Sorption Characteristics and Chromatographic Separation of 90Y3+ from 90Sr2+ from Aqueous Media by Chelex-100 (Anion Ion Exchange) Packed Column

El-Shahawi, Mohammad S.; Alwael, Hassan; Alsibaai, Abdulaziz A.; Hamza, Abdelgany; Algethami, Faisal K.; Alshareef, Fatmah M.; El-Khouly, Sanaa H.; Eweda, Neven

doi:https://doi.org/10.1155/2024/6232381

International Journal of Analytical Chemistry

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Abstract Introduction Materials and Methods Results and Discussion Data Availability Ethical Approval Conflicts of Interest Acknowledgments Supplementary Materials References Copyright Related Articles

Research Article | Open Access

Volume 2024 | Article ID 6232381 | https://doi.org/10.1155/2024/6232381

Sorption Characteristics and Chromatographic Separation of ⁹⁰Y³⁺ from ⁹⁰Sr²⁺ from Aqueous Media by Chelex-100 (Anion Ion Exchange) Packed Column

Mohammad S. El-Shahawi,¹Hassan Alwael,¹Abdulaziz A. Alsibaai,¹Abdelgany Hamza,¹Faisal K. Algethami,²Fatmah M. Alshareef,¹Sanaa H. El-Khouly,³and Neven Eweda¹

Academic Editor: Mahmood Ahmed

Received13 Dec 2023

Revised29 Feb 2024

Accepted09 Apr 2024

Published13 May 2024

Abstract

There is growing demand for separation of ⁹⁰Y carrier free from ⁹⁰Sr coexisting to produce high purity ⁹⁰Y essential for radiopharmaceutical uses. Thus, in this context the sorption profiles of Y³⁺ and Sr²⁺ from aqueous solutions containing diethylenetriaminepenta acetic acid (DTPA), ethylenediaminetetra-acetic acid (EDTA), acetic acid, citric acid, or NaCl onto Chelex-100 (anion ion exchange) solid sorbent were critically studied for developing an efficient and low-cost methodology for selective separation of Y³⁺ from Sr²⁺ ions (1.0 × 10⁻⁵ M). Batch experiments displayed relative chemical extraction percentage (98 ± 5.4%) of Y³⁺ from aqueous acetic acid solution onto Chelex-100 (anion ion exchanger), whereas Sr²⁺ species showed no sorption. Hence, a selective separation of Y³⁺ from its parent ⁹⁰Sr²⁺ has been established based upon percolation of the aqueous solution of Y³⁺ and Sr²⁺ ions containing acetic acid at pH 1-2 through Chelex-100 sorbent packed column at a 2 mL min⁻¹ flow rate. Y³⁺ species were retained quantitatively while Sr²⁺ ions were not sorbed and passed through the sorbent packed column without extraction. The sorbed Y³⁺ species were then recovered from the sorbent packed column with HNO₃ (1.0 M) at a 1.0 mL min⁻¹ flow rate. A dual extraction mechanism comprising absorption associated to “weak-base anion exchanger” and “solvent extraction” of Y³⁺ as (YCl₆)³⁻ and an extra part for “surface adsorption” of Y³⁺ by the sorbent is proposed. The established method was validated by measuring the radiochemical (99.2 ± 2 1%), radionuclide purity and retardation factor ( = 10.0 ± 0.1 cm) of ⁹⁰Y³⁺ recovered in the eluate. Ultimately, the sorbent packed column also presented high stability for reusing 2-3 cycles without drop in its efficiency (±5%) towards Y³⁺ uptake and relative chemical recovery. A proposed flow sheet describing the analytical procedures for the separation of ⁹⁰Y³⁺ from ⁹⁰Sr²⁺ using chelating Chelex 100 (anion exchange) packed column is also included.

1. Introduction

In nuclear medicine, ⁹⁰Y is an important radioisotope due to its satisfactory physical characteristics that include emissions that allow tissue diffusion to a moderately extensive range, a suitable half-life ( = 64.4 h) and a nonradioactive daughter [1–6]. The United States-food and drug administration (US-FDA) has accepted Zevalin drug that incorporates ⁹⁰Y [7, 8]. So, it is essential to the ⁹⁰Sr impurity in ⁹⁰Y samples owing to the radiotoxicity of ⁹⁰Sr [9, 10]. ⁹⁰Y decays to the stable ⁹⁰Zr daughter, thus it is used as a pure β-emitter. High complex formation constants of Y³⁺ with complexing ligands make ⁹⁰Y³⁺ valued in preparing radiopharmaceutical reagents [11, 12]. In light of the perceived need to abolish the radiotoxicity risk poses by ⁹⁰ Sr, accurate separation, accurate, and reliable removal of ⁹⁰Sr impurities from Y samples is of great importance. Therefore, great attention has been oriented towards establishing selective and low cost methods for chromatographic separation of ⁹⁰Sr²⁺ from ⁹⁰Y³⁺ samples with good radiochemical and radionuclide purity.

Recently, huge volumes of radioactive wastes and a diversity of radionuclides are generated from nuclear reaction process are certainly released into the natural environment [13, 14]. Thus, many approaches have been described in the last two decades for complete separation of ⁹⁰Y³⁺ from various solutions via 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) in kerosene, [15], solvent extraction [16–20], organic resin and chelating agent and TBP-treated resins such as amberlite XAD-4 [21–24], cation ion exchanger [25, 26], pyridyl azo napthol (PAN)/zeolite composite [27], Teflon grain support di (2-ethyl hexyl) phosphoric acid-dodecane [28], Chelex-100 [29], paper chromatography [30], nafion-117, and dowex 50W X8 [31]. A ⁹⁰Y generator system contained two extraction columns and sec-octylphenoxy acetic acid and tri-n-butyl phosphate as modifier have been used for separation of ⁹⁰Y from ⁹⁰Sr [32–34]. ⁹⁰Sr/⁹⁰Y generator elutes ⁹⁰Y free from ⁹⁰Sr with relative chemical recovery over 90% [35, 36]. Inorganic ion exchangers, e.g., cerium (IV) iodotungstate [37], zirconium-vanadte gel [38, 39] and chelating Chelex-100 ion exchange [10] in several steps have been used for complete separation of ⁹⁰Y³⁺ from ⁹⁰Sr²⁺ [31–34]. However, some of these methods have many drawbacks and limitations such as complexity, high cost, the necessity for suitable operation, and preconcentration due to their low capacity. Therefore, searching for establishing low cost, simple systems with short analytical time and ruggedness for chromatographic separation of Y³⁺ from Sr²⁺ species in aqueous solutions with good radiochemical and radionuclide purity are much sought after [37, 38].

With this background in mind, taking into account the importance of highly pure ⁹⁰Y³⁺, the characteristics of the chelating group iminodiacetate moieties of the Chelex-100 anion ion exchanger and some of the synthesized inorganic sorbents as ideal and ecofriendly solid sorbents and in continuation to our previous study [10, 38–43], the current study is aimed to (i) revising the sorption profiles of Y³⁺ and Sr²⁺ onto the anion ion exchanger as a new candidate solid sorbent, (ii) establishing a simple and low cost and selective chromatographic separation of ⁹⁰Y from its parent ⁹⁰Sr by chelating Chelex-100 (anion ion exchanger) sorbent packed column and finally, and (iii) testing the reusability of the established chelating Chelex-100 sorbent packed column towards separation of Y³⁺ from its parent Sr²⁺ species in aqueous solutions. These results are supportive to recognize the analytical utility of the Chelex-100 in nuclear medicine, waste management and to properly assign the physicochemical behavior of radionuclide ⁹⁰Y³⁺ and ⁹⁰Sr²⁺.

2. Materials and Methods

2.1. Chemicals

Analytical reagents chemicals were used as received. High-density polyethylene (HDPE) bottles and all glassware’s were immersed in hot detergent for 24 h and soaked in the acid mixture of HCl (50% v/v)-conc. HNO₃ (3.0 M) at 1 : 1 v/v ratio, washed with double distilled water and finally dried in oven at 80–90°C. Stock solutions (1.0 M) of Sigma-Aldrich diethylenetriaminepenta acetic acid (DTPA), ethylenediaminetetra acetic acid (EDTA), HCl, HNO₃, acetic acid, citric acid, and NaCl were prepared in deionized water. The chelating Chelex-100 (anion exchanger) (100–200 mesh) was purchased from BDH (Poole, England) and was used after washing 3-4 times with deionized water before use. ⁸⁹Sr tracer was used as a substitute for ⁹⁰Sr and the radio tracers ⁹⁰Y³⁺ and ⁹⁰Sr²⁺ were acquired by exposing the target Y₂O₃ and SrCO₃ (99.9% purity) in Al container at an average thermal neutron flux density of 1.3 × 10¹³ neutrons/cm²/s at the ERR-1 research reactor (Atomic Energy Authority, Inshas, Egypt). Beta counting (liquid scintillation) was used to check ⁹⁰Sr²⁺ efficiency. Millipore water (resistivity 18.2 MΩcm) was used in all experiments. The test solutions were prepared by spiking 100 mL of the water sample with a certain amount of YCl₃ (1.771 × 10⁻² M) and SrCl₂ (1.323 × 10⁻² M) individually.

2.2. Apparatus

A Geiger–Muller ( Counter) and window detector and a Scaler Ratementer SR7 (γ-Scintillation Counter) were used for ordinary gamma ray counter and it is fixed with well NaI (Tl) crystal. A high purity germanium (HPGe) coupled to a calibrated multichannel gamma analyzer (Silena, Milan, Italy) was employed to test impurities in the irradiated Y₂O₃ and SrCO₃ as reported earlier [10]. The activity of ⁹⁰Sr activity was monitored as reported [10]. Standard radionuclides were prepared from a mixed source of the radioisotopes ¹⁵⁵Eu (86.5 and 105.3 keV), ⁵⁷Co (122.1 and 136.5 keV), and ¹³⁷Cs (661.6 keV). A mechanical shaker (Corporation Precision Scientific, Chicago, USA) with a shaking rate of 10–250 rpm was used for performing batch experiments. A centrifuge Chermle Z 230 A of 5500 rpm speed was also used. A close-fitting glass Jar chromatography (40 cm L and 5 cm id) of Whatmann paper No 1 (3 cm × 30 cm), Milli-Q Plus water system (Millipore, Bedford, MA, USA), and glass columns of 10.0 cm length (8, 15, and 20.0 mm internal diameter) were used in flow experiments. A digital micropipette (5.0–100 µL) and a Jenway pH meter (model 3510) were used for the preparation and measuring the pH of more diluted working solutions, respectively.

2.3. Preparation of the Radioactive ⁹⁰Y and ⁰⁹Sr Tracers

An accurate mass of SrCO₃ (200 mg, 99.9% purity, MW = 147.63) or Y₂O₃ (200 mg, 99.9% purity, MW = 225.8) was enfolded in pure Al foil precleaned with acetone and air dried before use to reserve the solid from possible contamination during cooling in the reactor. Al foil was then presented into another outer leak proof of Al and the target compound SrCO₃ and Y₂O₃ were exposed for two days in the perpendicular channel of 2 MW water-cooled research reactor ERR-1 at average thermal neutron flux density of 1.3 × 10¹³ n/cm²s (Atomic Energy, Inshas, Egypt). The exposed target was left-hand to cool for 24 h before use. Accurate masses of each exposed SrCO₃ (200 mg) and Y₂O₃ (200 mg) were dissolved in HCl (50.0 mL, 2.0 M). The test solution of ⁸⁹SrCl₂ and ⁹⁰YCl₃ was heated to dryness and redissolved in deionized water (100 mL) to achieve the final concentrations of ⁸⁹SrCl₂ (1.323 × 10⁻² M) and ⁹⁰YCl₃ (1.771 × 10⁻² M), respectively. In the irradiated product, the impurities were then checked as reported earlier [10]. The specific activity (S) was then computed as reported earlier [40–42]. The purity of irradiated ⁹⁰YCl₃ was also confirmed from the decay shape over 3 half-lives () period at neutron flux density of 1.3 × 10¹³ neutrons/cm²/s as reported [44, 45].

2.4. General Batch Extraction Procedures

In a series of precleaned penicillin bottle, accurate masses (0.100 ± 0.002 g) of the precleaned Chelex-100 (Anion ion exchanger) were transferred and equilibrated with 20.0 mL solutions containing known concentrations (1.0 × 10⁻⁵ M) of YCl₃ or SrCl₂ in acetic acid, DTPA, EDTA, citric acid, or NaCl (1.0 × 10⁻³ M). The test solutions were then shaken for 60 min at various pH at 25°C. The solid phase extractor in each solution was allowed to settle down and an accurate volume (1.0 mL) of the aqueous phase of each solution was separated out. The radioactivity of ⁹⁰Y and ⁹⁰Sr, the relative extraction percentage (%E) and the amount () of Y³⁺ and/or Sr²⁺ between the sorbent phase and the aqueous solution were then computed from their activities before and after extraction as reported [38, 39]. The distribution ratio (D, mL/g) of Y³⁺ and/or Sr²⁺ were also calculated using the following equation [43]:where V is the volume of solution (mL) and W is the mass of the dry ion exchanger (g). The quantity () of Y³⁺ extracted per unit mass of the sorbent (mol g⁻¹) was then calculated as reported earlier [39].

2.5. Separation of Y³⁺ from Sr²⁺ by Chelex-100 (Anion Exchanger) Packed Column

An accurate mass (1.0 ± 0.002 g) of the Chelex-100 (anion exchanger) sorbent was homogeneously packed in glass column (10.0 cm length × 0.8 cm i.d). An aqueous solution of acetic acid (1.0 × 10⁻³ M) of pH 1-2 was introduced into the sorbent packed column and quartz wool was then placed at the top of the resin after the sorbent had established down. This step helps in avoiding the disturbance of the resin particles during percolation of the test solution. Column was then washed with water 2-3 times at a 2.0 mL/min flow rate. The test solution (25 mL) containing Y³⁺ and Sr²⁺ and DTPA (1.0 × 10⁻³ M) was permeated to pass through the column at a 2.0 mL min⁻¹ flow rate. Y³⁺ was only sorbed quantitatively, whereas Sr²⁺ species were passed through the column without sorption as specified from the radioactivity measurement of ⁹⁰Y³⁺ and ⁹⁰Sr²⁺ in the effluent. The sorbed Y³⁺ species were then recovered from the sorbent packed column with HNO₃ (10 mL, 1.0 × 10⁻¹M) at a 2.0 mL min⁻¹ flow rate. The recovered Y³⁺ solutions were heated to dryness, redissolved in ultra-pure water, and the Y³⁺ purity was finally determined via computation of the half life () as reported [39, 44]. Moreover, the influence of other parameter such as flow rates (1.0–5 mL min⁻¹) and the internal diameter (0.8, 1.5, and 2.0 cm) on the analytical performance of Chelex-100 packed column for separation of ⁹⁰Y³⁺ from ⁹⁰Sr²⁺ was also examined.

2.6. Determination of Radiochemical and Radionuclidic Purity of ⁹⁰Y

⁹⁰Y purity was critically checked as follows: On a strip of Whatmann No. 1 paper, a drop of 5.0 µL was put on the lower end of the chromatographic paper. After the spot has dried, the strip was immersed at its lower end in TRIS buffer (0.1 M) of pH 7 as a developer using ascending chromatograph technique without reaching the spot. The paper was left for 5-6 min to develop; the solution was then reserved out and the paper was allowed to dry. The paper was divided into equal parts (1.0 cm sections) and GM was used for counting β activity and the sorption factor () was then computed. The radionuclidic purity of ⁹⁰Y³⁺ in the eluate was determined from the purification factor () = A/, where A and are the activity of ⁸⁹Sr in the eluate and solution, respectively. The radionuclidic purity was also computed from the decay curve over a period of at least 3 half-lives. The decay curve of ⁹⁰Y³⁺ was planned by detecting activity at one day intervals for 10 days after elution [46, 47].

3. Results and Discussion

3.1. Preliminary Study on the Sorption Profile of Y³⁺ and ⁸⁹Sr²⁺ onto Chelex-100

The majority of ion exchangers using organic resin and chelator/complexing agent are simple and fast for separation of elements. However, they do not offer a ready-to-use eluate [3, 5]. Introductory study on Y³⁺ and Sr²⁺ uptake from the aqueous solution by chelating Chelex-100 (anionic form) displayed significant Y³⁺ sorption in a short time. Thus, a detailed study on the sorption profile of Y³⁺ and Sr²⁺ from the aqueous solution onto the established Chelex-100 sorbent was critically studied.

3.2. Programming of the Analytical Parameters

3.2.1. Impact of pH of the Extraction Media

The pH has a significant influence on the retention capacity for the ion exchange materials since the electrostatic interactions are the driving forces. Thus, in batch experiment, the uptake of Y³⁺ and Sr²⁺ (1.0 × 10⁻⁵ M) as YCl₃ or SrCl₂ from the test aqueous solutions containing DTPA, EDTA, acetic acid, citric acid, or NaCl (1.0 × 10⁻³ M) by Chelex-100 sorbent was studied over a wide range of solution pH (pH 1–11) after a shaking period of 60 min. In the aqueous phase, the amount of Y³⁺and Sr²⁺ was then determined. The sorption data of Y³⁺ and Sr²⁺ from the various extraction media into Chelex-100 (anionic form) are summarized in Table 1. In acetic acid and DTPA media, the sorption profiles of Y³⁺ and Sr²⁺ are also illustrated in Figures 1 and 2, respectively. In acetic acid media, the K_d of Y³⁺ sorption onto Chelex-100 sorbent reached a maximum value at pH 1–6 ( = 9930.6 ± 12.4), whereas the gradually decreased on increasing the solution pH and reached minimum value ( close to zero negligible value) at pH11 as shown in Figure 1. On the other hand, Sr²⁺ uptake was insignificant in the pH range pH 1–5 ( = 0.0) and it gradually increased on growing the pH and reached maximum value at pH 9 ( = 9910.6 ± 10.6) and levelled off at higher pH up to pH 11 ( = 6000.7 ± 9.3) as shown in Figure 1. The sorption selectivity of Y³⁺ at pH 1–3 onto chelating Chelex-100 sorbent in the various extraction media followed the order: NaCl ( = 12278.5 ± 13.8 > acetic acid ( = 9930.6 ± 12.4) > EDTA ( = 9905.3 ± 5.4) > citric acid ( = 9886.4 ± 5.8) > DTPA ( = 7004.7 ± 3.3). At pH 1–3, Sr²⁺ species did not retained except in NaCl, where = 66654.6 ± 5.7 (Table 1).

In DTPA or acetic acid media of pH ranging from pH 1 to pH 4, Y³⁺ species were retained quantitatively onto the chelating Chelex-100 ion exchanger sorbent and the values of were reproducible compared to EDTA, citric acid, or NaCl. Representative plot of versus of pH of Y³⁺ and Sr²⁺ sorption onto Chelex-100 (anion ion exchanger) from aqueous DTPA solution (1.0 × 10⁻³ M) after 60 min shaking time at 25 ± 0.1°C is shown in Figure 2. The observed behavior in Figure 2 is most likely attributed to the possible formation of nonpolar complex species of Y³⁺ species (YCl₆)³⁻ with the available iminodiacetate moieties of the chelating Chelex 100 sorbent at pH ≤ 3 (pK_a1 = 3.2) [40, 42, 43]. At low pH (pH ≤ 3), the possible interaction between the formed complex anion of yttrium (YCl₆)³⁻ and the protonated iminodiacteate moieties of the chelating Chelex−100 anion ion exchanger by forming ternary complex ion associate may also contributed in the observed trend at low pH ≤ 3 [42, 43]. On the other hand, at pH above pH 3, one of the two carboxylic acids of the iminodiacetate moiety is deprotonated carrying a negative charge which attracts other positive cation present in extraction media, e.g., Na⁺ (introduced from pH adjustment by diluted NaOH which compete effectively with Y³⁺ because of their considerably higher concentration in solution [42]. The fact that, in acidic solutions, the N atom of the iminodiactic group retaining free electron pair is protonated, hence the resin is most likely can acts as weakly basic anion exchanger [43]. In addition, deprotonation of the second carboxylic group of the iminodiacetic moieties could also be proceeded at pH > 7, resulting in destabilization of the “guest-host” complexes between Y³⁺ and aminocarboxylic moieties [43]. This exchanger is also commonly regarded as an amphoteric ion exchanger and its ion exchange function depends on the solution pH that in contact with the resin as presented in Scheme 1.

In DTPA, EDTA, acetic acid, citric acid, or NaCl medium at pH > 7, Chelex-100 sorbent displayed good retention towards Sr²⁺ and the extraction profile of Sr²⁺ followed the order: NaCl ( = 12276.9 ± 5.7> citric acid ( = 9759.6 ± 5.7) > acetic acid ( = 7212.2 ± 5.8) > EDTA ( = 3623.4 ± 3.7) > DTPA ( = 1614.5 ± 5.2) was achieved. On the other hand, at pH > 7, the chelating Chelex-100 sorbent displayed no affinity towards Y³⁺ from citric acid, EDTA or DTPA. The fact that the chelating agents EDTA and DTPA act as competitors having similar groups with the Chelex-100 sorbent and both are able to form complexes in solution with Y³⁺ and Sr²⁺ preventing their adsorption while acetic acid is the weakest medium [42, 48]. This behavior is most likely attributed to the strong and weak ion-association interaction of the accessible specific active sites of the Chelex-100 solid extractor towards Sr²⁺ and Y³⁺, respectively, as reported the authors in [42, 48]. On the other hand, it may be thought that for smaller molecules a more pronounced difference between the adsorption sites on the surface of Chelex-100 and inside the sorbent pores as reported [48]. In acetic acid, EDTA or NaCl at pH > 7, separation of Y³⁺ from Sr²⁺ was not complete. Thus, in Y³⁺ separation from Sr²⁺, acetic acid, or DTPA (1.0 × 10⁻³ M) was implemented as a preferred extraction medium at lower pH in the subsequent study.

3.2.2. Impact of Shaking Time

The influence of shaking time over 0.0–2.0 h on Y³⁺ uptake from aqueous acetic acid or DTPA solution (1.0 × 10⁻³ M) onto Chelex-100 was studied. Y³⁺ sorption onto the ion exchanger was fast at the initial stage and attained maximum sorption percentage after 60 min shaking time and remained constant at extra time. This trend was supported from the value of half life () of Y³⁺ retention via the plots of log of Y³⁺ versus shaking time. The value of the half-life () of Y³⁺ retention from the aqueous acetic acid or DTPA solution as computed from the plot of log of Y³⁺ versus shaking time was in the range 2.42 ± 0.05 min. Representative plot is given in the Supplementary Description (SD. 1). Thus, the rate-controlling step for Y³⁺ sorption by the sorbent is not only gel diffusion control as in the ion exchangers [49, 50]. At the initial stage of shaking time, the plot of %E of Y³⁺ versus log time was fast and linear approving the occurrence of intraparticle diffusion [10, 50]. Thus, a 60 min shaking time was adopted in the following study.

3.2.3. Influence of Media Polarity

The extraction medium in solid phase extraction procedures has a pronounced effect on the performance of Y³⁺ separation. Thus, Y³⁺ and Sr²⁺ ions uptake from the test aqueous solutions (20.0 mL) containing various known concentrations (1 × 10⁻⁵–1.0 M) of HCl or HNO₃ at standard concentration of Y³⁺ and Sr²⁺ (1.0 × 10⁻⁵ M) was studied over a shaking time of 60 min at room temperature. At equilibrium, the remained Y³⁺ and Sr²⁺ ions in the aqueous phase was measured and the extraction percentage (E, %) and the D were then computed as reported [10]. In HCl media, the data are presented in Figure 3, where the E% and D of Y³⁺ and Sr²⁺ by the sorbent decreased on rising HCl concentration from 1.0 × 10⁻⁵ to 1.0 M. At HCl concentration ≥1.0 × 10⁻¹ M, Sr²⁺ species were not retained, while 75.0 ± 2.1% of Y³⁺ was retained. The strong interaction of the active sites of the sorbent with Y³⁺ may account for this trend [51, 52]. The strong binding of Y³⁺ to form [YCl₆]³⁻ complex species [53] compared to Sr²⁺ in HCl media may also account for the observed trend. In HNO₃ (1.0 × 10⁻⁵–1.0 M), Y³⁺ species did not sorbed onto chelating Chelex-100 sorbent whereas significant sorption of Sr²⁺ ( = 650.4 ± 3.64 mL g⁻¹) was noticed at 1.0 × 10⁻⁵ M and decreased on rising HNO₃ concentration up to 1.0 M ( = 210.2 ± 3.64 mL g⁻¹). The average chemical extraction percentage of ⁸⁹Sr and ⁹⁰Y from acetic acid (1.0 × 10⁻³ M) at different solution pH onto Chelex-100 was also studied. The results are illustrated in Figure 1 where in acetic acid media at pH ≤ 5, Y³⁺ species were retained quantitatively while Sr²⁺ ions did not get sorbed. However, in the subsequent study, HNO₃ (1.0 × 10⁻¹ M) was nominated as a prober reagent for Y³⁺recovery from Chelex-100 sorbent packed column since it is easily evaporated by gentle heating.

3.3. Possible sorption Mechanism for Y³⁺ Retention

The affinity of the sorbent towards Y³⁺ played an important role on its uptake. The nature and number of the specific sorbent sites are involved instantaneously in Y³⁺ uptake from the solution [16]. The chelating Chelex-100 sorbent acts as an active “weak anion-exchanger” towards complex species of Y³⁺ such as (YCl₆)³⁻ in HCl media [53] and “liquid-liquid extraction” with the salt performing as salting-out reagent in Y³⁺ uptake. The salt added decreases the water molecules available to solvate Y³⁺ ions which would be required out of the solvent onto the sorbent phase. Thus, water structure enforced ion pairing is somewhat the driving force for Y³⁺ uptake and “surface adsorption” effectively take part in the Y³⁺ extraction [53, 54]. Based on the obtainable results and the data reported earlier [54, 55], a dual sorption mechanism involving absorption related to “weak-base anion exchange” and “solvent extraction” in addition to “surface adsorption” of Y³⁺ is proposed. Thus, retention mechanism of Y³⁺ can be stated by the following equation [54, 55]:where and are the equilibrium concentrations of Y³⁺ ions onto the sorbent and in solution, respectively. and are the equilibrium concentrations of Y³⁺ absorbed and adsorbed onto the sorbent while S and are the parameters of the Langmuir adsorption model [54, 55].

3.4. Separation of ⁹⁰Y³⁺from Sr²⁺ by Sorbent Chelex-100 (Anion Form) Packed Column

An aqueous solution (25.0 mL) composed of acetic acid (1.0 × 10⁻³ M), Y³⁺ and Sr²⁺ ions (1.0 × 10⁻⁵ M) was permeated through Chelex-100(Anion exchanger) packed column at a reasonable flow rate (2.0 mL min⁻¹). Y³⁺ species were retained quantitatively whereas Sr²⁺ ions were passed without uptake as revealed from ICP-OES determination of ⁹⁰Y³⁺ and ⁹⁰Sr²⁺ ions in the effluent versus reagent blank. Selection of proper eluting agent prior to use of ⁹⁰Y³⁺ for labeling and radiolysis of organic support materials is crucial and is identified as the main limitations of current 90Sr/90Y [35, 56]. Thus, the established methodology offered a facile, better selectivity and simple approach compared to the published work [12–21, 57]. Numerous eluting agents such as HNO₃, HClO₄, H₂SO₄, and acetic acid (1.0 × 10⁻¹M) were checked for recovery of Y³⁺ from chelated Chelex-1000 packed column. Among these reagents, good percentage recovery (99.5 ± 2.9%) of ⁹⁰Y³⁺ was only achieved with HNO₃ (10 mL, 1.0 × 10⁻¹ M) as a prober agent for Y³⁺ recovery at a 1.0 mL/min flow rate using Chelex-100 sorbent packed glass column of 8 mm internal diameter. On the other hand, HNO₃ can easily remove from the recovered ⁹⁰Y³⁺ solution by gentle evaporation. The solid residue was redissolved in deionized water and analyzed as reported [56].

Moreover, the impact of the internal column diameter (0.8, 1.5, and 2.0 cm) on the performance of chelated Chelex-100 packed column on the separation of Y³⁺ from Sr²⁺ ions was examined at a 1.0 mL min⁻¹ flow rate. Acceptable separation and relative chemical recovery of Y³⁺ from Sr²⁺ was only achieved at 8 mm internal diameter of the column, whereas at internal diameter greater than 8 mm, Y³⁺ recovery was not complete (<90%) The influence of the flow rate (1.0–5 mL min⁻¹) on Y³⁺ separation from ⁹Sr²⁺ ions was critically tested. Good separation with acceptable relative chemical recovery (over 99%) of Y³⁺ from Sr²⁺ ions was achieved at a flow rate of 1.0 mL min⁻¹. Thus, in the subsequent study, the flow rate and the internal diameter of the Chelex −100 sorbent packed column were adopted at a 1.0 mL min⁻¹ flow rate and 8 mm internal diameter.

3.5. Radiochemical Purity of ⁹⁰Y³⁺

Validation of Chelex-100 (anion form)-packed column for chromatographic separation of ⁹⁰Y from ⁹⁰Sr was critically tested by calculating the retardation factor () from the radio chromatogram of ⁹⁰Y on the original spot constructed by plotting radioactivity (cpm) versus travelled distance, cm. The data are presented in Figure 4 and the value was 10.0 ± 0.1 cm of total activity on the original spot in agreement with the data published earlier [31–36]. These data also signify that over 99.2 ± 2.1% of ⁹⁰Y³⁺ species are present in the eluate as ⁹⁰YCl₃ as reported by the authors in [46, 56].

3.6. Radionuclides Purity of ⁹⁰Y³⁺

The proposed protocol was tested by measuring the radionuclidic purity using the purification factor (), where A and are the ⁹⁰Sr²⁺ activity in the recovered and loaded solution, respectively. The value was lower than 1.1 × 10⁻⁶, demonstrating negligible impurity of ⁹⁰Sr²⁺ in ⁹⁰Y³⁺ solution [45, 46]. The radionuclidic purity of ⁹⁰Y³⁺ was also computed from radioactivity (cpm) plot of ⁹⁰Y³⁺ in solution versus time (day) (Figure 5). The value of half life (t_1/2) of ⁹⁰Y as computed from the decay curve (Figure 5) was found equal 64.4 h in good agreement with the data reported earlier [38, 39], revealing high purity of ⁹⁰Y³⁺ with good performance of Chelex-100-packed column towards ⁹⁰Y³⁺ separation from ⁹⁰Sr²⁺. The whole analytical procedures for ⁹⁰Y³⁺ separation from ⁹⁰Sr²⁺ by Chelex−100 sorbent is presented in the proposed flowsheet (Figure 6).

4. Conclusion, Drawbacks, and Future Outlooks

In summary, the current study presented an optimized protocol for selective separation of ⁹⁰Y³⁺ from ⁹⁰Sr²⁺ with good purity using chelating Chelex-100 (anion exchanger) packed column. The membrane-like structures and the available active sites of the Chelex-100 solid extractor permit good separation of Y³⁺ from Sr²⁺ compared to other sorbents [12–22, 57]. Compared to previous methods for separation of ⁹⁰Y³⁺ from ⁹⁰Sr, Chelex-100 requires slight sample operation to reduce the analysis time, and it does not require solvent evaporations and reconstruction step. This method displays high selectivity for separation of ⁹⁰Y³⁺ from ⁹⁰Sr²⁺ at the low level. The purity of ⁹⁰Y can be tested by quality control procedures. The established extractor looks low cost and valuable alternative sorbent over the common rigid or granular solid extractors. A dual sorption mechanism of Y³⁺ comprising both “surface adsorption” and an added component of “ion exchanger and/or solvent extraction” is anticipated. In addition, the results revealed the possible use of Chelex-100 sorbent packed column for complete enrichment and recovery of Y³⁺ for 2-3 times without significant decrease in its performance. Work is ongoing for studying the impact of memory effect, various organic materials in water samples and online enrichment of ultratrace levels of Y³⁺ from great volume of water samples followed by subsequent determination. The study also shows that the established extractor can be used as cheap, efficient and ecofriendly solid sorbent for Y³⁺ separation from Sr²⁺, whereas other methodologies have high operational costs and sometimes yield undesirable by-products when linked to physical and chemical methods. The fact that the use of one factor at a time has many drawbacks and shortcomings and the cooperating results of numerous features might advance the signal and the utility of the proposed methodology. Therefore, design experiment for separation of Y³⁺ from Sr²⁺ is suggested in the forthcoming study. The developed strategy provides new sorbents for establishing a method for radiochemical separation.

Data Availability

The data used to support the findings of this study are included within the manuscript and supplementary materials and also from corresponding author upon request.

Ethical Approval

This article does not require IRB/IACUC approval because there were no human or animal participants.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

This project was funded by the Deanship of Scientific Research (DSR) at the King Abdulaziz University, Jeddah, Saudi Arabia, under grant no. G-476-130-1433. The authors therefore acknowledge the support by DSR for technical and financial support.

Supplementary Materials

SD. 1: rate of Y³⁺uptake from aqueous DTPA (1.0 × 10⁻³ M) solution using Chelex-100 sorbent. (Supplementary Materials)

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