New SPE column packing material retention assessment method and its application for the radionuclide chromatographic separation

Introduction Among the column packing materials used for solid phase extraction SPE chromatography the extractant liquid organic extractant and/or a liquid ion-exchanger of high molecul

New SPE column packing material: Retention assessment method

and its application for the radionuclide chromatographic separation

Le Van So*, N Morcos

Radiopharmaceutical Research Institute, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights,

P.M.B 1, Menai, NSW 2234, Australia

(Received October 29, 2007)

The preparation of the OASIS®-HLB sorbent based solid phase extraction (SPE) resins and their application for the 177 Lu radioisotope separation were investigated Di-(2-ethylhexyl) orthophosphoric acid (HDEHP) impregnated OASIS-HLB sorbent based SPE resins (OASIS-HDEHP) were successfully developed from this investigation The wettable porosity structure of the moderately extractant impregnated OASIS-HDEHP resins is favorable for the effective diffusion of polar and ionic solutes giving good separation performance Its good wetting ability offers ease of packing into conventional chromatographic columns Their off-gassing-free operation makes OASIS-HDEHP columns good for long term use with highly consistent elution dynamics (several dozens of separations perfectly achievable on the same column) The simple method for the capacity factor

(k’) evaluation was developed to facilitate the characterization of the SPE chromatographic resin column A competent procedure using

OASIS-E30RS resin (one member of the OASIS-HDEHP resin group) for the separation of no-carrier added (n.c.a) 177 Lu from the bulk amount of Yb target was developed This separation procedure has showed very good performance with several prominent advantages such as the much shorter separation time (5–6 hours) and high reproducibility Its high adsorption capacity for Yb and Lu makes it ideal for the separation of the bulky sample (50 mg Yb target for the 20 g weight resin column) for the production of the several Ci of 177 Lu radioactivity

Introduction

Among the column packing materials used for solid

phase extraction (SPE) chromatography the extractant

(liquid organic extractant and/or a liquid ion-exchanger

of high molecular weight) coated inert sorbent based

SPE resins are widely used for the inorganic solute

separation These resins have been recently used for

radiochemical separations in radioisotope production

processes Normally, these SPE resins are useful in

reverse phase chromatography which requires a polar

liquid mobile phase for the elution A hydrophobic inert

substrate is currently used to form the SPE resin with a

relevant less hydrophilic extractant This has caused

non-wetting and off-gassing problems during the

column packing and running, respectively The

non-wetting property of this SPE resin type is unfavorable

for the diffusion of polar and ionic solutes to be

separated, so the column separation performance will be

seriously affected Even if the hydrophilic inert substrate

is alternatively used, the non-wetting problem will also

increase if an improper process of the extractant

impregnation is applied If the strongly hydrophilic inert

sorbent is to be applied for SPE resin preparation, then

longer elution times will be experienced due to the

unwanted side effect of strong polar-polar interaction

between the sorbent and polar (or ionic) solutes in

reverse phase chromatography For example the US

patent based separation process using the strongly polar

Amberchrom CG-71 sorbent based LN resin (Eichrom

Technologies) and HCl acid eluent for the separation of

* E-mail: slv@ansto.gov.au

n.c.a 177Lu radioisotope from 5 mg Yb target took around 12 hours.8,9

Logically, an inert substrate rendering a hydrophilic-hydrophobic balanced property will be preferable to overcome the strong interaction and long retention time problems mentioned above Among such expected inert substrates, the OASIS®-HLB sorbent (a hydrophilic-lipophilic balanced co-polymer) was the first choice for preparation of the SPE resin The OASIS ®HLB sorbent

is a macroporous copolymer made from a balanced ratio

of two monomers, the lipophilic divinylbenzene and hydrophilic N-vinylpyrrolidone It provides reverse-phase capability with a special “polar-hook” for enhanced capture of polar solutes and excellent wetting ability.15 This sorbent has the unique capabilities of remaining wetted with water and retaining a wide spectrum of non-polar organic extractant and several liquid ion-exchangers which are used as stationary phase for SPE chromatography Wetting with water into porosity structure of OASIS-HLB sorbent particle is an advantageous feature to facilitate the diffusion process

of polar and ionic solutes during elution with aqueous mobile phase

In this paper the preparation of the OASIS®-HLB sorbent based SPE resins and their application for the

177Lu radioisotope separation are reported The HDEHP impregnated OASIS-HLB sorbent based SPE resins (OASIS-HDEHP) were prepared and their adsorption properties and chromatographic performance are investigated

The basic retention calculation method for SPE

chromatography is also refined to formulate the

generalized equations matching the specific

requirements of the SPE resin development and

application for chromatographic separation

To demonstrate the prominent performance

regarding the predictable chromatographic properties of

OASIS-HDEHP resins, the column separation of n.c.a

177Lu radioisotope from the bulk ytterbium target was

performed The separation of trace level radioactive

impurities from the 176Lu (n,γ)177Lu reaction produced

177Lu solution is well within the capabilities of the

OASIS-HDEHP resin columns.14 The separation of the

bulk Yb target can also be carried out with Eichchrom’s

LN resin (the Amberchrom CG-71 resin substrate

impregnated with HDEHP), however, the performance

of LN resin columns may be affected by the strong

polarity of the acrylic ester based inert resin substrate

leading to long elution times due to the stronger

adsorption of the Yb–Lu pair.8–11 The hydrophilic

Oasis-HLB sorbent based OASIS-HDEHP resin

reported here has surpassed the shortcomings of the LN

resin mentioned above

Experimental

Reagent and material

The commercially available OASIS®-HLB resin

(WATERS’s sample extraction products) with average

particle size of 54.4 µm, pore diameter of 86.0 Å,

specific surface area of 813.0 m2/g15 and

di-(2-ethylhexyl)orthophosphoric acid (97%, BDH) were used

for our di-(2-ethylhexyl)orthophosphoric acid (HDEHP)

impregnated OASIS-HLB sorbent based SPE resins’

(OASIS-HDEHP) preparation The analytical grade

hydrochloric acid, HPLC grade methyl alcohol and

Milli-Q purified water were used for the whole

experimental process The isotopically enriched

176Y2O3 and 176Lu2O3 targets for neutron activation

were purchased from Trace-Sciences International Inc.,

USA.13 The 176Y2O3 target isotopic compositions were

176Yb (97.6%), 174Yb (1.93%), 173Yb (0.18%), 172Yb

(0.22%), 171Yb (0.07%), 170Yb (<0.01%) and 168Yb

(<0.01%) The main lanthanide impurities of this target

were Er (50 ppm), Tm (50 ppm) and Lu (50 ppm)

Apparatus, radioactivity and radionuclide calibration

The radioactivity of the different radioisotopes was

calibrated using a Capintec dose calibrator

Radioactivity measurement and radionuclide

identification were carried out using an Ortec

gamma-ray spectrometer coupled with HpGe detector The

gamma-ray energy and radioactivity calibration of this

analyzer system was performed using a standard 152Eu

radioisotope solution

Radioactive solutions

The radioactive 177Lu+175Yb solutions were obtained by the reactor thermal neutron irradiation of

176Yb2O3 A quartz ampoule containing adequate amount of 176Yb2O3 target was irradiated with the 5.1013 n.cm–2.s–1 thermal neutron flux of the High Flux Australian reactor (HIFAR) for 10 days A 24-hour cooling period was needed to let all 177Yb (T1/2=1.91 hours) radionuclide, which formed via 176Yb(n,γ)177Yb,

to be transformed to 177Lu via beta-particle decay The irradiated target was then dissolved in about 10 ml 6M HCl solution, added with some drops of H2O2 (30%) solution with gentle heating on the hot plate Then the target solution underwent several cycles of the dry evaporation – water added reconstitution Finally the target solution was obtained by constituting with 2 ml 0.1M HCl solution An aliquot of some microliter volume was taken out from the target solution for gamma-ray spectrometry regarding the determination of target radioactivity and radiochemical separation yield The convenient assessment of the 175Yb isotopic decontamination factor and the Yb element content in

177Lu eluate fractions could be made using data collected from gamma-ray spectrometry measurement of the above mentioned target sample and that of different column elution fractions Due to the 174Yb(n,γ)175Yb reaction induced from the 174Yb nuclide content (1.93%) in the 176Yb target, the significant amount of

175Yb radioisotope produced along with 177Lu will be useful for the spiking purpose to track the elution profile

of the remaining macro-quantity of non-radioactive Yb target

Preparation of the OASIS-HDEHP resins

Appropriate amount of dry OASIS®HLB resin was measured into a glass beaker and soaked in the given amount of methyl alcohol containing a relevant amount

of HDEHP extractant The mixture was shaken in an ultrasonic water bath with vacuum application for 20 minutes and then evaporated to dryness in a RotaVapor® system The rotation speed of 50–70 rpm and the heating bath temperature of 40 °C were applied A given amount

of the methyl alcohol/ethyl alcohol mixture (volume ratio 2:1) was added to the dried resin to form a pasty consistency followed by drying The drying process continued until a final resin product of free flowing form was obtained

Density measurements

The weight density of resin, ρRe was determined by standard methods using the volume-metric flask at

20 °C The weight density of resin column, ρc was determined with a given dry resin weight packed into a

graduated chromatographic column eluted with the

eluent pressure difference of 660 mm Hg (equivalent to

8.8 m H2O column height) The ρc value was calculated

from the weight of the dry resin packed and the resin

bed volume in the graduated column

Investigation of the solute sorption

and SPE chromatographic separation

Determination of the weight distribution coefficient,

D Re.W , Lu and Yb sorption as a function of the HCl

eluent solution molarity: Four types of OASIS-HDEHP

resins were investigated:

OASIS-E16RS: OASIS-HDEHP resin containing

16.0% HDEHP (w/w)

OASIS-E30RS: OASIS-HDEHP resin containing

30.0% HDEHP (w/w)

OASIS-E36RS: OASIS-HDEHP resin containing

36.0% HDEHP (w/w)

OASIS-E41RS: OASIS-HDEHP resin containing

41.0% HDEHP (w/w)

Six vials containing 15 ml HCl solution each (1.0M,

2.0M, 3.0M, 4.5M, 6.0M and 7.5M), itself containing

the mixture of 0.5 mg Yb + 2.0 µg Lu spiked with

radioactive 175Yb and 177Lu radioisotopes were used

Then 50 mg portions of each resin were weighed into

each prepared solution vial The vials were shaken in an

ultrasonic bath with vacuum application for 20 minutes

and then shaken in a thermostat water bath at 20 °C

overnight The radioactivity of the resin and solution

were measured and the distribution coefficient was

calculated This D Re.W measurement process with the

use of the dry and wet OASIS-HDEHP resins is shown

in Fig 1

D Re.W value is calculated from the collected data as follows:

⎟⎟

⎞

⎜⎜

=

v

a W

V v a A

D W ( sol / ) / sol

Re

0

Re

where WRe is the resin weight (gram), A0 is the total

amount of the element in the investigated system; V is

the volume of solution in the investigated system (ml),

Vsr is the resin slurry volume (ml), ρsr is the resin slurry weight density

A plot of D Re.W vs eluent solution concentration can

be set up by taking into account the eluent dilution effect

of slurry resin addition with an eluent dilution factor of

(V1/V) In the case of the investigation with the dry

resin, no eluent dilution effect will be taken into account

Determination of the volume distribution coefficient, D Re.V

Lu and Yb sorption as a function of HCl eluent solution: D Re.V is measured from the column elution

profile (the chromatogram at the column outlet)

The D Re.V value is calculated from the elution profile

as follows:

Re Re

.

V V

V V

D V = R− m = Correct

where V m is the total free volume of the column from the top of the resin column to the point at which the solution

leaves the column (ml), VRe is the volume of the resin in

the column (ml), V R is the total volume (including total free volume) of solution corresponding to the top of the peak of respective solute (ml)

Fig 1 Measurement process of D Re.W

The conversion of the resin volume distribution

coefficient D Re.V to the resin weight distribution

coefficient D Re.W: The weight densities used for the

equation formulation are the followings: ρC is the

weight density of column bed (weight of dry resin per

unit volume of column bed, g/ml), ρRe is the weight

density of the resin (weight of dry resin per unit resin

volume, g/ml)

The resin weight distribution coefficient is:

g

ml , phase) liquid the of liliter amount/mil

(Solute

resin) dry the of m amount/gra

(Solute

Re

=

=

W

D

g

ml ,

Re 0

Re

⎟

⎠

⎞

⎜

⎝

⎛

⎟⎟

⎞

⎜⎜

=

V A W

A A D

s

s W

The resin volume distribution coefficient is:

ml

ml , phase) liquid the of liliter amount/mil

(Solute

resin) dry the of liliter amount/mil

(Solute

Re

=

=

V D

ml

ml , Re 0

Re

⎟

⎠

⎞

⎜

⎝

⎛

⎟⎟

⎞

⎜⎜

=

V A V

A A D

s

s V

The conversion equation of the different distribution

coefficients is the following:

Re

Re Re

Re 0

Re Re

0 Re

0

Re

1

ρ ρ

ρ

V sol

sol

sol

sol sol

sol W

D V

A V

A A

V A V A A

V A W A A D

=

⎟

⎠

⎞

⎜

⎝

⎛

⎟⎟

⎠

⎞

⎜⎜

⎝

=

=

⎟

⎠

⎞

⎜

⎝

⎛

⎟⎟

⎠

⎞

⎜⎜

⎝

=

⎟

⎠

⎞

⎜

⎝

⎛

⎟⎟

⎠

⎞

⎜⎜

⎝

=

W

The conversion between the D Re.V and the extractant

volume distribution coefficient (D Ext.V) calculated from

the ρExt weight density, as reported in the literature,1,2,7

does not seem necessary D Ext.V seems to be an apparent

parameter unspecified for the property of the pure

extractant due to the possible variation in the weight

density resulted from the interaction between the

extractant and sorbent substrate on the resin pore

surface

Method for the SPE resin column retention factor (k’) assessment: Based on the basic concept of

chromatography, the column retention factor (k’) is

defined as follows:

phase) mobile the in solute of (amount

phase) stationary the

in solute of (amount

’=

k

V m

D V

V

k’= Re⋅ Re. (2)

where V m is the mobile phase volume in the packed

column, VRe is the stationary phase volume in the

packed column (the SPE resin dry volume), D ReV is the resin volume based volume distribution coefficient For the column packed with dry resin of the weight

of WRe, the VRe value will be:

Re

Re

W

V =

If the column is packed with wet resin, the column

bed volume V C and column bed density ρc , the VRe

value will be:

Re Re

Re

ρ

V W

=

=

With the column bed volume

C

V

ρRe

= and the dry

resin volume

Re

Re

Re ρ

W

V = , the mobile phase volume will

be:

) 1 1 (

Re

Re Re Re Re

−

=

C C

C

Re Re

V

C

C

⋅

−

=

ρ ρ

ρ ρ

From the above equations the following volume ratio can be set up:

) (

) (

) (

Re Re

Re Re Re

Re Re

C C C

C

W V

V

ρ ρ ρ ρ

ρ

ρ

⋅

−

The resin column retention factor (k’) can be now

calculated by putting Eq (3) into Eq (2):

V C

C V

m

D D

V

V

Re

Re

Re

) (

−

=

⋅

=

ρ ρ ρ With the conversion factor:

)

C V

C

ρ ρ

ρ

−

=

the above equation will be simplified as follows:

V

C

With the conversion between D Re.V and D Re.W as

shown in Eq (1), the following equation can be

achieved:

W C

Re

Re

) (

−

⋅

=

ρ ρ

ρ ρ

This is a simple equation for calculation of k’ value

from only two physical constants (ρc and ρRe) and

D Re.W value By giving a conversion factor:

) ( Re

Re

C

C W

C

ρ ρ

ρ ρ

−

⋅

=

the above equation will be simplified as follows:

W

C

It should be mentioned that the conversion Eqs (4)

and (5) do not contain the extractant weight density

(ρExt) which was applied in some recent

publications.1,2,7 The elimination of the role of the ρExt

parameter from the above equations implied to describe

the sorption and chromatographic properties of the

newly formed SPE resin not related to its components

(pure extractant and inert sorbent substrate)

Separation factor assessment: The separation factor

(α) calculation was performed as follows:

) Yb (

) Lu ( )

Yb ( Re

) Lu ( Re ) Yb (

Re

) Lu (

Re

Corrected

Corrected V

V W

W

V

V D

D D

D

=

=

=

α

For practical application, the SPE column containing

10 g OASIS-HDEHP resin was used The retention

factor (k’) or retention volumes and the separation factor

(α) for the separation of Lu and Yb ions were calculated

177 Lu separation processes: OASIS-HDEHP resin containing 30% HDEHP in weight was used for the Yb–

177Lu separation This resin (OASIS-E30RS) is useful for Lu–Yb ion separation and was prepared as follows: For 45.0 g OASIS- E30RS resin preparation, 31.5 g OASIS®-HLB resin was put into a 1 liter glass beaker together with 50 ml methyl alcohol 13.5 g di-(2-ethylhexyl) orthophosphoric acid diluted in 30 ml methyl alcohol was added to the beaker The mixture was shaken in ultrasonic water bath with vacuum application for 20 minutes and then let to evaporate the mixture to dryness in a RotaVapor® system Rotation speed of 50–70 rpm and the heating bath temperature of

40 °C were applied A 2:1 ratio methyl alcohol/ethyl alcohol (30 ml) was added to the dried resin to form a pasty consistency and the drying process was continued until a final resin product of free flowing form was obtained

The glass columns loaded with 5.0–25.0 g OASIS-E30RS resin were used The column loading procedure was applied as follows After soaking the required amount of OASIS-E30RS resin with 0.1M HCl solution

in a glass vial the degassing and wetting of resin was performed by shaking the vial in an ultrasonic water bath for 10 minutes with vacuum application The degassed and well-wetted resin was then packed to the above mentioned columns A peristaltic vacuum pump applied on the outlet of the column was used for eluant delivery The columns were then flushed with 6M HCl solution and reconditioned with 0.1M HCl solution and put into use at any time The separation process flow chart is shown in Fig 2

Fig 2 No-carrier added 177 Lu separation from the bulk amount of 176 Yb2O3 target

The on-line recording of the radio-chromatogram

during the column elution process was achieved by

monitoring the 175Yb+177Lu radioactivity using a

NaI(Tl) crystal scintillation detector coupled to the

LAURA computer software supported radioactivity

counter

Results and discussion

Preparation of the OASIS-HDEHP resins

As shown in Table 1 and Fig 3, coating degrees of

up to 40% HDEHP content in the resin ensured that the

extractant did not break into the mobile phase of

variable acidity The OASIS-HDEHP resin with

impregnating extent higher than 35% became poorly

wettable in the HCl solution of acidity higher than 4.5M

The poor wettability property is assumed to result from

the fully filling of the resin pores with extractant This

fully filling phenomenon not only damages the

wettability of the resin but also decreases the diffusion

kinetics of the solutes in the separation process This

fact has led us to the choice of the extractant moderately

impregnated OASIS-HDEHP resins with impregnating extent lower than 40% in our further investigations All these resins are of free flowing form, wettable and easy to pack into the column To get the best column operation performance, these resins should be gassed off by ultrasonic shaking combined with vacuum application

These resins have very good stability More than 30 Yb/Lu separations were performed on the same OASIS-E30RS resin column without any performance degradations

Distribution coefficients and separation factor

The results of weight distribution coefficient (D Re.W) measurement for Yb3+ and Lu3+ ions in the HCl solutions are shown in Figs 4 and 5 The fact that

increasing D Re.W values for the resins of higher HDEHP contents make the resins of HDEHP contents lower than 30% favorable for the column chromatographic

separation These resins showed the D Re.W values at around lower than 75 for Lu 3+ and 50 for Yb3+ ions in the HCl solution acidities between 2M and 6M

Table 1 Preparation of different HDEHP coated SPE resins

OASIS-HDEHP resins OASIS-E16RS OASIS-E30RS OASIS-E36RS OASIS-E40RS HDEHP weight (g) in 50 ml methanol 6.00 13.50 8.86 11.88

OASIS®-HLB resin weight (mg) 31.50 31.50 15.75 15.75

HDEHP content in the coated resin (%)* 16.00 30.00 36.00 41.20

* After conditioning with 1000 ml water per gram coated resin

** Compared to total HDEHP amount used for coating

Fig 3 HDEHP content in the coated OASIS-HDEHP resin vs that in the reaction mixture A: calculated; B: experimental

Fig 4 Weight distribution coefficient of Yb (D Re.W-Yb) vs HCl solution acidity for OASIS-HDEHP resin coated with variable HDEHP content

Fig 5 Weight distribution coefficient of Lu (D Re.W-Lu) vs HCl solution acidity for OASIS-HDEHP resin coated with variable HDEHP content

Regarding the separation capability of resin, the

achievable separation factor (α) should be as high as

possible The separation factor values presented in Fig

6, which were calculated from the data of Figs 4 and 5,

have showed that the resins of HDEHP contents higher

than 25% offer the best Yb/Lu separation capability with

the HCl solution eluents of concentrations lower than

3.0M It is obvious that the choice of OASIS-E30RS

resin (30% HDEHP content) for the Lu3+/Yb3+ ion pair

separation was confirmed with a separation factor of 1.6

achieved in 3.0M HCl solution as shown in Fig 6

Assessment of capacity factor (k’) and corrected

retention volume (V’ R ) for lutetium and ytterbium

separation using the HDEHP coated

resin OASIS-E30RS

The k’ value calculation is based on two physical

constants (ρc, ρRe) and the weight distribution

coefficient (D Re.W ) The disappearance of the s (%)

coating percentage parameter and the ρExt extractant

weight density from the k’ equation implies that the

effect of the s (%) and ρExt parameters is covered by the

presence of ρc and ρRe parameters The calculated

results using the above equation are listed in Table 2

Due to the possible interaction between sorbent substrate

surface and coated extractant in the SPE resin, the effort

to use the ρExt parameter for the conversion between the

D Re.W parameter and the D Ext.V (the extractant volume distribution coefficient) does not seem useful and

convincible This conversion makes the k’ factor

determination confused To avoid the use of the

physically meaningless D Ext.V parameter non-specified for extractant volume coated in the SPE resin, the resin

volume distribution coefficient, D Re.V (related to the extractant impregnated SPE resin volume) was used for

the k’ factor calculations in our present report This has brought about a more simple equation for k’ factor

assessment and its determination method was compared

to that mentioned in the recent literature.1,2,7

Additionally, the D Re.V parameter can be determined based on the elution profile and the resin weight in the column So the equations (1), (4) and (5) mentioned above, seem more convenient to be used for the practical SPE chromatography

The k’ factor and corrected V’ R retention volume calculation results for OASIS-E30RS resin column are shown in Table 2 and Fig 7 It is obvious that the elution volume of some hundred millilitres from the 10 g weight OASIS-E30RS resin column is quite practical for performing a separation process for the Lu3+/Yb3+ ion pair

Fig 6 Separation factor for Lu–Yb separation vs HCl solution acidity and the HDEHP content of the OASIS-HDEHP resins

Table 2 Physical constants of HDEHP coated resin and the results of the C V and C W of conversion factor calculations

Extractant coating percentage, s (%) (40.00) (40.00) (40.00) 30.00

Resin column bed density, ρc (g/ ml)

Extractant coated resin density, ρ Re (g/ml)

(0.38) (1.15)

(0.37) (1.13)

(0.39) (1.13)

0.40 1.16 )

( Re

Re

C

C W

C

ρ

ρρ −ρ

⋅

W

C

k’ = ⋅ Re. 0 567 ⋅DRe.W 0 55 ⋅DRe.W 0 595 ⋅DRe.W 0 61 ⋅DRe.W

)

C V

C

ρ ρ

ρ

−

V

C

k’ = ⋅ Re. 0 493 ⋅DRe.V 0 48 ⋅DRe.V 0 527 ⋅DRe.W 0 52 ⋅DRe.V

* Data in parentheses are from References 1, 2 and 7 used for identification of the calculation method

Fig 7 Retention factor (k’) and corrected retention volume (V’R) vs HCl eluent acidity for the Yb 3+ /Lu 3+ ion pair separation using the HDEHP

coated OASIS-LHB resin (OASIS-E30RS), OASIS-E30RS resin weight: 10 g; column: 31.8 length × 1.0 cm i.d; Vm = 11.5 ml

Lu 3+ /Yb 3+ ion pair separation

To perform a successful separation, the amount of

solute loaded on the resin column was chosen to

correspond to around 5% of the maximal adsorption

capacity of the resin column In the case of

OASIS-E30RS resin the maximal adsorption capacity is

supposed to equal to the amount of exchangeable H+

ions present in the HDEHP molecule Based on the

chemical formula of HDEHP:

[CH3(CH2)3CH(C2H5)CH2O]2P(O)OH

it is shown that HDEHP contains one exchangeable H+

in each molecule So its ion-exchange capacity could be

of 3.1 meq H+/g HDEHP

One gram OASIS-E30RS resin contains 300 mg

HDEHP So the ion-exchange capacity of

OASIS-E30RS resin will be 0.93 meq H+/g resin The average

gram equivalent of [Yb3++Lu3+] is 58 mg

[Yb+Lu]/meq So, one gram weight resin column of 5%

Yb + Lu solute loading as mentioned above can be loaded with 0.93 (meq/g resin)×5%×58=2.7 mg [Yb3++Lu3+]/g resin

Based on the k’ factor and loading calculation results

achieved above the separations of micro-quantities of

Lu3+ ions from the 30 mg and 50 mg Yb targets using the 10 g and 20 g weight resin columns, respectively, were performed These separation results are shown in Fig 8 Unsuccessful separations shown in Figs 8a and 8b were experienced due to incorrect elution conditions such as the inadequate resin bed and the un-optimized eluent concentration and elution scheme The good separations shown in Figs 8c–8e confirmed our predictions, the results of which lay in the above

mentioned calculations related to the capacity factor, k’,

the separation factor, α, and the solute loading on the resin column The good separation performance and the significantly shorter elution time (from 4 to 6 hours for the 50 mg Yb loading) compared to the separations basing on the LN resin (12 hours for the 10 mg Yb

loading) reported in the References 8–11 make the

HDEHP coated OASIS-LHB resin (OASIS-E30RS)

favorable for the separation of the bulk Yb amount from

the trace quantity of Lu This capability of

OASIS-E30RS resin offers a useful way of separation of

no-carrier added 177Lu radioisotope from the larger amount

of Yb target As for the separation performance the tailing was shown from the Yb elution peak This unfavorable characteristic was assumed to be the result

of larger particle size (54.4 µm) resin.15 The tailing problem will be solved by using the OASIS-LHB resin

of smaller particle size (30 µm)

Fig 8 Elution profiles of Lu3+ and Yb 3+ ions achieved on the OASIS-E30RS resin columns of variable weights; (a) resin weight: 5 g; column: 15.9 cm length × 1.0 cm i.d; Vm = 5.7 ml eluent: 3.0M HCl, flow rate: 1.0 ml/min, solute composition: 30 mg Yb + 1 µg Lu; (b) resin weight: 10 g; column: 31.8 cm length × 1.0 cm i.d; Vm = 11.5 ml; eluent: 2.75M HCl (0–100 min); 3.0M HCl (100–250 min); flow rate: 1.3 ml/min; solute composition: 30 mg Yb + 1 µg Lu; (c) resin weight: 10 g; column: 31.8 cm length × 1.0 cm i.d; Vm = 11.5 ml; eluent: 2.75M HCl (0–80 min.); 3.0M HCl (80–150 min); 6M HCl (150–220 min); flow rate: 1.3 ml/min; solute composition: 30 mg Yb + 1 µg Lu.; (d) resin weight: 20 g; column: 28.5 cm length × 1.5 cm i.d; Vm = 23.0 ml; eluent: 2.75M HCl (0–90 min); 3.0M HCl (90–160 min); 6M HCl (160–220 min); flow rate: 2.5 ml/min; solute composition: 50 mg Yb + 1 µg Lu; (e) resin weight: 25 g; column: 35.5 cm length × 1.5 cm i.d; Vm = 28.8 ml; eluent: 2.75M HCl (0–

150 min); 3.0M HCl (150–300 min); 6M HCl (300–370 min); flow rate: 2.5 ml/min; solute composition: 50 mg Yb target+ no-carrier added 177 Lu