A simple mixed-micelle process for selective microextraction of trace Th(IV) from lanthanide matrices

Prolonged exposure to thorium and its compounds can cause severe and irreversible damage to the bones and the kidneys, highlighting the need for its selective separation from other rare earth elements, particularly uranium. Traditional detection methods for Th(IV) are often time-consuming and costly. In this study, we present a simple and efficient mixed micelle-mediated microextraction method for Th(IV). Thorium was complexed with Solochrome Cyanine R (SCR) and extracted using Triton X-114 at 45 °C with KNO₃ and cetyltrimethylammonium bromide (CTAB) to enhance phase separation and extraction efficiency. The method achieved >95% extraction efficiency, a 100-fold preconcentration factor, and a detection limit of 0.8 ng mL⁻¹. Thorium was completely extracted at pH ≥ 3 in the presence of U(VI) and lanthanides (Nd(III), Ce(III), and Gd(III)). Recovery experiments with reference materials, freshwater, and synthetic mixtures confirmed the accuracy and applicability of the method.

1 Introduction

Thorium (Th) is a naturally occurring radioactive element that is approximately four times more abundant than uranium in the Earth’s crust (Sharma et al., 2024). It is commonly present in monazite sands, igneous rocks, polluted soils, and water sources. Human exposure to thorium through air, water, or food can cause severe health complications, including kidney and liver dysfunction, as well as skeletal damage. To mitigate the health risks posed by thorium exposure, innovative detection methods, such as nanopore sensors and removal techniques, have been developed for heavy metal contamination in water and soil (Keshta et al., 2024; Al-Labadi et al., 2025; Hussain et al., 2025; Javeria et al., 2025a, 2025b; Soni et al., 2025; Zango et al., 2025). The World Health Organization (WHO) has set a maximum permissible limit of 20 μg L⁻¹ for Th(IV) in drinking water (Sadeghi and Davami, 2019). Owing to its unique physical and nuclear properties, thorium is widely used in industries such as ceramics, metallurgy, and optics and is particularly regarded as a promising alternative nuclear fuel (Tarafder et al., 2016). Its abundance and favorable fuel characteristics have drawn significant attention to the thorium fuel cycle in recent years (Humphrey and Khandaker, 2018). However, increasing thorium use also raises concerns about environmental contamination and radioactive exposure risks (Moghaddam et al., 2018), necessitating the development of reliable monitoring and remediation technologies. Accurate and selective quantification of Th(IV) at trace levels remains a major analytical challenge due to its low natural abundance in aqueous samples and the presence of matrix interferences (Rožmarić et al., 2009; Basque et al., 2023; Gao et al., 2023). A wide range of methods, such as liquid–liquid extraction (Tarafder et al., 2016; Sadeghi and Davami, 2019), ion exchange (Deb et al., 2008), electrodeposition (Reynier et al., 2022), extraction chromatography (Perez-Tribouillier et al., 2019), and solid-phase extraction (SPE) (Li et al., 2017; Ding et al., 2019; Mahanty and Mohapatra, 2020), have been employed to separate and preconcentrate Th(IV) before determination using techniques, such as Inductively Coupled PlasmaOptical Emission Spectroscopy (ICP-OES) or Inductively Coupled PlasmaOptical Emission Mass Spectroscopy (ICP-MS). While these approaches are effective, they often suffer from drawbacks such as high reagent consumption, long processing times, and limited selectivity in complex matrices (Xiu et al., 2019). More recent studies have also investigated advanced separation strategies and wastewater treatment technologies aimed at sustainable removal of toxins, dyes, antibiotics, and radioactive contaminants (Abd El-Hay and Gouda, 2016; Wang et al., 2019; Armaya’u et al., 2024; Nezami et al., 2024; Abbas et al., 2025; Ismail et al., 2025; Keshta et al., 2025; Abodif et al., 2026). In this context, cloud point extraction (CPE) has emerged as a green and attractive alternative to conventional solvent-based extraction methods. It employs non-ionic surfactants that become phase-separated upon reaching the cloud point temperature, enabling the efficient extraction of hydrophobic complexes (Saha et al., 2016; Pawar et al., 2017; Akl and Hegazy, 2020). CPE offers advantages such as low toxicity, biodegradability, and the elimination of volatile organic solvents. However, traditional CPE is often less effective for ionic metal complexes due to electrostatic repulsion, which hinders phase separation (Shariati et al., 2008). To overcome these limitations, mixed micelle-mediated extraction (MME) techniques, which combine cationic and non-ionic surfactants, have been developed. These systems enhance extraction efficiency by neutralizing the charge of chelating agents, thereby increasing complex hydrophobicity and improving phase separation (Shariati et al., 2008; AlSalem et al., 2024; Şenol et al., 2025). Despite these advancements, there is still a lack of selective, eco-friendly, and sensitive methods for thorium extraction from real water and geological samples, particularly in the presence of uranium and lanthanides. To address this gap, the present study introduces a novel mixed-micelle cloud point extraction (Mixed-MM-CPE) approach that employs SCR as a chelating agent, CTAB as a cationic surfactant, and Triton X-114 as a neutral surfactant (Figure 1). The proposed method offers improved selectivity by ensuring that U(VI) and lanthanide ions (Nd(III), Ce(III), and Gd(III)) do not interfere under the same experimental conditions, while also providing a greener and more sustainable extraction pathway. The developed procedure was optimized with respect to pH, temperature, surfactant and reagent concentrations, and equilibrium time. Its validity was confirmed using certified reference samples and real-environmental matrices. Thorium concentrations were measured by ICP-OES, and the results were cross-validated using x-ray fluorescence (XRF). The findings not only demonstrate the reliability and selectivity of the Mixed-MM-CPE method but also highlight its potential applications in environmental monitoring, nuclear waste management, and sustainable wastewater treatment technologies. This study contributes to filling the current research gap by presenting a selective, environmentally benign, and cost-effective approach for thorium extraction, paving the way for future applications in analytical and environmental chemistry.

Figure 1

Figure 1. Solochrome Cyanine R (sodium salt) structure.

2 Experiment

2.1 Instruments

The concentration of Th(IV) in each sample utilized in this experiment was determined by Perkin Elmer ICP-OES (Optima 8300, USA). The adjusted instrument conditions applied to evaluate the Th(IV) concentration are presented in Table 1. Meanwhile, an XRF spectrometer model (PANalytical Axios FAST, Netherlands) was employed to determine the elemental content in the geological samples. A thermostatic shaker (JSR Model JSSB-30T, Korea) was also employed to maintain a consistent temperature throughout the experiments. Using a CH90-2 central centrifuge machine sped up the separation of mixed micelles.

Table 1

Table 1. The adjusted settings of ICP-OES instruments.

2.2 Chemicals, reagents, and solutions

All solvents and organic and inorganic salts used in this experiment were of pure analytical grade. The sodium salt of Solochrome Cyanine R (SCR), the chelating agent, and Th(Cl)₄·6H₂O were both obtained from the German company, Merck. The cetyltrimethylammonium bromide (CTAB) salt was used as the ion pairing agent, while Triton X-114 was the organic non-ionic surfactant, and both were from purchased from Sigma-Aldrich, US. Stock solutions of 100 mg L⁻¹ Th(Cl)₄·6H2O and 1.0 × 10⁻² mol L⁻¹ SCR were prepared in double-distilled (DD) water. The experimental samples were prepared fresh every day using definite volumes taken from the stock solution and then diluted to a specific volume with deionized water. Incidentally, the buffer solutions used in the experiments were as follows: glycine/HCl to adjust the pH to 2.0–3.0, acetic acid /Na-acetate to adjust the pH to 4.0–6.0, and boric acid/borax to adjust the pH to 7.0–9.0. The aqueous solutions of the synthetic mixtures and interfering ions were prepared by dissolving calculated amounts of the inorganic salts in deionized water.

2.3 Methodology and experimental design

The experiments were carried out in 50-mL centrifuge tubes. A specific volume of Th(IV) stock solution was combined with 500 μL of SCR (1.0 × 10⁻² mol L⁻¹) and 500 μL of CTAB (1.0 × 10⁻² mol L⁻¹). Then, 5.0 mL of KNO₃ solution (1.0 mol L⁻¹) was added as a supporting electrolyte, followed by 3 mL of Triton X-114 (4% w/v). The pH of the solutions was adjusted to the desired value using buffer solutions, and the final volume was diluted to 50 mL with deionized water. All sample tubes were shaken at 25 °C for 10 min and then placed in a thermostatic shaker at 45 °C for 5 min. After incubation, the samples were centrifuged at 4,000 rpm for 5 min to accelerate the separation of the micelles carrying the target analyte. The tubes were then stored in a refrigerator at 4.0 °C for approximately 10 min since decanting the formed mixed micelles from the sample solution (in the form of a cloud point) is easier at lower temperatures. The separated cloud point phase was subsequently dissolved in 500 μL of an EtOH: HNO₃ (5:1) solution prior to ICP-OES analysis. The concentration of Th(IV) remaining in the initial aqueous phase and in the cloud point phase was determined using ICP-OES. The following formula was applied to calculate the extraction efficiency (E, %).

$\mathrm{E}\left(\%\right)=\frac{\left[\mathrm{C}\right]\mathrm{o}-\left[\mathrm{C}\right]\mathrm{a}}{\left[\mathrm{C}\right]\mathrm{o}}\times 100$

In this formula, [C]a denotes the Th(IV) concentration in the liquid phase after separation was performed, while [C]o represents the original solution’s Th(IV) concentration.

2.4 Applications on real samples

2.4.1 Water samples

The applicability of the developed method was evaluated by monitoring Th(IV) concentrations in river water and seawater samples under optimized conditions. Since Th(IV) was not detected in the samples, all collected water samples were spiked with different concentrations of Th(IV). River and seawater samples were collected in pre-cleaned high density polyethylene (HDPE) bottles and acidified with 1.0% (v/v) HNO₃ after filtration through a 0.45-μm pore-size cellulose filter paper to remove suspended solid particles. Subsequently, 1.0% H₂O₂ and concentrated HNO₃ were added as oxidizing agents for organic materials in the collected water samples, and then the samples’ pH was brought to the ideal level using prepared buffer solutions to apply the above-described preconcentration CPE technique.

2.4.2 Soil samples/CRMs

An oven was used to dry the tested solid samples (soil or CRMs) to a consistent weight at 80 °C. Approximately 1.0 g of each sample was taken in a Teflon beaker 5.0 mL of pure HNO₃ was added and maintained at ambient temperature overnight. After almost 24 h, all samples were evaporated gradually to nearly complete dryness and then left to cool to room temperature. To ensure complete digestion, 1.5 mL of HClO₄ and 5.0 mL of concentrated HF were added to the samples and then dried at a moderate temperature. All samples were redissolved in 5.0 mL of 6.0 mol L⁻¹ HCl and then heated at 150 °C until the solution completely dried. Finally, all samples were dissolved in 5.0 mL of 1.0 mol L⁻¹ in enclosed beakers and heated to ensure the complete dissolution of samples. The resultant sample solutions were filtered and diluted to 100 mL with double-distilled water in a calibrated flask, after calibration at pH 3.0.

3 Results and discussion

3.1 Optimizing the proposed technique

3.1.1 Impact of the pH level

The pH of the sample solution was the first parameter optimized during the extraction process. pH plays a crucial role in controlling the chelation between metal ions and ligands and, consequently, can either facilitate or hinder the subsequent extraction of the target ions as chelates. In this study, Solochrome Cyanine R (SCR) was used as the selective chelator for Th(IV) in the microextraction process. Since the resulting complex requires a positively charged ion-pairing agent, cetyltrimethylammonium bromide (CTAB) was employed to promote the interaction between Th(IV) and SCR. This interaction led to the formation of a Th(IV)–SCR–CTAB complex, which is hydrophobic, insoluble in the aqueous phase, and can be easily extracted using an organic solvent. To confirm the selective separation of Th(IV) from certain lanthanide ions and U(VI), the effect of pH was investigated over the range of 2–7. As shown in Figure 2, the optimal extraction of the Th(IV)–SCR chelate occurred in a strongly acidic medium at pH ≥ 3.0. In contrast, the U(VI), Nd(III), Ce(III), and Gd(III)–SCR chelates began to be extracted in a weakly acidic medium at pH 5.5, reaching maximum extraction at pH 7. Previous studies reported the selective separation of Th(IV) from aqueous solutions containing various lanthanides using morin as the chelating agent in the pH range of 2.0–4.0 through a micelle-mediated process (Pawar et al., 2017). In the present work, this demonstrates that Th(IV) can be selectively separated from the tested solution at pH 3.0. Therefore, all subsequent experiments were performed at pH 3.

Figure 2

Figure 2. The impacts that pH has on Th(IV) ion separation, with Th(IV) (150 μg L⁻¹); CTAB (1.0 × 10⁻⁴ mol L⁻¹); KNO₃ (0.2 mol L⁻¹); SCR (1.0 × 10⁻⁴ mol L⁻¹); and Triton X-114 (0.24% w/v). Centrifugation time is 15 min and the temperature is 45 °C. A single standard deviation from three repeated sample measurements indicates an error.

3.1.2 The impacts of SCR concentration

SCR was chosen for this experiment because it forms a stable complex with Th(IV) in weakly acidic media rather than under basic conditions, thereby preventing the formation of hydroxides (Al-Mohaimeed et al., 2023; AlSalem et al., 2024). Figure 3 shows the effect of varying SCR concentrations on the efficiency of Th(IV) separation from the tested solutions. As illustrated, when the SCR concentration reached 0.8 × 10⁻⁴ mol L⁻¹, the extraction efficiency of the Th(IV)–SCR complex reached its maximum and remained constant at higher concentrations. At lower SCR concentrations, however, the extraction efficiency decreased significantly due to insufficient opportunities for chelation between Th(IV) ions and SCR molecules. Therefore, an SCR concentration of 0.8 × 10⁻⁴ mol L⁻¹ was selected for all subsequent experiments.

Figure 3

Figure 3. The impact of SCR concentration on Th(IV) separation with Th(IV) (100 μg L⁻¹); Triton X-114 (0.24% w/v); pH 3.0; CTAB (1.0 × 10⁻⁴ mol L⁻¹); and KNO₃ (0.2 mol L⁻¹). Centrifugation time of 15 min and a temperature of 45 °C. A single standard deviation from three repeated sample measurements indicates an error.

3.1.3 Effects of surfactant concentration

To arrange a successful mixed-MME process that can achieve the best and maximum efficiency of the separation process using the least volume of surfactants, optimizing the surfactant concentration has been considered a key factor. To specify the ideal concentration of the cationic and non-ionic surfactants, experimental tests were developed.

3.1.3.1 Effect of the Triton X-114 non-ionic surfactant concentration

In mixed-MME CPE experiments, the surfactant plays a critical role. To efficiently enrich target metal ions as hydrophobic complexes, a neutral or non-ionic surfactant is typically employed as the extracting agent (Mortada et al., 2021). In this study, Triton X-114 was selected as the non-ionic surfactant because of its favorable properties: a low cloud point temperature that allows phase separation at room temperature (30 °C), commercial availability, high density of the surfactant-rich phase, and relatively low toxicity at the concentrations required for sensitive determinations. Optimizing the surfactant concentration is essential to ensure effective separation of Th(IV). The addition of neutral Triton X-114 to the hydrophobic complex produced turbidity in the aqueous solution, resulting from the formation of small micelles that encapsulated the separated complex. This micelle formation facilitated the cloud point extraction process by enabling phase separation. The effect of Triton X-114 concentration on the extraction procedure was systematically examined. As shown in Figure 4b, increasing the concentration of Triton X-114 enhanced the extraction efficiency of the surfactant-rich phase, reaching a maximum at 0.24% (w/v). However, further increases in surfactant concentration led to reduced separation efficiency due to increased analyte volume and higher viscosity of the surfactant-rich phase. Therefore, the optimal concentration of Triton X-114 was determined to be 0.24% (w/v), as this value provided more consistent and reliable extraction results and increased extraction efficiency.

Figure 4

Figure 4. Effect of (a) CTAB concentration and (b) Triton X-114 concentration on the extraction of Th(IV) (Conditions: 150 μg L⁻¹ Th(IV), pH 3.0; 0.8 × 10⁻⁴ mol L⁻¹ SCR; 0.2 mol L⁻¹ KNO₃; 45 °C, with 15 minutes of centrifugation). A single standard deviation from three repeated sample measurements indicates an error.

3.1.3.2 Effect of changing the concentration of CTAB cationic surfactant

While maintaining the pH of the medium at a constant value, Triton X-114 concentration, and other experimental parameters, the effect of CTAB concentration on the extraction efficiency in the mixed-MME CPE experiments was evaluated over a wide range (0.2–5.0 × 10⁻⁴ mol L⁻¹). As shown in Figure 4a, the presence of the cationic surfactant (CTAB) significantly enhanced the extraction efficiency of the analyte ions, reaching a maximum at 1.0 × 10⁻⁴ mol L⁻¹ CTAB. This observation confirms that the Th(IV)–SCR–CTAB chelate is incorporated into the hydrophobic micellar core rather than remaining at the aqueous interface. However, at higher CTAB concentrations, an induced charge within the micelles may lead to electrostatic repulsion between them, increasing their hydrophilicity and consequently reducing extraction efficiency (Mortada et al., 2021). Therefore, for all subsequent experiments, a CTAB concentration of 1.0 × 10⁻⁴ mol L⁻¹ was selected.

3.1.4 The impacts of electrolyte and temperature

It has been previously noted that adding electrolytes to mixed surfactant systems can significantly accelerate micelle separation from the aqueous phase and lower the cloud point temperature, a phenomenon known as the salting-out effect (Mortada et al., 2021; Al-Mohaimeed et al., 2023; AlSalem et al., 2024). Salts enhance the attraction between ions in the hydrophilic regions of micelles, which promotes the precipitation of surfactant molecules. Therefore, the effects of various electrolytes, including KCl, KNO₃, KI, and Na₂SO₄, at concentrations ranging from 0.05–0.6 mol L⁻¹, were investigated at room temperature (25 °C) to improve mixed-MME separation and facilitate micelle phase separation at lower temperatures. Clouding was observed for all salts at room temperature, but KNO₃ provided the highest separation efficiency for Th(IV) ions. To further optimize conditions, different concentrations of KNO₃ (0.05–0.25 mol L⁻¹) were tested at temperatures between 35 and 50 °C. The results indicated that increasing KNO₃ concentration enhanced extraction efficiency, which reached 95% at 0.2 mol L⁻¹. This suggests that KNO₃ acts as a stabilizing shield, preserving micellar uniformity under acidic conditions, while increased ionic strength promotes complete phase separation (Basque et al., 2023). In addition, KNO₃ facilitated the transfer of the Th(IV)–SCR–CTAB complex from the aqueous phase into the surfactant-rich phase by enhancing its hydrophobicity. However, as shown in Figure 5, extraction efficiency decreased sharply at KNO₃ concentrations above 0.2 mol L⁻¹. Excess electrolyte disrupted phase separation by increasing the density of water droplets within the surfactant-rich phase (Mortada et al., 2021). Therefore, a KNO₃ concentration of 0.2 mol L⁻¹ was chosen for subsequent experiments. The effect of equilibration temperature was also examined within the range of 30–50 °C. The results showed that the extraction efficiency of the Th(IV)–SCR–CTAB complex remained stable between 40 and 50 °C. Consequently, 45 °C was selected as the optimal equilibration temperature. At higher temperatures, the complex began to degrade, ultimately reducing extraction efficiency.

Figure 5

Figure 5. The impacts of KNO₃ concentration on Th(IV) ion separation (150 μg L⁻¹ Th(IV), pH 3.0, 1.0 × 10⁻⁴ mol L⁻¹ SCR, 1.0 × 10⁻⁴ mol L⁻¹ CTAB, 0.24% w/v Triton X-114; and 10 min of centrifugation). A single standard deviation from three repeated sample measurements indicates an error.

3.1.5 Influence of extraction time and centrifugation period

In liquid–liquid microextraction procedures, the extraction time is defined as the interval between the addition of the electrolyte, which produces a cloudy solution, and the start of the centrifugation process (Mortada et al., 2021). In this study, the extraction time for mixed-MME CPE was evaluated within the range of 1–15 min. The results showed that maximum extraction efficiency was achieved in only 3 min, and longer extraction times had no noticeable effect. These findings are consistent with previously reported results (Al-Mohaimeed et al., 2023). Therefore, an extraction time of 3 min was selected to achieve maximum efficiency in the shortest duration. Centrifugation is also a critical step, as it reduces the time required to fully separate the surfactant-rich phase containing the target analyte. To determine the optimal centrifugation time, experiments were performed at 4,000 rpm for durations between 1 and 10 min. The results indicated that no significant improvement in separation efficiency was observed beyond 5 min. Consequently, all samples were centrifuged for 5 min in subsequent experiments to ensure complete phase separation.

3.1.6 Diluent impact

Several different solvents were investigated in this study to determine their ability to decrease the surfactant-rich phase’s viscosity produced following CPE. These solvents included ethanol, acetone, methanol, dimethyl sulfoxide, acetonitrile, and methyl isobutyl ketone, as shown in Table 2. The results indicate that surfactant-reach phases are highly soluble in methanol, so the volume of methanol is lower than the other solvents. Thus, the dilution solvent used throughout the experiments was methanol, with 500 μL being added. The planned CPE experiment was applied to determine the ideal preconcentration factor, which was found to be 100.

Table 2

Table 2. Effect of diluting agent type on preconcentration factors.

3.1.7 Interference studies

The effects that different anions and cations had on Th(IV) detection and CPE efficiency in real water and soil samples were examined in this study. Different concentrations of foreign ions were added to a 100 ng mL⁻¹ Th(IV) solution (see Table 3). Meanwhile, it is important to note that all samples were handled following the proposed CPE method. The point at which the separation and detection of Th(IV) have a relative error of less than ± 5.0% is known as the tolerance limit. Most coexisting ions examined in this study did not impact the detection and extraction of Th(IV). In fact, the results demonstrated that all the tested interfering ions did not form any stable complexes with SCR–CTAB at pH 3.0 following the formation of the binary complex Th(IV)/(III)/SCR/CTAB. Therefore, none of the examined coexisting ions affects Th(IV) extraction under optimal conditions. This implies that the solution’s pH level plays a vital role in regulating selectivity. The observed interferences of Zr⁴⁺, La³⁺, and Fe³⁺ can be attributed to their high charge density and strong complexation tendencies with the extracting ligand, which is particularly pronounced at the working pH. Zr⁴⁺ and Fe³⁺ undergo extensive hydrolysis, generating species that compete with Th(IV) for binding sites. Similarly, La³⁺ exhibits coordination behavior comparable to Th(IV), which resulted in a reduction in selectivity. To overcome this reduction, 500 μL of EDTA 0.1% (w/v) was employed as a masking agent since its stability constants with Zr⁴⁺ (log β = 45.9), La³⁺ (log β = 15.8), and Fe³⁺ (log β = 25.1) (Pawar et al., 2017; Perez-Tribouillier et al., 2019).

Table 3

Table 3. Separation of 10 μg L⁻¹ Th(IV) from different matrices.

3.1.8 Analytical characteristics

In the calibration graph, a linear relationship was observed between 0.4 and 50 ng mL⁻¹ after optimizing the Th(IV) pre-concentration. The linear regression equation for Th(IV) was $\mathrm{T}=1.65\mathrm{8C}–2.756\left({\mathrm{R}}^2=0.9981\right)$ , where T denotes intensity and C represents the Th(IV) concentration in solution (ng mL⁻¹).

Table 4 summarizes the analytical characteristics of the proposed CPE method, including the linear range, preconcentration factor, repeatability, regression equation, and detection and quantification limits.

Table 4

Table 4. The analytical characteristics and optimum conditions of the proposed method.

The limit of detection (LOD) is defined as the lowest analyte concentration that produces a measurable signal above the system’s noise level (Pawar et al., 2017), calculated as: CL = 3SB / m, where CL is the detection limit, SB is the standard deviation of the blank, and m is the slope of the calibration curve. Using this equation, the LOD was determined to be 0.8 ng mL⁻¹. The limit of quantification (LOQ), defined as CL = 10SB / m, was found to be 2.52 ng mL⁻¹, representing the lowest analyte concentration that can be quantified with acceptable accuracy. The preconcentration factor was calculated as 100 based on the determination of Th(IV) in 50 mL of sample solution by CPE, with a final volume of 0.5 mL after pre-concentration. For six replicate measurements of 10 ng mL⁻¹ Th(IV), the relative standard deviation (RSD) was 1.30%, demonstrating excellent precision.

3.2 Application studies

3.2.1 Applications to real samples

Several samples, including different water samples, have been analyzed to demonstrate the efficacy and reliability of the recommended methodology. Th(IV) was successfully measured in samples of wastewater, well water, tap water, seawater, and river water. The results are shown in Table 5. The range of recoveries for Th(IV) ions was 96.0 to 100.70%. These results clearly show that the proposed CPE technique is accurate and reliable.

Table 5

Table 5. Determination of Th(IV) concentrations in spiked samples following the suggested method.

3.2.2 The validation approach

In this experiment, IAEA Lake Sediment SL-1 and IAEA Soil-7, certified reference material (CRM), were examined to assess the accuracy of the established CPE method in identifying trace quantities of Th(IV). The documented-certified values and the analytical results for CRM appear to be in alignment (Table 6). The findings also showed that the principal matrix components of the standard materials under investigation did not interfere with the preconcentration technique that was developed for Th(IV). The data imply that the proposed method is accurate.

Table 6

Table 6. The detected concentrations of Th(IV) in the studied soil samples following separation by the proposed study.

3.3 Comparing the proposed methodology with others

The analytical performance of the present study was compared with previously reported pre-concentration methods for Th(IV), as summarized in Table 7. The comparison showed that, unlike some earlier approaches, the proposed method offers a lower detection limit and a wider dynamic analytical range (Constantinou and Pashalidis, 2011; Zolfonoun and Salahinejad, 2013; Basque et al., 2023). It is important to note, however, that the sample matrices used for extraction must be considered when evaluating different cloud point extraction (CPE) methods for Th(IV). The detection limits obtained with this method are comparable to those reported by other techniques. In addition, the mixed-MME approach developed in this study is faster to perform than many existing CPE methods for Th(IV) separation. The proposed method demonstrates several advantages, including low detection limits, a high enrichment factor (EF = 100), excellent accuracy, and the ability to induce clouding at relatively mild temperatures (see Table 4).

Table 7

Table 7. Comparison between the present study and previously reported studies about the separation and determination of Th(IV).

Compared with conventional techniques, this approach offers significant advantages in terms of lower operational cost, reduced chemical consumption, high reproducibility, and superior analytical performance, making it a promising tool for routine monitoring of thorium in environmental and industrial samples.

4 Conclusion

This study demonstrates that cloud point extraction using Triton X-114 and Solochrome Cyanine R provides a simple, accurate, and environmentally sustainable method for the selective separation and determination of Th(IV). The approach not only achieves high extraction efficiency and low detection limits but also reduces reliance on toxic organic solvents, aligning well with sustainable development principles. Beyond its analytical performance, the method offers clear advantages for routine monitoring of thorium in environmental, geological, and industrial samples, where sensitivity and selectivity are crucial. However, some limitations remain: the method requires controlled heating for cloud point formation, careful handling of matrix effects in highly complex samples, and additional steps for phase separation that may extend analysis time. Future studies may focus on extending the method to more complex matrices, adapting it into portable monitoring systems, or optimizing it with alternative ligands to enhance selectivity against competing ions. These aspects underline the potential of this method as a practical tool for both environmental safety assessment and nuclear industry applications.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, and further inquiries can be directed to the corresponding author/s.

Author contributions

YA: Conceptualization, Funding acquisition, Writing – original draft, Writing – review & editing. FA: Conceptualization, Methodology, Writing – original draft. AA: Investigation, Writing – original draft. MH: Conceptualization, Methodology, Writing – original draft. MW: Conceptualization, Data curation, Investigation, Writing – original draft, Writing – review & editing. MI: Formal analysis, Visualization, Writing – original draft. BK: Supervision, Writing – review & editing, Writing – original draft. AH-B: Funding acquisition, Supervision, Writing – original draft, Writing – review & editing.

Funding

The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported and funded by the Deanship of Scientific Research at Imam Mohammad Ibn Saud Islamic University (IMSIU) (grant number IMSIU-DDRSP2502).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The authors declare that no Gen AI was used in the creation of this manuscript.

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