Evaluation of Adsorbents for the Ta-178 Generator - American

10 Evaluation of Adsorbents for the Ta-178 Generator R. D . N E I R I N C K X — D e p a r t m e n t o f Radiology, H a r v a r d M e d i c a l S c h o o l ,

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 14, 2016 | http://pubs.acs.org Publication Date: January 30, 1984 | doi: 10.1021/bk-1984-0241.ch010

Boston, MA 02115 J.

TRUMPER—Soreq

A.

LEBLANC

Nuclear Research Center, Yavne, Israel

and P. C . J O H N S O N — N a t i o n a l Air and Space A d m i n i s t r a t i o n , Life Sciences

D i v i s i o n , H o u s t o n , TX 77058

The c u r r e n t l y used Ta-178 generator is based on a r a d i a t i o n s e n s i t i v e adsorbent and can be eluted about 5 0 times before W-178 breakthrough becomes unacceptable. We evaluated a s e r i e s of i n o r g a n i c and organic adsorbents as support f o r t h i s generator. Hydrated inorganic m a t e r i a l s adsorb tantalum very s t r o n g l y from most aqueous s o l u t i o n s and none was found u s e f u l f o r the W-178/Ta-178 generator. Tantalum comp l e x i n g agents are not able to desorb tantalum without d i s s o l v i n g the adsorbents to an a p p r e c i able extent. C h e l a t i n g r e s i n s with a high affinity f o r W were i n v e s t i g a t e d because they could reduce the W-178 breakthrough. They a l s o adsorb tantalum too s t r o n g l y to be s u i t a b l e as substrates f o r the Ta-178 generator.The Bio-Rad AG1x8 system was found to be s u p e r i o r to the other tested systems. The e f f e c t s of a u t o c l a v i n g , complexant a d d i t i v e s and prolonged e l u t i o n on the Ta-178 y i e l d were measured and the chemical breakdown products quantitated. The usefulness of generator-derived s h o r t - l i v e d r a d i o n u c l i d e s i s w e l l e s t a b l i s h e d . The p r i n c i p a l advantages are the opportunity to perform r a p i d repeat s t u d i e s a f t e r various i n t e r v e n t i o n s and the use of high l e v e l s of a c t i v i t y without s u b j e c t i n g the p a t i e n t to an unacceptable r a d i a t i o n dose. S p e c i a l detectors are necessary f o r the d e t e c t i o n of these high a c t i v i t i e s of r a d i o n u c l i d e s s i n c e the standard Anger-camera i s not able to handle such high count r a t e s . One i s p r a c t i c a l l y l i m i t e d to m u l t i - c r y s t a l cameras or gas cameras l i k e the multi-wire p r o p o r t i o n a l (MWPC) or the gas s c i n t i l l a t i o n counters. This implies that the electromagnetic r a d i a t i o n of the r a d i o n u c l i d e should p r e f e r a b l y be of low energy, as these are most s u i t a b l e

0097-6156/ 84/ 0241 -0151 $06.00/ 0 © 1984 A m e r i c a n C h e m i c a l S o c i e t y

Knapp and Butler; Radionuclide Generators ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

152

RADIONUCLIDE GENERATORS

f o r e f f i c i e n t d e t e c t i o n with gas d e t e c t o r s . Such low-energy electromagnetic r a d i a t i o n can be found i n the c h a r a c t e r i s t i c x-rays of heavy elements. Tantalum-178 (Ta-178) i s a s h o r t - l i v e d r a d i o n u c l i d e ( T ^ -


2

9.3 min) that decays with emission of c h a r a c t e r i s t i c hafnium x-rays which are e f f i c i e n t l y detected by the MWPC. The usefulness of Ta-178 l i e s mainly i n the low p a t i e n t r a d i a t i o n - d o s e per mCi i n j e c t e d . The high a c t i v i t i e s that can be i n j e c t e d generate the high photon f l u x e s that allow an accurate e v a l u a t i o n of f a s t p h y s i o l o g i c processes. The p r i n c i p a l use of Ta-178 has been i n the assessment of the l e f t v e n t r i c u l a r e j e c t i o n f r a c t i o n (1_>2) · A generator f o r the production of Ta-178 has been described e a r l i e r (1). I t i s based on an organic anion-exchange r e s i n which i s s e n s i t i v e to r a d i o l y s i s . The d i s t r i b u t i o n c o e f f i c i e n t f o r tungsten (W) under the s e p a r a t i o n c o n d i t i o n s i s low (_2), which r e s u l t s i n increased W-178 breakthrough a f t e r approximately 50 c o l l e c t i o n s . Furthermore, the e l u a t e has not p r e v i o u s l y been evaluated f o r organic r e s i n breakdown products. T h i s paper summarizes the r e s u l t s of a thorough e v a l u a t i o n of the e x i s t i n g Ta-178 generator and an e v a l u a t i o n of a l t e r n a t i v e adsorbents, most of them i n o r g a n i c , as generator support media. Experimental Radionuclide P r o p e r t i e s of Ta-178. Tantalum-178 i s formed from the decay of i t s parent W-178 ( T j y ) h a l f - l i f e of 9.3 minutes y i e l d i n g s t a b l e Hf-178. The decay of the parent i s o t o p e (W-178) occurs e n t i r e l y by e l e c t r o n capture to the 9.3 minute Ta-178 s t a t e , without feeding the h i g h s p i n Ta-178 isomer ( h a l f - l i f e 2.4 h r s ) . In Ta-178 decay, 99.2% of the d i s i n t e g r a t i o n s proceed by e l e c t r o n capture and 0.8% by p o s i t r o n emission. E l e c t r o n capture r e s u l t s i n a 61.2% branch to the ground s t a t e of Hf-178 and 33.7% to the f i r s t e x c i t e d s t a t e at 93.1 keV. The balance, 4.3%, feeds hafnium l e v e l s between 1175 and 1772 keV. The most prominent f e a t u r e s of the energy spectrum of t h i s r a d i o n u c l i d e are the hafnium c h a r a c t e r i s t i c x-rays with energies between 54.6 and 65.0 keV. =

2

1

,

7

d

9 a

n

d

h

a

s

a

2

M a t e r i a l s . A number of i n o r g a n i c and organic adsorbents were evaluated. A l l the i n o r g a n i c m a t e r i a l s are hydrates and were evaluated i n combination with i n j e c t a b l e aqueous s o l u t i o n s . Complexing agents were added to some eluents i n order to reduce tantalum a d s o r p t i o n . C h e l a t i n g r e s i n s , such as the p y r o g a l l o l formaldehyde copolymer, were tested f o r t h e i r a d s o r p t i o n of tungsten. The adsorption of tantalum onto non-hydrated adsorbents such as the organic adsorbent Bio-Rad AGlx8 and s i l y l a t e d s i l i c a were evaluated.



10.

NEIRINCKX ET AL.

Adsorbents

for the Ta-178

153

Generator

The f o l l o w i n g chromatographic i n o r g a n i c adsorbents were donated by A p p l i e d Research SPRL (Belgium): hydrous t i t a n i u m oxide, t i t a n i u m oxide-hydrogen peroxide hydrate, hydrous zirconium oxide, hydrous f e r r i c oxide, hydrous s t a n n i c oxide, polyantimonic a c i d , s i l i c i c a c i d , hydrous chromium oxide, hydrous manganese d i o x i d e , zirconium phosphate, t i n phosphate, Phomix (20% ammonium phosphotungstate i n zirconium phosphate), S i p h o z i r (zirconium p h o s p h a t e - s i l i c a t e ) , chromium phosphate, t i t a n i u m phosphate, molybdenyl f e r r o c y a n i d e , zirconium f e r r o c y a n i d e , f e r r i c f e r r o c y a n i d e and K-Co f e r r o c y a n i d e . Alumina was obtained from Woelm (Eschwege, Germany). Tungsten c a r b i d e , non-chromâtοgraphic, was obtained from P f a l t z and Bauer (Stamford, Conn.). Tungsten d i s u l f i d e was obtained from Alfa-Ventron (Danvers, Mass.). Bio-Rad AGlx4A was obtained from Bio-Rad (Richmond, Ca.). Some i n o r g a n i c m a t e r i a l s were synthesized i n our l a b o r a t o r y . T h i s group included t u n g s t i c a c i d , C a F and S r F ^ c o a t e d A l ^ , anhydrous Sn0 , T i 0 , S i 0 , 2

2

2

2

CrOg, Mn0 , t i n phosphate, zirconium phosphate, t i t a n t i u m 2

phosphate, molybdenyl f e r r o c y a n i d e , zirconium f e r r o c y a n i d e and f e r r i c ferrocyanide. with a B 0 2

of

3

Tungstic a c i d was produced by h e a t i n g

WO^

f l u x to 1,200°C, c o o l i n g the melt to 800°C at a r a t e

2°C/hour and then to room temperature.

The C a F - or

S r F - c o a t e d A1 0~

2

were prepared by treatment of an A1 0~ 2 + 2 + adsorbent, saturated with Ca or Sr with a NaF s o l u t i o n . C o n t r o l l e d pore g l a s s beads (237 A mean diameter) were obtained from E l e c t r o n u c l e o n i c s , Inc. ( F a i r f i e l d , NJ). S i l a n e Z-6020 was obtained from Dow-Corning. Two kinds of chelate r e s i n were synthesized and evaluated: A pyrogallol-formaldehyde copolymer 03,4) and a copolymer of alphabenzoin oxime with formaldehyde. Bio-Rad AGlx8 200-400 mesh was used as adsorbent to evaluate the published generator method ( 1 ) . S i l y l a t e d s i l i c a g e l was prepared according to the procedure of Leyden, et a l ( 5 ) . F i n e g r a i n s of c o n t r o l l e d - p o r e g l a s s beads (CPG) were heated f o r three hours with 100 ml of a 10% s o l u t i o n of Z-6020 s i l a n e i n toluene. The f i l t e r e d and toluene-washed product was d r i e d overnight at 80 C and used as a tungsten-adsorbent. ?

9

Determination of P a r t i t i o n C o e f f i c i e n t s (Kp).

9

The Kp values of W

and Ta between the adsorbents and v a r i o u s mobile phases of i n t e r e s t were measured by batch e q u i l i b r a t i o n . The f i r s t adsorbent was p r e - e q u i l i b r a t e d three times with the l i q u i d phase, and the supernate decanted. The batch e q u i l i b r a t i o n was performed using 100 mg of adsorbent and 5 grams of mobile phase, to which a W-178-Ta-178 mixture was added. The two phases were then shaken f o r 10 minutes by means of a Hematec A l i q u o t mixer.


154


A f t e r c e n t r i f ligation, samples from each phase were analyzed f o r W-178 and Ta-178 u s i n g a Ge ( L i ) detector coupled to a Nuclear Data ND60 Y-spectrophotometer. Tantalum-178 was quantitated using i t s 93 keV gamma-ray. A f t e r c o r r e c t i o n f o r p h y s i c a l decay, the Kp values are c a l c u l a t e d as the r a t i o of the c o n c e n t r a t i o n s of the element i n the s t a t i c and the mobile phase ( 2 ) . Since the concentrations are p r o p o r t i o n a l to the r a d i o a c t i v i t y l e v e l


=

a c t i v i t y of r a d i o n u c l i d e / g adsorbent a c t i v i t y of r a d i o n u c l i d e / g mobile phase

where the adsorbent i s always weighed as an a i r - d r i e d powder. Tungsten-178 was quantitated a f t e r both f r a c t i o n s were allowed to decay f o r 90 minutes and by counting the e q u i l i b r i u m a c t i v i t y of Ta-178 a s s o c i a t e d with the W-178. The Kp-values were c a l c u l a t e d as f o r tantalum. Adsorption S t u d i e s .

The i n o r g a n i c adsorbents l i s t e d above were -3 evaluated with the f o l l o w i n g non-complexing e l u e n t s : 10 Ν H C l , 0.1N

NaOH, 0.25% Na HP0 .7H 0, 0.9% NaCl and 0.1% NaHS0 . The 2

4

2

3

adsorption of W and Ta onto organic adsorbents was a l s o e v a l uated. The W and Ta adsorption onto the pyrogallol-formaldehyde r e s i n was evaluated with aqueous mobile phases as a f u n c t i o n of pH. The Kp of W and Ta between s i l i c a or s i l y l a t e d s i l i c a and mobile phases c o n t a i n i n g d i l u t e HCl or 1% NaF were determined. An attempt to improve the adsorption of W onto Dowex 1x8 was made by converting the loaded W-178 a c t i v i t y to phosphotungstate, e i t h e r by r e c r y s t a l l i z i n g the phosphotungstate and u s i n g i t s HCl s o l u t i o n s or by forming i t i n s i t u by means of 3 ^ direct H

e v a l u a t i o n of t h i s s o l u t i o n .

P 0

a

n

d

The Kp values f o r W and Ta between

Bio-Rad AGlx4 and HCl s o l u t i o n s of d i f f e r i n g n o r m a l i t y were a l s o -2 -1 determined. The e f f e c t of the a d d i t i o n of 10 M or 10 M ^PO^ to the 0.1 Ν HCl mobile phases was measured. The Kp values f o r W and Ta between e i t h e r HCl or NaF s o l u t i o n s and the c h e l a t i n g r e s i n Chelex 100 were determined as a f u n c t i o n of the pH of the mobile phase. The adsorption of W and Ta onto i n o r g a n i c adsorbents from mobile phases c o n t a i n i n g f l u o r i d e was a l s o s t u d i e d . The Kp values o f W and Ta between f l u o r i d e c o n t a i n i n g aqueous phases and Mn0 , Ti-phosphate, S i 0 s i l y l a t e d S i 0 and S r F were determined 2

2 >

2

2

as a f u n c t i o n of the pH of the mobile phase. the

r a t e of adsorption of W and Ta onto Z r O

?

A study was made of from a 0.1%


10.

NEIRINCKX ETAL.

Na-oxalate

solution

Adsorbents

for

the Ta-178

155

Generator

and onto MnO^ from 1% NaF s o l u t i o n s .

A

study of the r a t e s of d e s o r p t i o n of W and Ta from MnO^ by means of

1% NaF s o l u t i o n s was made.

D i s t i l l a t i o n Generator. I r r a d i a t e d tantalum f o i l s were d i s s o l v e d i n HF + mOy the s o l u t i o n converted to 29N HF and heated to


b o i l i n g i n an a l l - T e f l o n d i s t i l l a t i o n apparatus. Nitrogen was used as a c a r r i e r - g a s to d i s t i l (W-178) WF^ which could be used to generate the n o n - v o l a t i l e (Ta-178)TaF,_.

T h i s would then be

i s o l a t e d by vacuum manipulation of the WF^. Further E v a l u a t i o n of the E x i s t i n g Ta-178 Generator. Shielded Ta-178 generators of 2 cc bed s i z e that can be e l u t e d i n a short time by means of vacuum a s p i r a t i o n were prepared i n the Squibb M i n i t e c c o n f i g u r a t i o n . Generators were b u i l t u s i n g Bio-Rad AGlx8 as the adsorbent. The e f f e c t s of eluent a c i d i t y and hydrogen peroxide c o n c e n t r a t i o n , a u t o c l a v i n g , column bed s i z e v a r i a t i o n , t o t a l eluent volume used and eluent a d d i t i v e s on the breakthrough of W-178 and the y i e l d of Ta-178 were evaluated. The e l u a t e was analyzed f o r p o s s i b l e organic r e s i n - d e g r a d a t i o n products by means of gas-chromatography. In order to q u a n t i t a t i v e l y evaluate the presence and magnitude of the impurity i n s u c c e s s i v e e l u t i o n s , twelve " c o l d " standard columns were loaded with Bio-Rad AGlx8 r e s i n and subjected to a standard W-178-loading procedure, except that no W-178 was present i n s o l u t i o n . The e l u t i o n s were performed with 0.15 Ν HCl + 0.01% H ^ . At 1, 3, 11, and 38 days a f t e r p r e p a r a t i o n , three e l u t i o n s of 1 ml each were c o l l e c t e d from each column. The pH of the samples were adjusted to 12 as r e q u i r e d f o r the gas chromatography procedure. Q u a n t i t a t i o n was by flame i o n i z a t i o n a f t e r the gas chromatographic s e p a r a t i o n . Results The r e s u l t s of the Kp determinations are shown i n Tables I-IV. In Table I the data f o r systems that s t r o n g l y adsorbed both W and Ta are summarized. Table I I contains data on those systems which s t r o n g l y adsorb only Ta. In Table I I I the systems that p o o r l y adsorbed W are d e s c r i b e d . The e f f e c t of a c i d i t y on the adsorption of W and Ta onto a pyrogallol-formaldehyde c h e l a t e r e s i n i s summarized i n Table IV. The Kp values of W and Ta between s i l i c a or s i l y l a t e d s i l i c a and 1% NaF s o l u t i o n s of d i f f e r e n t pH values are summarized i n F i g u r e 1 ( l i n e s 3 and 3A). The Kp values f o r the same adsorbents but u s i n g d i f f e r e n t concentrations of HCl i n the eluent are summarized i n Table V.


156

RADIONUCLIDE

GENERATORS


T a b l e I . Kp V a l u e s f o r W a n d T a B e t w e e n V a r i o u s E l u e n t s and I n o r g a n i c A d s o r b e n t s w i t h a H i g h A f f i n i t y f o r Both Elements Adsorbent/ Eluent Ti0 .H^0 2

*DTa Fe 0 /^)W 3

^Ta S b

T

22 ° S

/ K

H 0

0.1N NaOH

0.25% P04

0.9% NaCl

>2500

>500

59

>1300

>1300

>1000

>200

>400

>140

>300

>350

>300

>2400 >500

>1000 >250

>125 >125

>800 >200

>800 >170

>600 >200

>900 >200

>800 >200

o

0.1% NaHSO

2

DW

2

10 Ν HCl

DW

>250 >100

DTa MnO

A w *DTa

2100 >350

95 >200

800 >300

5600 >800

275 >150

140 >110

380 >200

1100 >200

1500

125

470

800

>140

>140

>90

>60

Ti-phosph/ W Ta Fe(lll)/ ferrocy/ iW Ta ZrO

/K

2 DW Ta

>100

>400

>250

>250

>200

>100

>50

>50


10.

NEIRINCKX ET AL.


Table I I .

the Ta-178

157

Generator

K^ of Tantalum Between Various Eluents and Inorganic Adsorbents with a High A f f i n i t y f o r Tantalum

3

1θ" Ν HCl

0.1N NaOH

0.25% P0.34

0.9% NaCl

0.1% NaHS0

TiO SnO^CCaCip

>200 >200

>30 >40

>60 >200

>150 >250

>300

>60

>70

Zr(ferrocy)

>250

>50

Ni(ferrocy)

>200

>70

Ti(ferrocy) K-Co(ferrocy)

>300 >300 >100

>90 >180

3

10" N HCl

SnO SiO^ Neutral A l 0 Cr0 Zr-phosph Sn-phosph Tungsten Carbide Phomix Siphozir Cr-phosph Cu-ferrocy MoO«(ferrocy) TiO, A l 6 /CaF o

2

3

2

3 0

>100

K^ Values of W Between Various Eluents and Inorganic Adsorbents with Low A f f i n i t y f o r Tungsten

Adsorbent/ Mobile Phase

2 3

for

Absorbent/ Mobile Phase

Table I I I .

ws

Adsorbents

o

3

30 27 30 2 15 4

H 0 2

68

44 14

5 34 53 3 8 7 95 3 6

110

0.1N NaOH

0.25% P0.34

0.7% NaCl +0.2% NaHC0

3

0.9% NaCl

0.1% NaHSO,

120 3

18

6

5

8 3 89 51

55 28

3 96 78

55 35

1 17 12 4 10

36

6

12

24

10 3 8 2

17 6 15 24

41 7 6 2 16 8

21 28 20 2


6


Table IV.

^ o f W and T a Between P-F R e s i n and H C l S o l u t i o n s

- l o g Ν(HCl)

h'


Adsorption

1 2 3 4

T a b l e V.

W Adsorption

Desorption

210 310 200 220

2,500 3,250 3,900 2,850

285 420 490 350

2,000 2,000 2,000 2,000

o f W and T a Between S i l i c a o r S i l y l a t e d and Aqueous D i l u t e H C l

V

- l o g Ν(HCl)

Adsorption

Silylated 650 19 28

Silica

Ta

W

Adsorption Desorption

1 2 3

Desorption

Desorption

silica

>5,000 130 16

>500 >500 >20

>500 >100 >10

>20 >20 >20

>200 >500 >1,000

Silica 1 2 3

26 30 56

450 850 >5,000



NEIRINCKX ETAL.

Adsorbents

for the Ta-178

Generator

159

Figure 1. D i s t r i b u t i o n c o e f f i c i e n t s (K ) of W and Ta between SrF2, s i l y l a t e d Si02 or S1O2 and aqueous NaF s o l u t i o n s as a f u n c t i o n of the pH of the mobile phase. D


160


The r e s u l t s of the a d s o r p t i o n experiments u s i n g Bio-Rad AGlx8 with the W-phosphotungstate were negative because stronger Ta-adsorption occurred w i t h these phosphate-containing s o l u t i o n s . The r e s u l t s of the Kp determination f o r W and Ta between Bio-Rad AGl-x4 and HCl s o l u t i o n s of d i f f e r e n t normality are summarized i n F i g u r e 2. The e f f e c t of the a d d i t i o n of ^PO^, to the 0.1 Ν HCl


mobile phase i s a l s o i n d i c a t e d .

The r e s u l t s of the Kp

determinations f o r W and Ta between Chelex 100 and d i l u t e HCl s o l u t i o n s are shown i n Table VI. The r e s u l t s f o r Chelex 100 using 1% NaF s o l u t i o n s of v a r y i n g pH are summarized i n Table V I I . The Kp of W and Ta between MnO^ and aqueous s o l u t i o n s of d i f f e r i n g NaF concentrations and pH are summarized i n F i g u r e 3. The Kp values f o r W and Ta between Titanium phosphate and e i t h e r 1% NaF or 0.1% NaF Table V I I I .

s o l u t i o n s as a f u n c t i o n of pH are shown i n

The Kp values as a f u n c t i o n of pH f o r W and Ta

between SrF^ and 0.1% NaF ( l i n e s 1 and 1A). Si0

2

s o l u t i o n s are summarized i n F i g u r e 1

In F i g u r e 1 the Kp values of W and Ta between

( l i n e s 2 and 3A) or s i l y l a t e d S i 0

2

( l i n e s 2 and 2A) and

1%

NaF

s o l u t i o n s as a f u n c t i o n of pH are summarized. The r e s u l t s of the determination of the adsorption r a t e s of W and Ta onto Z r 0 and Mn0 are shown i n F i g u r e 4. L i n e s 1 and 2 2

2

show the a d s o r p t i o n of W and Ta onto Mn0

2

from 1% NaF

L i n e s 3 and 4 d e p i c t the adsorption of W and Ta by Z r 0 0.1%

sodium oxalate s o l u t i o n .

solutions. 2

from a

L i n e s 5 and 6 of F i g u r e 4 show

the d e s o r p t i o n of W and Ta from Mn0

2

by 1% NaF s o l u t i o n s .

Using

the M i n i t e c c o n f i g u r a t i o n , a f u l l bolus of Ta-178 was e l u t e d from the 2 cc Bio-Rad AGl-x8 columns by means of 1.5 ml of HCl 0.15 Ν + 0.01% Η 0 · The e l u t i o n i s performed with an evacuated v i a l 2

2

and takes only 15 seconds. The adsorbent bed can be l e f t dry between e l u t i o n s . In the d i s t i l l a t i o n experiment, (W-178)WF could not be 6

d i s t i l l e d from the 29 Ν HF s o l u t i o n s , using the a l l - T e f l o n d i s t i l l a t i o n apparatus. The e l u t i o n y i e l d f o r Ta-178 from Bio-Rad AGl-x8 by means of 1.5 ml of 0.10 Ν HCl + 0.01% H ^ or 1.5 ml of 0.15 Ν HCl + 0.01% H 0 2

2

was

33% and 52%, r e s p e c t i v e l y .

breakthrough

The Ta-178 y i e l d s and

values obtained with 2 ml of 0.15

v a r i a b l e amounts of H 0 o

o

are shown i n Table IX.

W-178

Ν HCl c o n t a i n i n g Table X shows



10.

NEIRINCKX ET AL.

Adsorbents

for

the Ta-178

αΟΙ 0J03

161

Generator

O.IO

Ν HCL F i g u r e 2. D i s t r i b u t i o n c o e f f i c i e n t s ( Κ ) o f W and Ta b e tween B i o - R a d A G l x 4 and aqueous H C l s o l u t i o n s a s a f u n c t i o n of H C l c o n c e n t r a t i o n . β

Table V I .

Kp o f W and T a Between C h e l e x 100 and M o b i l e Phases o f V a r y i n g H C l C o n c e n t r a t i o n (10 Desorption) f

_

pH

W

0.6 0.8 1.0 1.1 1.3 4.8 9.0

950 1,250 3,000 3,000 4,000 75 10 10

Ta 100 150 400 500 40 10 20


162

RADIONUCLIDE

Table V I I . ^

GENERATORS

o f W and T a Between C h e l e x 100 and 1% NaF Aqueous S o l u t i o n s a s a f u n c t i o n o f pH (10 desorption)


f

pH

W

1.8 2.0 3.1 3.9 5.1 6.0 7.4 8.3 8.7 9.9

1,600 300 350

Ta 85 100 80 90 40 50 25 20 10 2

-130 170 30 20 10 1

ΒL o f W and T a Between T i - p h o s p h a t e and fi l u o r i d e s o l u t i o n s a s a f u n c t i o n o f pH

Table V I I I .

0.1% NaF

1% NaF pH

pH W

0.4 0.8 1.3 1.6 2.1 4.0 5.4 6.0 6.4 6.6

42 150 90 270 320 760 920 1,900 530 460

W

Ta 22 50 70 150 200 140 120 170 370 >500

1.1 1.5 2.0 3.0 3.4 4.3 4.7 5.0 5.1 5.2

230 890 360 420 450 780 1,250 1,450 1,100 1,100

Ta >250 410 175 160 160 200 340 340 320 330


Adsorbents

NEIRINCKX ET AL.

for

the Ta-178

Generator

IQOOO

1000

Ι


ο

100 γ

ΙΟ

4 -PH-

Figure 3. D i s t r i b u t i o n c o e f f i c i e n t s ( K ) of W and Ta be tween Mn0 and aqueous NaF s o l u t i o n s of d i f f e r e n t concen t r a t i o n as a f u n c t i o n of the pH of the mobile phase. D

2

1,000

\////////////////////^^ (5) W- desorption M n 0

2

ο 100

(2) Τα-adsorption

Mn0

2

10

f

-L 10'

-L 30' Time of equilibration

60'

Figure 4. Adsorption r a t e of W and Ta onto Mn02 and Zr02 from aqueous 1% NaF s o l u t i o n s and desorption of these elements from MnOo.


164



the i n f l u e n c e of a u t o c l a v i n g of the loaded AGl-x8 generator on the Ta-178 y i e l d and radiochemical p u r i t y (RCP)· To i n h i b i t the m i g r a t i o n of p a r t i c l e s during the a u t o c l a v i n g , an intermediary f i l t e r was added 5 mm under the top f i l t e r of the column. The e f f e c t of a u t o c l a v i n g on the Ta-178 y i e l d and RCP f o r t h i s type of column i s summarized i n Table XI. The r e s u l t s of an exhaustive e l u t i o n of a 1 cc Ta-178 generator based on Bio-Rad AGlx8 i s shown i n Table X I I . Each e l u t i o n was performed with 1 ml of HCl 0.15N + 0.01% H ^ . Several mixtures of 0.15 Ν HCl with other components were evaluated as eluents f o r a 2 cc Ta-178 generator. The r e s u l t s are summarized i n Table X I I I . Trimethylamine was i d e n t i f i e d as a product of the decomposition of the Bio-Rad AGl-x8 anion-exchange r e s i n . The q u a n t i t a t i v e r e s u l t s obtained by gas-chromatography and FID are summarized i n Table XIV. Discussion Using a 0.10

Ν HCl + 0.01%

H ^

as e l u e n t , the L i f e Sciences

D i v i s i o n of the N a t i o n a l Aeronautics and Space A d m i n i s t r a t i o n (NASA) has s u c c e s s f u l l y operated a l a r g e number of Ta-178 generators based on Bio-Rad AGlx8 and has s u c c e s s f u l l y t e s t e d them i n human s u b j e c t s 05). U l t i m a t e l y , t h e i r i n t e n t i o n i s to use these f o r e v a l u a t i o n of c a r d i a c f u n c t i o n of astronauts i n space. The only published Ta-178 generator i s based on adsorption of W-178 on an organic anion-exchanger and e l u t i o n of the daughter i s o t o p e by means of a d i l u t e HCl e l u e n t , c o n t a i n i n g a small amount of H^O^. The e l u a t e can e a s i l y be converted to an i n j e c t a b l e s o l u t i o n and the Ta-178 y i e l d s i n 1 ml eluent volume are higher than 50%. However, the W-breakthrough i n c r e a s e s to more than 0.1% a f t e r about 50 c o l l e c t i o n s . The e a r l y breakthrough and the r a d i o l y t i c i n s t a b i l i t y of organic adsorbents are the main drawbacks of t h i s system. An attempt to c o r r e c t these shortcomings by u s i n g a more r a d i a t i o n - r e s i s t a n t i n o r g a n i c adsorber or with any other adsorbent that would adsorb W more s t r o n g l y than Bio-Rad AGlx8 d i d not lead to a procedure that was s u p e r i o r to the o r i g i n a l system. Many i n o r g a n i c adsorbents have a high a f f i n i t y f o r tungsten but t y p i c a l l y a l s o adsorb tantalum very s t r o n g l y . I t was noted that Ta-178 which had grown i n from W-178 while the l a t t e r was adsorbed was very s t r o n g l y r e t a i n e d by a l l the i n o r g a n i c adsorbents. The reason f o r t h i s strong Ta b i n d i n g may r e s u l t from i s o e l e c t r o n i c t r a n s i t i o n of the W-178 which probably does cleave any chemical bonds between the daughter isotope Ta-178 and the atoms or groups of the molecule. 2Since most of the experiments have been performed with WO^ , the r e s u l t a n t Ta species may be expected to remain oxygenated because Ta 5 d - o r b i t a l s overlap s t r o n g l y with oxygen 2 p - o r b i t a l s to give s u b s t a n t i a l ^-bonding.


Adsorbents

NEIRINCKX ET AL.

for the Ta-178

165

Generator

Table IX. Ta-178 Y i e l d and W-178 Breakthrough from Bio-Rad AGlx8 as a Function of the H 0 -Concentration 0

% H 0


2

0

W-178 Breakthrough

Ta-178 Y i e l d

2

(%)

J

(xio ) 5 0.2 N.A.

Evaluation of Adsorbents for the Ta-178 Generator - American

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