# Investigation of chromatographic procedures for the analysis of cationic impurities in uranium and plutonium matrices by ICP-OES and ICP-MS

Marion Hernandez, Alexandre Quemet, Laure Montreuil, Christophe Maillard, Sarah Baghdadi

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Marion Hernandez, Alexandre Quemet, Laure Montreuil, Christophe Maillard, Sarah Baghdadi. Investigation of chromatographic procedures for the analysis of cationic impurities in uranium and plutonium matrices by ICP-OES and ICP-MS. Spectrochimica Acta Part B: Atomic Spectroscopy, 2025, 225, pp.107136. 10.1016/j.sab.2025.107136. cea-05022930

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# Investigation of chromatographic procedures for the analysis of cationic impurities in uranium and plutonium matrices by ICP-OES and ICP-MS

Marion Hernandez, Alexandre Quemet *, Laure Montreuil, Christophe Maillard, Sarah Baghdadi

CEA, DES, ISEC, DMRC, Univ Montpellier, Marcoule, France

## ARTICLE INFO

**Keywords:**

Impurities analysis
Uranium
Plutonium
ICP-MS
ICP-OES
Chromatography
Separation

## ABSTRACT

Four different separation protocols were tested to analyze several cations in a U-Pu matrix by inductively coupled plasma - optical emission spectrometry (ICP-OES) or mass spectrometry (ICP-MS): UTEVA resin with HNO₃ eluent, UTEVA resin with HNO₃/H₂C₂O₄ eluent, UTEVA resin with HNO₃/H₂O₂ eluent and TEVA resin with HNO₃ eluent. It was shown that none of the twenty nine tested cations (Al, Ag, B, Ca, Cd, Ce, Cr, Cu, Fe, Ga, La, Mg, Mn, Mo, Na, Nd, Ni, Pb, Pd, Rh, Sb, Se, Si, Sn, Sr, Ti, V, Y and Zn) was retained onto the resin, with recovery yields between 80 and 120 %. Meanwhile, the U-Pu matrix was retained onto the resin and was eliminated from the fraction containing the cations. After initial testing, two of the protocols were chosen: UTEVA resin with HNO₃/H₂C₂O₄ eluent and UTEVA resin with HNO₃/H₂O₂ eluent thanks to their efficacy and practicality. Then, the two selected protocols were applied to a uranium oxide certified reference material to validate them. Twenty three out of the thirty one impurities presents in the material (Ag, Ba, Be, Bi, Cd, Co, Cr, Cu, Dy, Eu, Fe, Gd, In, Li, Mo, Ni, Pb, Sm, Sn, Ti, V, W and Zr) were determined with good recoveries. Th was fixed onto the resin. Based on these results, it seems possible to analyze the forty one impurities in a U-Pu material by optimizing the operating conditions. These two protocols were used to study the presence of impurities in a Pu-based material to ensure the purity of the materials. Detection limits in the order of µg g⁻¹ powder were obtained.

## 1. Introduction

Throughout the nuclear fuel cycle, from mining to reprocessing, uranium undergoes several chemical, physical and isotopic trans- formations. The production of plutonium, a by-product of the nuclear reaction occurring in uranium fuel, is an integral aspect of the spent fuel reprocessing process. It is extracted from used fuels recycled as (U,Pu)O₂ mixed oxide (MOX) fuel. At each processing and reprocessing step, im- purities can be introduced. They can affect the material properties such as neutron flux during the chain reaction and phase transition temper- ature [1]. Ensuring the concentration in metal impurities in the uranium and plutonium matrices is necessary for material conformity to the nu- clear grade specifications. Thus, trace elemental analysis is important to characterize and certify materials, such as pellet before irradiation [2].

Cations analysis in uranium and plutonium matrices are commonly performed using spectrometric methods such as inductively coupled plasma – optical emission spectrometry (ICP-OES) and mass spectro- metric methods such inductively coupled plasma – mass spectrometry

(ICP-MS) [3–8]. Each of these methods has its own advantages, limita- tions and type of interferences (i.e. spectral interferences for the ICP-OES or isobaric interferences for ICP-MS). The key point for the selection of ICP-MS (for concentration of ppb or lower level) and ICP-OES (for concentration of ppm or more high level) is the concentrations of the target elements. MS offers better detection limits, but there could be isobaric and polyatomic as well as double-charge ions interferences due to the elements present and plasma gas used. Using argon as a plasma gas at ambient pressure makes it difficult to analyze certain isotopes such as ⁴⁰Ca, ⁵⁶Fe and ²⁸Si, which are mainly interfered by ⁴⁰Ar, ⁴⁰Ar¹⁶O and ¹⁴N₂, respectively. Impurities measurement at trace or ultra-trace levels in the presence of uranium or plutonium at several g L⁻¹ levels is very challenging due to space charge effects: light ions are more un- focused than heavy ions [9]. Its effect result in a suppression of analyte signals with light masses by uranium and plutonium. Although the detection limits of ICP-OES are higher than those of ICP-MS, they remain satisfactory for the analysis of impurities. However, the presence of el- ements with a rich emission spectrum, such as uranium and plutonium,

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: alexandre.quemet@cea.fr (A. Quemet).</footnote>
makes the determination of trace impurities by ICP-OES challenging due to spectral interferences [10,11].

Indeed, analyzing cations at trace and ultra-trace levels becomes difficult when a sample is concentrated over 200 mg L⁻¹ of uranium and/or plutonium (U-Pu). Matrix effects are generally reduced by sample dilution, resulting in an increase of the detection limit.

To determine elemental concentrations at µg g⁻¹ levels in U-Pu matrices, the detection limit has to be as low as possible. Such specifications can only be achieved by separating cations from the U-Pu matrix to analyze them separately. Several techniques have been developed to separate different elements from actinides prior to their determination, including precipitation, solvent extraction or chromatography [2,12–14]. Chemical precipitation and solvent extraction are time-consuming and involves using costly solvent. It generates a big volume of effluents, also.

Chromatographic separation is a method offering selectivity, ease, and speedy implementation, while also ensuring reliability. TEVA (TEtraValent Actinides) and UTEVA (Uranium and TEtraValent Actinides) resins are well known for their abilities to retain actinides [15–18]. TEVA resin, contains an aliphatic quaternary amine, having an extracting role of tetravalent actinide ions and Tc over a wide range of nitric acid concentrations [19]. UTEVA resin, made of dipentyl pentylphosphonate, extracts tetravalent actinides and hexavalent uranium as nitrato complex. The nitrate concentrations impacts the formation of nitrato complexes and therefore the actinides retention [15]. An important point is these two resins only retain tetravalent actinides (i.e. Th, Np and Pu) and uranium in HNO₃ media. Elements with another valence than +IV (except for U) are not retained onto the resin. TEVA and UTEVA are routinely used in the laboratory to separate Am, U and Pu [20,21]. In this study, a single-column separation system was used with either TEVA or UTEVA resin to retain uranium and plutonium and let through cations. Using a nitric and hydrofluoric acids mixture as conditioning, feeding and/or scrubbing phases has been reported in several studies [7,14]. It has been proven efficient to separate cations from uranium. However, fluoride ions lead plutonium to its trivalent state, which can no longer be fixed onto the resins. To fix the whole plutonium onto the resin, hydrofluoric acid must be avoided. Concentrated nitric acid, 8 mol L⁻¹, was proven to be enough to separate cations impurities from uranium using UTEVA resin [22,23]. The ATSM standard test method describes a method for quantifying 25 elements in a Pu-based material [24]. In this standard test method, Pu-based material is dissolved and converted into a 8 mol L⁻¹ HNO₃ solution prior to its separation on an AG MP-1 resin. The AG MP-1 resin is made of a quaternary ammonium, like the TEVA resin. After loading the column with the 8 mol L⁻¹ HNO₃ sample solution, the column was scrubbed with a 8 mol L⁻¹ HNO₃/0.006 mol L⁻¹ HF acid mixture.

This paper presents separation protocols developed to collect cations and U-Pu separately for routine laboratory use using TEVA or UTEVA resins, combining ICP-OES and ICP-MS. The results obtained on a certified reference material (CRM) will be discussed in terms of detection limit and recovery.

## 2. Experimental

### 2.1. Materials and reagents

Nitric acid (w = 68 %, VWR, USA) was Normapur reagent grade. The various nitric acid concentrations were obtained by diluting it with 18.2 MΩ cm deionized water produced by Millipore water purification system. Oxalic acid powder (purity >99.999 %) and hydrogen peroxide solution concentrated at 30 % were purchased from Sigma Aldrich. Hydrofluoric acid (w = 40 %, Merck, Germany) was Supapur grade.

Four multi-element solutions were prepared by mixing single element ICP standards from Perkin Elmer (USA) at 1.000 ± 0.005 g L⁻¹ for separation procedure development. A first solution, hereafter referred to as “multi14c”, contains 14 cations (Al, B, Ca, Cd, Cr, Cu, Fe,

Ga, Mn, Mo, Ni, Pb, Si and Zn) with a concentration of 62.5 mg L⁻¹ individually. A second solution, hereafter referred to as “multi20c”, contains 20 cations (Al, Ag, B, Ca, Cd, Cr, Cu, Fe, Ga, Mg, Mn, Mo, Na, Ni, Pb, Si, Sn, Ti, V and Zn) at 32.5 mg L⁻¹ individually. A third solution, hereafter referred to as “multi9c”, contains 9 cations (Ce, La, Nd, Pd, Rh, Sb, Se, Sr and Y) at 50 mg L⁻¹ individually. A fourth solution, hereafter referred to as “multi14c/U-Pu”, containing 14 cations (Al, B, Ca, Cd, Cr, Cu, Fe, Ga, Mn, Mo, Ni, Pb, Si and Zn) at 50 mg L⁻¹ individually was prepared in a U-Pu matrix [U] = 40.5 g L⁻¹ and [Pu] = 0.426 g L⁻¹. U and Pu standard solution was a EQRAIN U-Pu solution with [U] = 106.52 ± 0.13 g kg⁻¹ and a MP2 reference material with [Pu] = 1.1192 ± 0.0013 g kg⁻¹ provided by the Analytical Methods Committee (CETAMA) of the French Alternative Energy and Atomic Energy Commission (CEA). These lists of cations were selected for the needs of different programs carried out on the facility.

A CRM called Morille supplied by the CETAMA was used to validate the separation procedures [14,25]. It is made up of spiked U₃O₈ powder in which 29 elements concentrations are certified and 2 are indicators. The CRM was dried at 100 °C for 8 h in a drying oven. The dissolution was performed using the routine procedure used in the laboratory for U-Pu oxide powder. About 100 mg was dissolved in a 5 mL (8 mol L⁻¹ HNO₃/0.05 mol L⁻¹ HF) acid mixture to simulate U-Pu powder dissolution [20,26]. Three independent dissolutions were performed.

All dilutions were performed volumetrically using pre-calibrated micropipettes.

A single chromatography column system was used for uranium and plutonium extraction. 2 mL TEVA and UTEVA prepacked resins (Triskem, France) with 100–150 µm particle size were used in gravity mode according to different separation procedure. The flow-rate was approximatively 25 mL h⁻¹ (v = 50 cm h⁻¹).

### 2.2. Instrumentation

Trace cations analyses by ICP-OES were performed using two Optima 8300 DV (Perkin Elmer, USA). In the absence of U-Pu, an Optima ICP-OES set up on a lab bench was used to analyze the solutions with greater speed and ease. For radionuclides analysis, an Optima 8300 DV (Perkin Elmer, USA) nuclearized in a glove box was used. The glove box holds the introduction system and an autosampler. Both instruments were equipped with a micro-nebulizer and a small volume gutter cyclonic nebulization chamber. Sc (5 mg L⁻¹) was used as internal standard for ICP-OES measurements. It helps monitoring matrices effects but no correction was applied.

For ICP-MS determination, an Elan DRCe (Perkin Elmer, USA) nuclearized in a glove box was used to operate in a radioactive environment. The glove box holds the introduction system and the autosampler. Samples were introduced into argon plasma through a Meinhard concentric nebulizer and a small volume baffled cyclonic spray chamber. An ASX-260 autosampler was used. The sample size is 3 mL minimum. ⁴⁵Sc, ¹³⁹La and ²⁰⁵Tl (1 µg L⁻¹) were used as ICP-MS internal standards. Corrections were applied (i.e. corrected intensity = measured intensity / internal standard intensity).

Single elements standards diluted in 0.5 mol L⁻¹ HNO₃ were used to prepare an external calibration curve of both spectrometric techniques. Calibration curves accuracy was checked using control solutions prepared independently. Indium is interfered at mass 113 and 115 by ¹¹³Cd and ¹¹⁵Sn, respectively. As the isotope composition is natural, isobaric interference corrections were used to quantify properly In [27].

The main operating parameters are summarized in Table 1. The wavelength and masses monitored for trace element quantification are shown in the supplementary information.

### 2.3. Separation procedures

Four different separation procedures, selected for their efficiency in fixing U and Pu, were tested. They aim at fixing U and Pu onto the resin
<table><caption>**Table 1**

ICP-OES and ICP-MS operating parameters.</caption><thead><tr><th>Instrument</th><th>ICP-OES</th><th>ICP-MS</th></tr></thead><tbody><tr><td>Plasma power</td><td>1300 W</td><td>1400 W</td></tr><tr><td>Cooling gas flow rate</td><td>15 L min<sup>-1</sup></td><td>17 L min<sup>-1</sup></td></tr><tr><td>Outer gas flow rate</td><td>0.2 L min<sup>-1</sup></td><td>1 L min<sup>-1</sup></td></tr><tr><td>Nebulizer gas flow rate</td><td>0.6 L min<sup>-1</sup></td><td>0.97 L min<sup>-1</sup></td></tr><tr><td>Solution uptake rate</td><td>1 mL min<sup>-1</sup></td><td>-</td></tr><tr><td>View mode</td><td>Axial / Radial</td><td>-</td></tr><tr><td>Acquisition time</td><td>-</td><td>3 s per isotope</td></tr></tbody></table>

and to elute the cations. All parameters are given in Table 2. The volume of sample loaded on the resin was determined so the mass of U-Pu passed on the column does not exceed 30 % of the column capacity.

### 2.3.1. Protocol A – UTEVA – HNO₃

After conditioning the column with 5 mL of 2 mol L⁻¹ HNO₃, 1.9 mL of the sample solution adjusted at 1.4 mol L⁻¹ HNO₃ concentration were loaded onto the column. The column was scrubbed once with 4 mL of 4 mol L⁻¹ HNO₃/0.1 mol L⁻¹ H₂C₂O₄ and then with 4 mL of 2 mol L⁻¹ HNO₃. Feeding and scrubbing fractions, which contain cations, were collected and reunited to be analyzed. For analysis, HNO₃ concentration was adjusted at 0.5 mol L⁻¹ by diluting the sample with deionized water. Total sample dilution factor is 132.

### 2.3.2. Protocol B – UTEVA – HNO₃/H₂C₂O₄

After conditioning the column with 4.5 mL of a mixture of 4 mol L⁻¹ HNO₃/0.1 mol L⁻¹ H₂C₂O₄, 4.5 mL of the sample solution adjusted at 4 mol L⁻¹ HNO₃/0.1 mol L⁻¹ H₂C₂O₄ were loaded onto the column. The column was scrubbed once with 6.5 mL of 4 mol L⁻¹ HNO₃/0.1 mol L⁻¹ H₂C₂O₄ mixture. Feeding and scrubbing fractions containing cations were collected and reunited to be analyzed. For analysis, HNO₃ concentration was adjusted at 0.5 mol L⁻¹ by diluting the sample with deionized water. Total sample dilution factor is 195.

### 2.3.3. Protocol C – UTEVA – HNO₃/H₂O₂

After conditioning the column with 4.5 mL of 6 mol L⁻¹ HNO₃/0.1 mol L⁻¹ H₂O₂, 1 mL of the sample solution adjusted at 6 mol L⁻¹ HNO₃/0.1 mol L⁻¹ H₂O₂ was loaded onto the column. The column was scrubbed once with 4.5 mL of 6 mol L⁻¹ HNO₃/0.1 mol L⁻¹ H₂O₂. Feeding and scrubbing fractions containing cations were collected and reunited to be analyzed. For analysis, HNO₃ concentration was adjusted

<table><caption>**Table 2**

Separation protocols procedures.</caption><thead><tr><th>Protocol</th><th>Reagent</th><th>Volume (mL)</th></tr></thead><tbody><tr><td>A. UTEVA - HNO<sub>3</sub></td><td></td><td></td></tr><tr><td>Conditioning</td><td>2 mol L<sup>-1</sup> HNO<sub>3</sub></td><td>5</td></tr><tr><td>Sample loading</td><td>1.4 mol L<sup>-1</sup> HNO<sub>3</sub></td><td>1.9</td></tr><tr><td>First scrubbing</td><td>4 mol L<sup>-1</sup> HNO<sub>3</sub> + 0.1 mol L<sup>-1</sup></td><td>4</td></tr><tr><td>Second scrubbing</td><td>H<sub>2</sub>C<sub>2</sub>O<sub>4</sub></td><td>4</td></tr><tr><td>B. UTEVA - HNO<sub>3</sub>/H<sub>2</sub>C<sub>2</sub>O<sub>4</sub></td><td>3 mol L<sup>-1</sup> HNO<sub>3</sub></td><td>4</td></tr><tr><td>Conditioning</td><td>4 mol L<sup>-1</sup> HNO<sub>3</sub> + 0.1 mol L<sup>-1</sup></td><td>5</td></tr><tr><td>Sample loading</td><td>H<sub>2</sub>C<sub>2</sub>O<sub>4</sub></td><td>4.5</td></tr><tr><td>Scrubbing</td><td>4 mol L<sup>-1</sup> HNO<sub>3</sub> + 0.1 mol L<sup>-1</sup></td><td>6.5</td></tr><tr><td>C. UTEVA - HNO<sub>3</sub>/H<sub>2</sub>O<sub>2</sub></td><td></td><td></td></tr><tr><td>Conditioning</td><td>6 mol L<sup>-1</sup> HNO<sub>3</sub> + 0.1 mol L<sup>-1</sup> H<sub>2</sub>O<sub>2</sub></td><td>4.5</td></tr><tr><td>Sample loading</td><td>6 mol L<sup>-1</sup> HNO<sub>3</sub> + 0.1 mol L<sup>-1</sup> H<sub>2</sub>O<sub>2</sub></td><td>1</td></tr><tr><td>Scrubbing</td><td>6 mol L<sup>-1</sup> HNO<sub>3</sub> + 0.1 mol L<sup>-1</sup> H<sub>2</sub>O<sub>2</sub></td><td>4.5</td></tr><tr><td>D. UTEVA - HNO<sub>3</sub></td><td></td><td></td></tr><tr><td>Conditioning</td><td>8 mol L<sup>-1</sup> HNO<sub>3</sub></td><td>4.5</td></tr><tr><td>Sample loading</td><td>6 mol L<sup>-1</sup> HNO<sub>3</sub></td><td>1</td></tr><tr><td>Scrubbing</td><td>8 mol L<sup>-1</sup> HNO<sub>3</sub></td><td>4.5</td></tr></tbody></table>

at 0.5 mol L⁻¹ by diluting the sample with deionized water. Total sample dilution factor is 147.

### 2.3.4. Protocol D – TEVA – HNO₃

After preparing the TEVA column with 4.5 mL of 8 mol L⁻¹ HNO₃, 1 mL of sample solution adjusted at 6 mol L⁻¹ HNO₃ concentration was loaded onto the resin. Then the column was scrubbed with 4.5 mL of a 8 mol L⁻¹ HNO₃ solution. Feeding and scrubbing fractions containing cations were collected and reunited to be analyzed. For analysis, HNO₃ concentration was adjusted at 0.5 mol L⁻¹ by diluting the sample with deionized water. Total sample dilution factor is 196.

## 2.4. Separation tests

The first tests helped ensuring the cations were not retained on the resin using the four protocols. Separation tests were performed on the multi14c solution (i.e. 14 specific cations without U-Pu) according to protocols A, B, C and D to select the most promising protocols. Chemical blanks were also prepared for each separation protocol: it consists of performing a separation using 0.5 mol L⁻¹ HNO₃ as a feeding solution instead of multi-elemental solution to demonstrate the absence of the 14 cations in the reactants and resin. A separation using the multi20c and multi9c solutions was performed according to protocols B and C. To assess separations repeatability, all experiments were reproduced 3 times. All the measurements were done on an ICP-OES.

Then, the protocols B and C were used to separate 14 cations in presence of U-Pu (multi14c/U-Pu solution). Protocols B and C were also applied to the EQRAIN U-Pu solution to ensure the solutions were free of cations. To assess the separations repeatability, all experiments were reproduced 3 times. All the measurements were performed using an ICP-OES.

Finally, protocols B and C were validated using the Morille CRM. After separation, the elution fractions containing the cations were analyzed by ICP-MS to measure Ag, B, Ba, Be, Bi, Cd, Co, Cr, Cu, Dy, Eu, Gd, In, Li, Mg, Mn, Mo, Ni, Pb, Sm, Sn, Th, Ti, V, W, Zn and Zr. Al, Ca, Fe and Si were analyzed by ICP-OES due to interferences when using ICP-MS such as ⁴⁰Ca⁺/⁴⁰Ar⁺ and ⁵⁶Fe⁺/⁴⁰Ar¹⁶O⁺.

The three dissolution solutions of the Morille CRM were also analyzed by the sample dilution method. The dilution of the dissolution solutions were optimized to reduce uranium concentration at 100 mg L⁻¹. Dilution factor is 180. Solutions used in calibration curve were made in a U matrix ([U] = 100 mg L⁻¹). After dilution, the cations contained in the dissolution solutions have a concentration from 0.03 to 20 µg L⁻¹.

## 2.5. Results evaluation

The cations separation performances were estimated using the recovery yields (Eq. (1)).

$$ \text{Recovery (\%)} = \frac{[\text{cation}]_{\text{after separation}}}{[\text{cation}]_{\text{before separation}}} \cdot \frac{V_{\text{loading and scrubbing phases}}}{V_{\text{loading phase}}} \quad (1) $$

Where [cation]after separation and [cation]before separation are the concentration of the cation after and before the separation, respectively, and V is the volume of solution. Separations were considered efficient when cations recovery yields between 80 and 120 % were obtained.

The detection limit (LOD) were estimated based on the Guide to the expression of Uncertainty in Measurement (GUM, Eq. (2)) [28].

$$ \text{LOD} = s \cdot \frac{y}{x} \cdot \frac{t_{\text{student}}^2}{m} \cdot \sqrt{\frac{1}{p} + \frac{1}{n} + \frac{x_m^2}{\sum_{i=1}^{n} (x_i - x_m)^2}} \quad (2) $$

Where s·y/x is the standard error, m is the slope, p is the number of replicates for measuring one element, n is the number of sample in the calibration curve, x is the concentration used in the calibration curve
and $x_m$ is the average of x.

Repeatability (i.e. the closeness of agreement between independent results obtained with the same method on identical test material and under the same conditions) was determined by the relative standard deviation (RSD) of the measurement of an analyte after the three independent separations [29,30]. The repeatability is only used to evaluate the precision. In our laboratory, when the cationic impurities are determined after a separation step, the measurement relative uncertainty is set to a fixed uncertainty of 30 % (with a coverage factor of 2), including the calibration curve uncertainty, the reference material uncertainty, the repeatability, the yield, etc.

Eq. (3) was used to determine whether the measured values on the Morille CRM has a statistically significant bias compare to reference values. If the Zeta-score is lower than 2, the measured values are considered to have no statistically significant bias. If the Zeta-score between 2 and 3, the accuracy of the measured values is questionable. If the Zeta-score is higher than 3, the measured values are considered having a statistically significant bias.

$$Zeta\ -\ score = \frac{|\bar{x} - ref|}{\sqrt{u^2(\bar{x}) + u^2(ref)}} \quad (3)$$

Where $\bar{x}$ is the average of the measured values for a given element, $u(\bar{x})$ being the standard uncertainty of the measured values (i.e. relative standard uncertainty of 15 %) and $u(ref)$ the reference value standard uncertainty with a coverage factor $k = 1$.

### 3. Results and discussion

#### 3.1. Protocols selection

Separation results for the 14 cations with protocols A, B, C and D are summarized in Table 3. Cations recoveries were between 80 and 120 % for the 14 cations (Al, B, Ca, Cd, Cr, Cu, Fe, Ga, Mn, Mo, Ni, Pb, Si and

<caption>**Table 3**</caption>

Elemental recovery (%, mean) and one standard deviation (SD) of twenty-nine cations without U-Pu. “-” indicates the element was not analyzed.

<table><thead><tr><th rowspan="2">Element</th><th colspan="2">Protocol A<br>UTEVA<br>HNO<sub>3</sub></th><th colspan="2">Protocol B<br>UTEVA HNO<sub>3</sub>/<br>H<sub>2</sub>C<sub>2</sub>O<sub>4</sub></th><th colspan="2">Protocol C<br>UTEVA HNO<sub>3</sub>/<br>H<sub>2</sub>O<sub>2</sub></th><th colspan="2">Protocol D<br>UTEVA HNO<sub>3</sub></th></tr><tr><th>Mean</th><th>SD</th><th>Mean</th><th>SD</th><th>Mean</th><th>SD</th><th>Mean</th><th>SD</th></tr></thead><tbody><tr><td>Ag</td><td>-</td><td></td><td>103</td><td>2</td><td>96</td><td>1</td><td>-</td><td></td></tr><tr><td>Al</td><td>97</td><td>5</td><td>102</td><td>1</td><td>100</td><td>1</td><td>97</td><td>6</td></tr><tr><td>B</td><td>80</td><td>18</td><td>99</td><td>6</td><td>89</td><td>2</td><td>79</td><td>10</td></tr><tr><td>Ca</td><td>117</td><td>28</td><td>110</td><td>2</td><td>98</td><td>1</td><td>130</td><td>42</td></tr><tr><td>Cd</td><td>94</td><td>4</td><td>105</td><td>2</td><td>100</td><td>1</td><td>93</td><td>4</td></tr><tr><td>Ce</td><td>-</td><td></td><td>99</td><td>2</td><td>103</td><td>4</td><td>-</td><td></td></tr><tr><td>Cr</td><td>95</td><td>2</td><td>101</td><td>1</td><td>99</td><td>1</td><td>93</td><td>4</td></tr><tr><td>Cu</td><td>109</td><td>5</td><td>115</td><td>3</td><td>103</td><td>1</td><td>92</td><td>5</td></tr><tr><td>Fe</td><td>101</td><td>1</td><td>101</td><td>1</td><td>96</td><td>1</td><td>98</td><td>3</td></tr><tr><td>Ga</td><td>94</td><td>1</td><td>98</td><td>9</td><td>95</td><td>3</td><td>93</td><td>3</td></tr><tr><td>La</td><td>-</td><td></td><td>96</td><td>3</td><td>101</td><td>4</td><td>-</td><td></td></tr><tr><td>Mg</td><td>-</td><td></td><td>97</td><td>1</td><td>97</td><td>1</td><td>-</td><td></td></tr><tr><td>Mn</td><td>96</td><td>5</td><td>103</td><td>1</td><td>101</td><td>1</td><td>96</td><td>5</td></tr><tr><td>Mo</td><td>96</td><td>4</td><td>105</td><td>1</td><td>101</td><td>2</td><td>93</td><td>6</td></tr><tr><td>Na</td><td>-</td><td></td><td>106</td><td>3</td><td>103</td><td>1</td><td>-</td><td></td></tr><tr><td>Nd</td><td>-</td><td></td><td>94</td><td>8</td><td>100</td><td>8</td><td>-</td><td></td></tr><tr><td>Ni</td><td>102</td><td>4</td><td>108</td><td>1</td><td>99</td><td>1</td><td>97</td><td>3</td></tr><tr><td>Pb</td><td>96</td><td>2</td><td>93</td><td>2</td><td>95</td><td>4</td><td>94</td><td>3</td></tr><tr><td>Pd</td><td>-</td><td></td><td>99</td><td>3</td><td>102</td><td>5</td><td>-</td><td></td></tr><tr><td>Rh</td><td>-</td><td></td><td>99</td><td>2</td><td>103</td><td>3</td><td>-</td><td></td></tr><tr><td>Sb</td><td>-</td><td></td><td>96</td><td>9</td><td>101</td><td>6</td><td>-</td><td></td></tr><tr><td>Se</td><td>-</td><td></td><td>103</td><td>1</td><td>108</td><td>5</td><td>-</td><td></td></tr><tr><td>Si</td><td>87</td><td>7</td><td>82</td><td>4</td><td>100</td><td>1</td><td>90</td><td>5</td></tr><tr><td>Sn</td><td>-</td><td></td><td>86</td><td>3</td><td>88</td><td>2</td><td>-</td><td></td></tr><tr><td>Sr</td><td>-</td><td></td><td>100</td><td>3</td><td>105</td><td>5</td><td>-</td><td></td></tr><tr><td>Ti</td><td>-</td><td></td><td>108</td><td>1</td><td>104</td><td>1</td><td>-</td><td></td></tr><tr><td>V</td><td>-</td><td></td><td>104</td><td>1</td><td>102</td><td>2</td><td>-</td><td></td></tr><tr><td>Y</td><td>-</td><td></td><td>99</td><td>2</td><td>104</td><td>4</td><td>-</td><td></td></tr><tr><td>Zn</td><td>102</td><td>5</td><td>106</td><td>2</td><td>90</td><td>2</td><td>95</td><td>4</td></tr></tbody></table>

Zn) except for Ca in the protocol D (130 %). The RSD for the 14 cations were below 10 % for the protocols B and C. For protocol A and D, the RSD were also below 10 % except for B and Ca for when the RSD were between 13 and 32 %. It should be noticed the first series of separation were performed and analyzed before the second and third series. The results of the first series for Ca were incoherent due to a pollution and not taken into account. Thus, the results presented here for Ca are the average of the second and the third separations. These results showed that the 14 cations were not retained on the resin for protocols A, B, C and D. Separation protocols were found to be effective for these cations.

The four protocols have similar performances, although protocols B and C appear to have better repeatability. Indeed, the choice of protocols used for the rest of this study was based on practical considerations. Protocol A required two scrubbing steps, compared to only one for the other protocols, that are more time-consuming for routine analysis. Protocol C involves a valence adjustment of uranium and plutonium by hydrogen peroxide and have already proved efficient to fix it [21]. The protocol C is routinely applied in the laboratory to separate U and Pu. Thus it will help separating the cations, U and Pu on the same aliquot sample saving a considerable amount of time. Protocol D using nitric acid and a TEVA resin should not retain all the plutonium unless Pu valence adjustment is performed using the Fe(II)/NaNO₂ method [19]. Therefore, the Fe and Na analysis is not possible with protocol D. Protocols B and C seems to be more adapted to separate the cations from uranium and plutonium in routine work. Therefore, they are used for the rest of the study.

Then, 6 new cations (Ag, Mg, Na, Sn, Ti and V) were added to create the “multi 20c” solution. Using protocol B and C, the six cations recovery were between 85 and 110 % with a RSD between 1 and 3 % (Table 3). Finally, separation tests were performed on 9 new cations (multi9c solution). Using protocols B and C, the nine cations (Ce, La, Nd, Pd, Rh, Sb, Se, Sr and Y) were recovered between 95 and 110 % with a RSD between 2 and 10 %. The 29 cations were not retained onto the resin for protocol B and C.

#### 3.2. Protocols verification for the quantification of cationic impurities in uranium and plutonium matrix

Separation protocols were performed on EQRAIN U-Pu solution to ensure it is cation free. Results are summarized in Table 4.

Most of the results are below the limit of detection. A Ca pollution

<caption>**Table 4**</caption>

Cations concentrations (mg L⁻¹) in feeding and scrubbing phases after EQRAIN U-Pu separation.

<table><thead><tr><th>Element</th><th>Protocol B<br>UTEVA - HNO<sub>3</sub>/H<sub>2</sub>C<sub>2</sub>O<sub>4</sub></th><th>Protocol C<br>UTEVA - HNO<sub>3</sub>/H<sub>2</sub>O<sub>2</sub></th></tr></thead><tbody><tr><td>Ag</td><td>&lt; 0.4</td><td>&lt; 0.4</td></tr><tr><td>Al</td><td>&lt; 0.3</td><td>&lt; 0.3</td></tr><tr><td>B</td><td>&lt; 0.2</td><td>&lt; 0.2</td></tr><tr><td>Ca</td><td>&lt; 0.6</td><td>2.5 ± 0.3</td></tr><tr><td>Cd</td><td>&lt; 0.4</td><td>&lt; 0.4</td></tr><tr><td>Cr</td><td>&lt; 0.3</td><td>&lt; 0.3</td></tr><tr><td>Cu</td><td>&lt; 0.3</td><td>&lt; 0.3</td></tr><tr><td>Fe</td><td>&lt; 0.4</td><td>&lt; 0.4</td></tr><tr><td>Ga</td><td>&lt; 0.4</td><td>&lt; 0.4</td></tr><tr><td>Mg</td><td>&lt; 0.4</td><td>&lt; 0.4</td></tr><tr><td>Mn</td><td>&lt; 0.4</td><td>&lt; 0.4</td></tr><tr><td>Mo</td><td>&lt; 0.4</td><td>&lt; 0.4</td></tr><tr><td>Na</td><td>&lt; 0.1</td><td>&lt; 0.1</td></tr><tr><td>Ni</td><td>&lt; 0.3</td><td>&lt; 0.3</td></tr><tr><td>Pb</td><td>&lt; 0.3</td><td>&lt; 0.3</td></tr><tr><td>Si</td><td>&lt; 0.6</td><td>&lt; 0.6</td></tr><tr><td>Sn</td><td>&lt; 0.3</td><td>&lt; 0.3</td></tr><tr><td>Ti</td><td>&lt; 0.3</td><td>&lt; 0.3</td></tr><tr><td>V</td><td>&lt; 0.3</td><td>&lt; 0.3</td></tr><tr><td>Zn</td><td>&lt; 0.4</td><td>&lt; 0.4</td></tr><tr><td>U</td><td>&lt; 0.5</td><td>&lt; 0.5</td></tr><tr><td>Pu</td><td>&lt; 0.4</td><td>16.3 ± 5.1</td></tr></tbody></table>
was observed in the protocol C. As the Ca pollution did not occur in protocol B, the EQRAIN U-Pu solution is not the pollution source. Such pollution was already observed in one of the separations made without U-Pu. These detection limits (< 0.6 mg L⁻¹) are enough to not affect the interpretation of results for the EQRAIN U-Pu solution spiked with element at 50 mg L⁻¹.

No uranium was recovered in the cations fraction for the two protocols. No plutonium was recovered in the cations fraction in the protocol B. In our experiment, Pu is still retained in the resin contrary to a previous study where the Pu is eluted with a 4 mol L⁻¹ HNO₃/0.1 mol L⁻¹ H₂C₂O₂ solution (similar solution as used in this study) [31]. For protocol C, a part of Pu was eluting in feeding and scrubbing phases, which corresponds to 10 % of Pu in EQRAIN U-Pu solution. This plutonium concentration ([Pu] = 16 mg L⁻¹) is low enough to have no effect on ICP measurements.

Recoveries for the 14 cations in a U-Pu matrix using protocols B and C were summarized in Table 5. Recoveries were between 85 and 110 % for all the cations. The RSD were lower than 6 % except for Si that shown a RSD of 17 % in protocol C. The separation of 14 cations from U-Pu is efficient using protocols B and C.

Similar cations behavior was observed in either U-Pu absence or presence.

### 3.3. Method validation for the quantification of cationic impurities in a certified reference material

Protocols B and C were evaluated using the Morille CRM. Once the separation process was realized on each of the three dissolution, the mass fraction of each cation were measured by ICP-MS or ICP-OES. Results are summarized in Table 6 and in the supplementary information.

Recoveries were between 80 and 120 % for 20 cations (Ag, Be, Bi, Cd, Co, Cr, Cu, Dy, Eu, Gd, In, Li, Mo, Ni, Pb, Sm, Sn, Ti, V and W) with a repeatability below 25 %. The zeta-scores are less than 2, indicating that the measured values are not statistically significantly biased.

Ba was recovered at 100 % for protocol C with a repeatability below 5 % and a zeta-score less than 2, indicating the measurement is in agreement with the certified value. Ba was recovered at 162 % for protocol B. The zeta-score falls within the range of 2 to 3, suggesting that the observed values may be unreliable. The occurrence of this phenomenon has been attributed to the potential for contamination from the oxalic acid employed. Afterward, Ba will be analyzed only using protocol C.

Separations results for Fe were validated with a zeta-score less than 2. Fe was analyzed by ICP-OES to avoid ArO⁺ interference in ICP-MS. ArO⁺ interference can also be overcome using a collision and/or

<caption>**Table 5**</caption>

Elemental recovery (%, mean) and one standard deviation (SD) of fourteen cations in a U-Pu matrix.

<table><thead><tr><th rowspan="2">Element</th><th colspan="2">Protocol B<br>UTEVA - HNO<sub>3</sub>/H<sub>2</sub>C<sub>2</sub>O<sub>4</sub></th><th colspan="2">Protocol C<br>UTEVA - HNO<sub>3</sub>/H<sub>2</sub>O<sub>2</sub></th></tr><tr><th>Mean</th><th>SD</th><th>Mean</th><th>SD</th></tr></thead><tbody><tr><td>Al</td><td>90</td><td>1</td><td>92</td><td>1</td></tr><tr><td>B</td><td>95</td><td>1</td><td>100</td><td>1</td></tr><tr><td>Ca</td><td>91</td><td>1</td><td>93</td><td>1</td></tr><tr><td>Cd</td><td>87</td><td>1</td><td>89</td><td>1</td></tr><tr><td>Cr</td><td>105</td><td>1</td><td>99</td><td>2</td></tr><tr><td>Cu</td><td>94</td><td>1</td><td>97</td><td>2</td></tr><tr><td>Fe</td><td>94</td><td>1</td><td>98</td><td>2</td></tr><tr><td>Ga</td><td>84</td><td>1</td><td>85</td><td>2</td></tr><tr><td>Mn</td><td>94</td><td>1</td><td>97</td><td>1</td></tr><tr><td>Mo</td><td>95</td><td>1</td><td>100</td><td>2</td></tr><tr><td>Ni</td><td>98</td><td>1</td><td>98</td><td>2</td></tr><tr><td>Pb</td><td>91</td><td>1</td><td>95</td><td>2</td></tr><tr><td>Si</td><td>96</td><td>2</td><td>108</td><td>17</td></tr><tr><td>Zn</td><td>96</td><td>1</td><td>96</td><td>6</td></tr></tbody></table>

reaction cell with gases such as CH₄, NH₃, N₂O, H₂ and H₂-He [14,32–35]. ICP-MS with the collision and/or reaction cell can be used to improve the detection limit compared to ICP-OES.

Th, mainly in + IV valence, was not recovered after separation, it was retained onto the resin (recovery of 11 % and a zeta-score upper than 3). A similar cation behavior of Th and U has been exhibited on UTEVA resin in nitric acid [15]. U and Th can be co-eluted using a 0.1 mol L⁻¹ HNO₃ / 0.05 mol L⁻¹ H₂C₂O₄ mixture [36]. To separate Th from U, hydrochloric acid has been proved efficient [15,37–39]

Zr was totally recovered using protocol B (recovery of 112 % and zeta-score less than 2) because using oxalic acid as complexing agent, but not with protocol C (recovery of 16 % and zeta-score upper than 3). Zr retention by UTEVA resin in concentrated nitric acid had already been demonstrated [40–42]. If needed, an additional step using oxalic acid can be added to the protocol C to eluate Zr from UTEVA resin [43].

Al, Ca and Si could not be quantified. The ICP-OES used, being nuclearized, does not reach such specifications. The ICP-MS used is too polluted to quantify B and Mn for these concentrations. A Mg and Zn pollution was observed and could be coming from the tubes used for the analysis (for Zn) or may have occurred during manipulations. During the previous experiments, recoveries of about 100 % were achieved for these cations (Al, B, Ca, Mg, Mn, Si and Zn). With special care (improving the detection limit using ICP-MS, avoiding contamination, using a cleaner instrument), it seems possible to analyze them using these two protocols.

These results showed that 23 cations (Ag, Ba, Be, Bi, Cd, Co, Cr, Cu, Dy, Eu, Fe, Gd, In, Li, Mo, Ni, Pb, Sm, Sn, Ti, V, W and Zr) could be analyzed using the two protocols in a U-Pu matrix. For Al, B, Ca, Mg, Mn, Si and Zn, with special care it is possible to analyze them. Th analysis is however not possible with these protocols.

Using the dilution method, Be, Dy, Eu, Gd and Sm cannot be analyzed at such specifications (Table 6). For the others 19 elements (Ag, Ba, Bi, Cd, Co, Cr, Cu, Fe, In, Li, Mo, Ni, Pb, Sn, Th, Ti, V, W and Zr), the recoveries were between 90 and 120 %. It should be noticed that Th can be analyzed using the dilution method compare to using the separation protocol.

Without removing the U matrix from the cations, it is not possible to analyze Be, Dy, Eu, Gd and Sm at such specifications. Elemental recoveries were similar for other elements as well as their repeatability. Removing U from the analyzed sample prevents pollution device and avoids long rinse cycle.

### 3.4. Comparison of the detection limits

Detection limits were estimated for each separation method and compared to the ones obtained using the dilution method, which is the method currently used in the laboratory. Detection limits are summarized in Table 7.

Detection limits obtained are between 0.05 and 3 mg kg⁻¹ of U using separation and between 0.05 and 35 mg kg⁻¹ of U for the sample dilution. Similar detection limits were obtained for 20 cations (Ag, Ba, Be, Bi, Cd, Cr, Dy, Eu, Gd, In, Li, Mo, Pb, Sm, Sn, Th, Ti, V, W and Zr). Separation helps obtaining better detection limits for Co (sample dilution: 0.5 mg kg⁻¹; separation: 0.05 mg kg⁻¹), Cu (sample dilution: 35 mg kg⁻¹; separation: 1 mg kg⁻¹) and Ni (sample dilution: 16 mg kg⁻¹; separation: 0.03 mg kg⁻¹).

In another study, better detection limits were obtained: LOD as low as 0.001 mg kg⁻¹ [14] and LOD as low as 0.05 mg kg⁻¹ in this study. The factor 50 on the LOD can be explained by (1) the ICP-MS used in this study is nuclearized and of an old generation, that limits its sensitivity. Typical sensitivity for ¹¹⁵In is about 40,000 cps (µg L⁻¹)⁻¹ in our instrument whereas sensitivity upper than 1,000,000 cps (µg L⁻¹)⁻¹ can be obtained with new ICP-MS. (2) The blanks of the instrument used are not as clean as desired due to its long use with very different matrices. It is possible to achieve better detection limit by using a cleaner instrument. However, rinsing it during a long time is prohibited, as the effluent volume will be
<table><caption>**Table 6**

Elemental recovery (%, mean), one standard deviation (SD) and certified mass fraction of cations in the Morille CRM.</caption><thead><tr><th rowspan="3">Element</th><th colspan="6">Separation method</th><th colspan="3">Dilution method</th><th rowspan="3">Certified values<br>(mg kg<sup>-1</sup> of U)</th></tr><tr><th colspan="3">Protocol B</th><th colspan="3">Protocol C</th><th rowspan="2">Mean</th><th rowspan="2">SD</th><th rowspan="2">Zeta</th></tr><tr><th colspan="3">UTEVA - HNO<sub>3</sub>/H<sub>2</sub>C<sub>2</sub>O<sub>4</sub></th><th colspan="3">UTEVA - HNO<sub>3</sub>/H<sub>2</sub>O<sub>2</sub></th></tr><tr><th></th><th>Mean</th><th>SD</th><th>Zeta</th><th></th><th>Mean</th><th>SD</th><th>Zeta</th><th></th><th></th><th></th></tr></thead><tbody><tr><td>Ag</td><td>121</td><td>14</td><td>1.1</td><td></td><td>110</td><td>11</td><td>0.6</td><td>121</td><td>10</td><td>1.1</td><td>10.4 ± 1.6</td></tr><tr><td>Al*</td><td>/</td><td></td><td></td><td>/</td><td></td><td></td><td></td><td></td><td></td><td></td><td>99 ± 6</td></tr><tr><td>B</td><td>/</td><td></td><td></td><td>/</td><td></td><td></td><td></td><td></td><td></td><td></td><td>3.8 ± 1.6</td></tr><tr><td>Ba</td><td>162</td><td>9</td><td>2.5</td><td>100</td><td>5</td><td>0.0</td><td>99</td><td>6</td><td>0.1</td><td>9.6 ± 0.4</td><td>5.4 ± 0.6</td></tr><tr><td>Be</td><td>79</td><td>6</td><td>1.6</td><td>76</td><td>11</td><td>1.9</td><td></td><td></td><td></td><td></td><td>24.2 ± 1.9</td></tr><tr><td>Bi</td><td>98</td><td>5</td><td>0.1</td><td>91</td><td>5</td><td>0.6</td><td>94</td><td>5</td><td>0.4</td><td>93 ± 8</td><td>5.4 ± 0.6</td></tr><tr><td>Ca*</td><td>/</td><td></td><td></td><td>/</td><td></td><td></td><td></td><td></td><td></td><td></td><td>9.8 ± 0.7</td></tr><tr><td>Cd</td><td>120</td><td>4</td><td>1.0</td><td>112</td><td>5</td><td>0.6</td><td>113</td><td>3</td><td>0.7</td><td>9.8 ± 0.7</td><td>9.8 ± 2.0</td></tr><tr><td>Co</td><td>104</td><td>7</td><td>0.2</td><td>99</td><td>7</td><td>0.1</td><td>99</td><td>7</td><td>0.0</td><td>9.8 ± 0.7</td><td>9.8 ± 2.0</td></tr><tr><td>Cr</td><td>114</td><td>15</td><td>0.8</td><td>96</td><td>5</td><td>0.2</td><td>99</td><td>6</td><td>0.1</td><td>9.8 ± 0.7</td><td>9.8 ± 2</td></tr><tr><td>Cu</td><td>98</td><td>4</td><td>0.1</td><td>100</td><td>14</td><td>0.0</td><td>92</td><td>3</td><td>0.6</td><td>50.2 ± 1.0</td><td>50.2 ± 1.0</td></tr><tr><td>Dy</td><td>96</td><td>9</td><td>0.3</td><td>89</td><td>10</td><td>0.7</td><td>/</td><td></td><td></td><td>0.50 ± 0.06</td><td>0.50 ± 0.06</td></tr><tr><td>Eu</td><td>106</td><td>6</td><td>0.4</td><td>90</td><td>8</td><td>0.7</td><td>/</td><td></td><td></td><td>0.52 ± 0.03</td><td>0.52 ± 0.03</td></tr><tr><td>Fe*</td><td>108</td><td>6</td><td>0.5</td><td>98</td><td>16</td><td>0.1</td><td>/</td><td></td><td></td><td>211.6 ± 6.5</td><td>211.6 ± 6.5</td></tr><tr><td>Gd</td><td>100</td><td>6</td><td>0.0</td><td>98</td><td>9</td><td>0.2</td><td>/</td><td></td><td></td><td>0.56 ± 0.06</td><td>0.56 ± 0.06</td></tr><tr><td>In</td><td>98</td><td>6</td><td>0.1</td><td>92</td><td>3</td><td>0.6</td><td>96</td><td>4</td><td>0.2</td><td>9.4 ± 1.0</td><td>9.4 ± 1.0</td></tr><tr><td>Li</td><td>108</td><td>9</td><td>0.5</td><td>102</td><td>8</td><td>0.1</td><td>109</td><td>5</td><td>0.6</td><td>5.0 ± 0.2</td><td>5.0 ± 0.2</td></tr><tr><td>Mg</td><td>/</td><td></td><td></td><td>/</td><td></td><td></td><td></td><td></td><td></td><td>19.3 ± 1.5</td><td>19.3 ± 1.5</td></tr><tr><td>Mn</td><td>/</td><td></td><td></td><td>/</td><td></td><td></td><td></td><td></td><td></td><td>24.5 ± 0.5</td><td>24.5 ± 0.5</td></tr><tr><td>Mo</td><td>111</td><td>5</td><td>0.7</td><td>104</td><td>3</td><td>0.3</td><td>104</td><td>2</td><td>0.3</td><td>147 ± 5</td><td>147 ± 3</td></tr><tr><td>Ni</td><td>111</td><td>8</td><td>0.7</td><td>109</td><td>12</td><td>0.6</td><td>92</td><td>6</td><td>0.6</td><td>147 ± 5</td><td>147 ± 3</td></tr><tr><td>Pb</td><td>110</td><td>16</td><td>0.6</td><td>115</td><td>6</td><td>0.9</td><td>103</td><td>15</td><td>0.2</td><td>101 ± 3</td><td>101 ± 3</td></tr><tr><td>Si*</td><td>/</td><td></td><td></td><td>/</td><td></td><td></td><td></td><td></td><td></td><td>100 ± 8</td><td>100 ± 8</td></tr><tr><td>Sm</td><td>113</td><td>11</td><td>0.6</td><td>111</td><td>6</td><td>0.5</td><td>/</td><td></td><td></td><td>0.50 ± 0.12</td><td>0.50 ± 0.12</td></tr><tr><td>Sn</td><td>102</td><td>6</td><td>0.1</td><td>102</td><td>8</td><td>0.1</td><td>98</td><td>2</td><td>0.1</td><td>18.5 ± 5.6</td><td>18.5 ± 5.6</td></tr><tr><td>Th</td><td>11</td><td>0</td><td>13</td><td>11</td><td>1</td><td>13</td><td>107</td><td>5</td><td>0.4</td><td>6.2 ± 0.8</td><td>6.2 ± 0.8</td></tr><tr><td>Ti</td><td>115</td><td>2</td><td>0.9</td><td>104</td><td>3</td><td>0.3</td><td>107</td><td>5</td><td>0.5</td><td>49.2 ± 2.6</td><td>49.2 ± 2.6</td></tr><tr><td>V</td><td>111</td><td>4</td><td>0.6</td><td>103</td><td>5</td><td>0.2</td><td>99</td><td>5</td><td>0.0</td><td>48.7 ± 2.8</td><td>48.7 ± 2.8</td></tr><tr><td>W</td><td>108</td><td>4</td><td>0.5</td><td>99</td><td>5</td><td>0.1</td><td>101</td><td>4</td><td>0.1</td><td>100 ± 9</td><td>100 ± 9</td></tr><tr><td>Zn</td><td>/</td><td></td><td></td><td>/</td><td></td><td></td><td></td><td></td><td></td><td>98.6 ± 5.5</td><td>98.6 ± 5.5</td></tr><tr><td>Zr</td><td>112</td><td>4</td><td>0.7</td><td>16</td><td>3</td><td>20</td><td>104</td><td>5</td><td>0.3</td><td>59.9 ± 4.1</td><td>59.9 ± 4.1</td></tr></tbody></table>

Uncertainties of the certified mass fraction are given with a coverage factor of 2. Measurements were performed by ICP-MS except for elements with “*” where ICP-OES was used. “/” indicates the elements could not be quantified. “-” indicates the elements were not analyzed. Zr and Th mass fractions in the Morille CRM are indicative values and not certified values.

<table><caption>**Table 7**

Detection limits in mg kg⁻¹ of U of the Morille CRM with “/” where elements cannot be analyzed with the protocol.</caption><thead><tr><th>Elements</th><th>Separation method</th><th>Dilution method</th></tr></thead><tbody><tr><td>Ag</td><td>0.1</td><td>0.05</td></tr><tr><td>Ba</td><td>0.6</td><td>0.8</td></tr><tr><td>Be</td><td>0.5</td><td>4</td></tr><tr><td>Bi</td><td>0.1</td><td>0.05</td></tr><tr><td>Cd</td><td>0.1</td><td>0.2</td></tr><tr><td>Co</td><td>0.05</td><td>0.5</td></tr><tr><td>Cr</td><td>3</td><td>3</td></tr><tr><td>Cu</td><td>1</td><td>35</td></tr><tr><td>Dy</td><td>0.1</td><td>0.1</td></tr><tr><td>Eu</td><td>0.05</td><td>0.02</td></tr><tr><td>Gd</td><td>0.3</td><td>0.1</td></tr><tr><td>In</td><td>0.05</td><td>0.05</td></tr><tr><td>Li</td><td>0.2</td><td>1</td></tr><tr><td>Mo</td><td>0.1</td><td>0.6</td></tr><tr><td>Ni</td><td>0.3</td><td>16</td></tr><tr><td>Pb</td><td>0.1</td><td>0.4</td></tr><tr><td>Sm</td><td>0.2</td><td>0.2</td></tr><tr><td>Sn</td><td>0.05</td><td>0.3</td></tr><tr><td>Th</td><td>/</td><td>0.3</td></tr><tr><td>Ti</td><td>1</td><td>1</td></tr><tr><td>V</td><td>0.4</td><td>0.4</td></tr><tr><td>W</td><td>0.1</td><td>0.05</td></tr><tr><td>Zr</td><td>0.1</td><td>0.1</td></tr></tbody></table>

too high and is considered radioactive and needs to be recycled before evacuation. Using a cleaner and a more sensitive instrument will help to obtain detection limit comparable of the previous study, which used an

ICP-MS on a lab bench [14].

Another way to decrease the detection limit is to reduce the sample dilution required to its analysis. As HNO₃ concentration has to be adjusted at 0.5 mol L⁻¹, elution phase (loading and washing) are diluted 6 and 8 time for protocols B and C before the ICP-MS analysis, respectively. The elution phase can be evaporated to dryness and dissolved again in the appropriate volume of 0.5 mol L⁻¹ HNO₃, which can help to reduce the detection limit by a factor of 10. It will be necessary to check that the cations have not been lost during the evaporation step before using this approach.

## 4. Conclusions

This study aims at developing chromatographic separation procedure to separate cations from U-Pu. The protocols were tested on simulated solutions of 29 cations in absence of U-Pu and 14 cations in a U-Pu matrix. Uranium and plutonium were fixed onto the resin using protocol B (UTEVA resin with HNO₃/H₂C₂O₄ mixture as eluent) and C (UTEVA resin with HNO₃/H₂O₂ mixture as eluent). Separation protocols were found to be effective with recovery yields between 80 and 120 %.

Then, the separations performed on the Morille CRM showed satisfactory results for most of the elements. A Ba pollution from oxalic acid used in protocol B was observed. Using protocol C, Zr is fixed onto the resin. To eluate Zr, oxalic acid needs to be used. Moreover, the Th behavior, a tetravalent actinide, did not help us to recover it with the other cations in the feeding and scrubbing phases. To recover thorium independently of U and Pu, using hydrochloric acid is required. Since hydrochloric acid is corrosive to glove boxes, its use is avoided. Combining the studies on the CRM and on the simulated solutions, it is
possible to analyze 41 cations (Al, Ag, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Dy, Eu, Fe, Ga, Gd, In, La, Li, Mg, Mn, Mo, Na, Nd, Ni, Pd, Pb, Rh, Sb, Se, Si, Sm, Sn, Sr, Ti, V, W, Y, Zn and Zr) with the two selected protocols in a U-Pu matrix.

Without separating U from the cations it is impossible to analyze Be, Dy, Eu, Gd and Sm in the CRM at these concentrations.

These separation protocols were implemented to certify a Pu-based reference material and to samples for irradiation experiment. Detection limits in the order of µg g⁻¹ of powder were obtained. Furthermore, as Th and Np are fixed onto the resin, these protocols could be extended for cationic impurities analysis in Th or Np-based materials. It should be notice Np is only fixed on the resin using protocol C. The oxalic acid used in the protocol B is a complexing agent of Np.

### CRediT authorship contribution statement

**Marion Hernandez:** Writing – original draft, Visualization, Methodology, Investigation. **Alexandre Quetem:** Writing – review & editing, Supervision, Methodology, Conceptualization. **Laure Montreuil:** Investigation. **Christophe Maillard:** Methodology. **Sarah Baghdadi:** Writing – review & editing, Supervision, Conceptualization.

### Declaration of competing interest

There are no conflicts to declare.

### Acknowledgments

The authors are grateful to Vincent Dalier, Sandrine Le Roux, Magali Rousset (CEA/MAR/DES/DMRC/SASP/LAAT), Sophie Gracia and Xavier Heres (CEA/MAR/DES/DMRC/SPTC/LCIS) for their help with ICP-MS and ICP-OES measurements.

### Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.sab.2025.107136.

### Data availability

The data supporting this article are available from the corresponding authors on reasonable request.

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