. UsA’ruNIco 5

AND

Ph.D.

ANJ~

1’.

j.

l
J 1 c..

JO

1,.

ItIJl_lW

12

j,

I
1.‘.

%/l. AND

AND AND

i\. I’. 1:.

BIiclliynJl,

IJZ. C/lCiU.

SOC.,

70

SANTA

(II)<+8)

ANA

V.,

I. CHADWICK

W.

1885.

1955.

79 (1957) 2697. C)I.SON, ./. nt,l. ChlU. SOC., 78 (1956) 4206; 1;. I~ISKLICSJIOVA, %rrvodsh. hxb., zf (1955) 779; C./I., 53 (1959)

c.

OLSON,

11.

/fIld.

J,IJIJ:wJ,

f’hi?U., I:.

ANI> X9

c;

I
c.

OLSON,

1’. 1)

c/wtw.,

J.

.dW.

.‘~Illd.

Chlil., ~klW1. ~hc~ll.,

(IQ56)

(1949) 26

E~-V~NC;,

(JQ,Gfi).

a‘fUd. ./.

28 7.)

./l~ud.

Il’RIVlS,

J.

C/fc?,l.,

ntldysl,

7 1.;. C. OLSON AND 1'. J. ELVJNG, 8 G. 1). S. SA~AIXIA, CII. I
Cj 1<. ‘I<. SIJAI
ff

of

M. A.

c.

C;. 1:.

f.

Univ.

N.,

A

635. (1954) J 747. nfcf.

1970~

g.

251.

Chcm.,

(1957) 1292. 77 (Ifj_‘j5) 28 (1956) 33H.

30 (rgf3.t) I.tG.

29

.%lC.,

5502.

.47rcd. Chirr1. Ackc,

42

(1rJGt))

ICXJ-I

18