Separation and preconcentration by cloud point extraction procedures for determination of ions: recent trends and applications

Major and Trace Airborne Elements and Ecological Risk Assessment: Georgia Moss Survey 2019-2023

The study, carried out as part of the International Cooperative Program on Effects of Air Pollution on Natural Vegetation and Crops, involved collecting 95 moss samples across the territory of Georgia during the period from 2019 to 2023. Primarily samples of Hypnum cupressiforme were selected, with supplementary samples of Abietinella abietina, Pleurozium schreberi, and Hylocomium splendens in cases of the former's absence. The content of 14 elements (Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, S, Sr, V, and Zn) was detected using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), while the Hg content was determined using a Direct Mercury Analyzer. To identify any relationships between chemical elements and to depict their sources, multivariate statistics was applied. Principal component analysis identified three main components: PC1 (geogenic, 43.4%), PC2 (anthropogenic, 13.3%), and PC3 (local anomalies, 8.5%). The results were compared with the first moss survey conducted in Georgia in the period from 2014 to 2017, offering insights into temporal trends of air quality. Utilizing GIS, a spatial map illustrating pollution levels across Georgia, based on the Pollution Load Index, was generated. The Potential Environmental Risk Index emphasized significant risks associated with mercury and cadmium at several locations. The study highlights the utility of moss biomonitoring in assessing air pollution and identifying hotspots of contamination. The findings from this study could be beneficial for future biomonitoring research in areas with varying physical and geographical conditions.

Improvement in the Chromium(VI)-Diphenylcarbazide Determination Using Cloud Point Microextraction; Speciation of Chromium at Low Levels in Water Samples

A reliable, rapid, and low-cost procedure for determining very low concentrations of hexavalent chromium (Cr) in water is discussed. The procedure is based in the classical reaction of Cr6+ with diphenylcarbazide. Once this reaction has taken place, sodium dodecylsulfate is added to obtain an ion-pair, and Triton X-114 is incorporated. Next, the heating of the mixture allows two phases that can be separated by centrifugation to be obtained in a cloud point microextraction (CPE) process. The coacervate contains all the Cr6+ originally present in the water sample, so that the measurement by molecular absorption spectrophotometry allows the concentration of the metal to be calculated. No harmful organic solvents are required. The discrimination of hexavalent and trivalent forms is achieved by including an oxidation stage with Ce4+. To take full advantage of the pre-concentration effect inherent to the coacervation process, as well as to minimize reagent consumption and waste generation, a portable mini-spectrophotometer which is compatible with microvolumes of liquid samples is used. The preconcentration factor is 415 and a chromium concentration as low as 0.02 µg L-1 can be detected. The procedure shows a good reproducibility (relative standard deviation close to 3%).

A rapid room-temperature cloud point extraction for spectrophotometric determination of Copper (II) with 6,7-dihydroxy-2,4-diphenylbenzopyrylium chloride

The conditions for the surfactant rich phase of Triton X-100 formation and the extraction of Copper (II) as a complex with 6,7-dihydroxy-2,4-diphenylbenzopyrylium chloride at room temperature have been optimized. It was shown that the sodium salt of p-toluic acid can be used as a chemical initiator of cloud point extraction. The optimal conditions for room temperature cloud point extraction were found to be: pH 5.0; 1 v/v.% Triton X-100; 3.75·10^-2 M sodium salt of p-toluic acid and the addition of 0.5 M H₂SO₄ solution to pH 5.0. The formation of the surfactant rich phase begins instantly. The 2-propanol was proposed as a diluent for the surfactant rich phase. The calibration graph is linear in the range of Copper (II) concentrations of 6-870 μg/L, and the limit of detection and limit of determination are 1.8 and 6 μg/L, respectively. The proposed method was successfully applied for the spectrophotometric determination of Copper (II) in water samples with a relative standard deviation not exceeding 4.5%.

Determination of ultra-trace levels of palladium in water samples by cloud point extraction and graphite furnace atomic absorption spectrometry

A highly sensitive method for the determination of ultra-trace levels of palladium in water samples by cloud point extraction and graphite furnace atomic absorption spectrometry is developed. The procedure is based on complexation of palladium with a laboratory-prepared novel chelating agent, 2-(5-bromo-4-methyl-2-pyridylazo)-5-dimethylaminoaniline (5-Br-4-CH3-PADMA) and subsequent micelle-mediated extraction of the product using the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) as an extracting agent. Analytical parameters affecting the separation and detection process, such as pH, concentration of the chelating agent and surfactant, equilibration temperature, and time are investigated. The optimized conditions are as follows: pH 6.0 HAc–NaAc buffer solution, 1 × 10−5 mol L−1 5-Br-4-CH3-PADMA, and 0.1% (w/v) Triton X-114. Under the optimized conditions, the calibration graph is linear in the range of 0.1–12 ng/mL, the detection limit is 0.05 ng/mL for palladium, and the relative standard deviation is 2.9% ( c = 1.0 ng/mL, n = 10). The enrichment factor, defined as the ratio of the aqueous solution volume to that of the surfactant-rich phase volume after dilution with HNO3–methanol solution, is 200. The proposed method is applied to the determination of palladium in water samples with satisfactory results.

Preparation of environmental samples for chemical speciation of metal/metalloids: A review of extraction techniques

Chemical speciation is a relevant topic in environmental chemistry since the (eco)toxicity, bio (geo)chemical cycles, and mobility of a given element depend on its chemical forms (oxidation state, organic ligands, etc.). Maintaining the chemical stability of the species and avoiding equilibrium disruptions during the sample treatment is one of the biggest challenges in chemical speciation, especially in environmental matrices where the level of concomitants/interferents is normally high. To achieve this task, strategies based on chemical properties of the species can be carried out and pre-concentration techniques are often needed due to the low concentration ranges of many species (μg L^-1 - ng L^-1). Due to the significance of the topic and the lack of reviews dealing with sample preparation of metal (loid)s (usually, sample preparation reviews focus on the total metal content), this work is presented. This review gives an up-to-date overview of the most common sample preparation techniques for environmental samples (water, soil, and sediments), with a focus on speciation of metal/metalloids and determination by spectrometric techniques. Description of the methods is given, and the most recent applications (last 10 years) are presented.

Determination of polonium-210 in environmental samples using diglycolamide-based cloud point extraction coupled to alpha spectrometry analysis

This study presents a novel cloud point extraction (CPE) methodology for the separation and enrichment of polonium-210 prior to alpha-spectrometric quantification in water, urine and digested samples. The extractive behaviour of diglycolamide-based ligands towards Po by CPE was determined and optimised in various acidic conditions. The extraction efficiency and selectivity of the CPE systems depend greatly on the choice of the extracting agent and acidic conditions. The thorough optimisation of those specific parameters has led to the development of a suitable cloud point extraction system for the determination of polonium-210 at ultra-trace levels compatible with alpha-spectrometry. To facilitate this coupling, a back-extraction procedure was optimised and performed on the surfactant-rich phase to enable the spontaneous deposition of polonium-210 onto a silver disk; this also avoids making the matrix transfer step mandatory due to the presence of a nitric medium. Method detection and quantification limits of 3.5 and 12 mBq L^-1, respectively, were determined by alpha spectrometry. The robustness of the proposed methodology was demonstrated by the determination of polonium ions concentration in various environmental and biological samples and solid certified reference materials.

3D Nanoarchitecture of Polyaniline-MoS2 Hybrid Material for Hg(II) Adsorption Properties

We report the facile hydrothermal synthesis of polyaniline (PANI)-modified molybdenum disulfide (MoS2) nanosheets to fabricate a novel organic-inorganic hybrid material. The prepared 3D nanomaterial was characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction studies. The results indicate the successful synthesis of PANI-MoS2 hybrid material. The PANI-MoS2 was used to study the extraction and preconcentration of trace mercury ions. The experimental conditions were optimized systematically, and the data shows a good Hg(II) adsorption capacity of 240.0 mg g-1 of material. The adsorption of Hg(II) on PANI-MoS2 hybrid material may be attributed to the selective complexation between the-S ion of PANI-MoS2 with Hg(II). The proposed method shows a high preconcentration limit of 0.31 µg L-1 with a preconcentration factor of 640. The lowest trace Hg(II) concentration, which was quantitatively analyzed by the proposed method, was 0.03 µg L-1. The standard reference material was analyzed to determine the concentration of Hg(II) to validate the proposed methodology. Good agreement between the certified and observed values indicates the applicability of the developed method for Hg(II) analysis in real samples. The study suggests that the PANI-MoS2 hybrid material can be used for trace Hg(II) analyses for environmental water monitoring.

Natural TiO2-Nanoparticles in Soils: A Review on Current and Potential Extraction Methods

The monitoring of anthropogenic TiO2-nanoparticles in soils is challenged by the knowledge gap on their characteristics of the large natural TiO2-nanoparticle pool. Currently, no efficient method is available for characterizing natural TiO2-nanoparticles in soils without an extraction procedure. Considering the reported diversity of extraction methods, the following article reviews and discusses their potential for TiO2 from soils, focusing on the selectivity and the applicability to complex samples. It is imperative to develop a preparative step reducing analytical interferences and producing a stable colloidal dispersion. It is suggested that an oxidative treatment, followed by alkaline conditioning and the application of dispersive agents, achieve such task. This enables the further separation and characterization through size or surface-based separation (i.e., hydrodynamic fractionation methods, filtration or sequential centrifugation). Meanwhile, cloud point extraction, gel electrophoresis, and electrophoretic deposition have been studied on various nanoparticles but not on TiO2-nanoparticles. Furthermore, industrially applied methods in, for example, kaolin processing (flotation and flocculation) are interesting but require further improvements on terms of selectivity and applicability to soil samples. Overall, none of the current extraction methods is sufficient toward TiO2; however, further optimization or combination of orthogonal techniques could help reaching a fair selectivity toward TiO2.

Fast room temperature cloud point extraction procedure for spectrophotometric determination of phosphate in water samples

A novel fast room temperature cloud point extraction (RT-CPE) procedure for preconcentration and spectrophotometric determination of phosphate based on the heteropoly blue formation was developed. The proposed method includes the formation of yellow molybdoantymonatophosphoric heteropoly complex, its extraction into Triton X-100 micellar phase obtained at room temperature and reduction of heteropoly complex by ascorbic acid solution in ethanol and absorbance measurement of heteropoly blue at 790 nm. Under optimal conditions (1% (v/v) of Triton X-100 and 0.05 M of ammonium benzoate for initiating of RT-CPE; 0.13 M ethanolic solution of ascorbic acid for reduction of heteropoly complex and dilution of surfactant rich phase), the calibration graph is linear in the range of phosphate concentrations of 1.58-63 μg L^-1. The proposed RT-CPE procedure has been successfully applied to preconcentration phosphates and its spectrophotometric determination in water samples.

Effect of different operating conditions in cloud point assisted extraction of thymol from Ajwain (Trachyspermum Ammi L.) seeds and recovery using solvent

Cloud point assisted extraction of thymol from water extract of Ajwain (Trachyspermum Ammi L.) seeds has been reported. Effects of different operating conditions, i.e., concentration of surfactant, heating time and temperature in extraction efficiency were investigated. It was observed that maximum extraction efficiency of thymol was achieved with 30% (v/v) of SPAN 80 surfactant, 45 min of heating at 65 °C. Recovery of thymol from the surfactant complex was optimal at 1:3 coacervate phase to solvent (acetone) volume ratio. A semi-empirical correlation was proposed at the optimum time to predict the concentration of surfactant and temperature required for a desired yield.

Determination of Pb in environmental samples after cloud point extraction using crown ether

In the present study, a new cloud point extraction methodology based on the selective preconcentration and the extraction of stable lead in acidic conditions with 4',4''(5'')-di-tert-butyldicyclohexano-18-crown-6 as a chelating agent was developed, optimized and validated. A mixture of Triton X-114 as non-ionic surfactant and CTAB as cationic surfactant was used to produce micellar structures that incorporate the chelating agent. Phase separation, induced by coacervation, was achieved by increasing the temperature of the system above the cloud point temperature. Pb extraction efficiency was maximized through an optimisation process where the effect of each parameter (i.e. non-ionic and ionic surfactant concentrations, pH, chelating agent concentration and cloud point temperature) on the chemical recoveries of Pb was assessed. Under optimum experimental conditions, the method reaches recoveries greater than 67% for Pb in a variety of complex matrices. In order to facilitate the quantification of Pb by plasma based instrumentations, a back-extraction procedure using aqueous solution of ammonium citrate were performed on the surfactant rich phase in order to reduce the effects on sample introduction and non-spectral interferences. LOD and LOQ of 0.8µgL^-1 and 2.6µgL^-1, respectively, were determined by ICP-OES for the complete procedure. Using the back-extraction approach, a preconcentration factor of 39 was achieved for an initial sample volume of 195mL. The ruggedness of the methodology was validated by determining Pb concentration in various environmental and biological samples.

Determination of Ultra-trace Rhodium in Water Samples by Graphite Furnace Atomic Absorption Spectrometry after Cloud Point Extraction Using 2-(5-Iodo-2-Pyridylazo)-5-Dimethylaminoaniline as a Chelating Agent

A highly sensitive method based on cloud point extraction (CPE) separation/preconcentration and graphite furnace atomic absorption spectrometry (GFAAS) detection has been developed for the determination of ultra-trace amounts of rhodium in water samples. A new reagent, 2-(5-iodo-2-pyridylazo)-5-dimethylaminoaniline (5-I-PADMA), was used as the chelating agent and the nonionic surfactant TritonX-114 was chosen as extractant. In a HAc-NaAc buffer solution at pH 5.5, Rh(III) reacts with 5-I-PADMA to form a stable chelate by heating in a boiling water bath for 10 min. Subsequently, the chelate is extracted into the surfactant phase and separated from bulk water. The factors affecting CPE were investigated. Under the optimized conditions, the calibration graph was linear in the range of 0.1–6.0 ng/mL, the detection limit was 0.023 ng/mL for rhodium and relative standard deviation was 3.67% (c = 1.0 ng/mL, n = 11)．The method has been applied to the determination of trace rhodium in water samples with satisfactory results

Metal and Metalloid Size-Fractionation Strategies in Spatial High-Resolution Sediment Pore Water Profiles

Sediment water interfaces (SWIs) are often characterized by steep biogeochemical gradients determining the fate of inorganic and organic substances. Important transport processes at the SWI are sedimentation and resuspension of particulate matter and fluxes of dissolved materials. A microprofiling and micro sampling system (missy), enabling high resolution measurements of sediment parameters in parallel to a direct sampling of sediment pore waters (SPWs), was combined with two fractionation approaches (ultrafiltration (UF) and cloud point extraction (CPE)) to differentiate between colloidal and dissolved fractions at a millimeter scale. An inductively coupled plasma-quadrupole mass spectrometry method established for volumes of 300 μL enabled the combination of the high resolution fractionation with multi-element analyzes. UF and CPE comparably indicated that manganese is predominantly present in dissolved fractions of SPW profiles. Differences found for cobalt and iron showed that the results obtained by size-dependent UF and micelle-mediated CPE do not necessarily coincide, probably due to different fractionation mechanisms. Both methods were identified as suitable for investigating fraction-related element concentrations in SPW along sediment depth profiles at a millimeter scale. The two approaches are discussed with regard to their advantages, limitations, potential sources of errors, further improvements, and potential future applications.

Application of Micro-cloud point extraction for spectrophotometric determination of Malachite green, Crystal violet and Rhodamine B in aqueous samples

A novel, green, simple and fast method was developed for spectrophotometric determination of Malachite green, Crystal violet, and Rhodamine B in water samples based on Micro-cloud Point extraction (MCPE) at room temperature. This is the first report on the application of MCPE on dyes. In this method, to reach the cloud point at room temperature, the MCPE procedure was carried out in brine using Triton X-114 as a non-ionic surfactant. The factors influencing the extraction efficiency were investigated and optimized. Under the optimized condition, calibration curves were found to be linear in the concentration range of 0.06-0.60mg/L, 0.10-0.80mg/L, and 0.03-0.30mg/L with the enrichment factors of 29.26, 85.47 and 28.36, respectively for Malachite green, Crystal violet, and Rhodamine B. Limit of detections were between 2.2 and 5.1μg/L.

Considerations of Environmentally Relevant Test Conditions for Improved Evaluation of Ecological Hazards of Engineered Nanomaterials

Engineered nanomaterials (ENMs) are increasingly entering the environment with uncertain consequences including potential ecological effects. Various research communities view differently whether ecotoxicological testing of ENMs should be conducted using environmentally relevant concentrations-where observing outcomes is difficult-versus higher ENM doses, where responses are observable. What exposure conditions are typically used in assessing ENM hazards to populations? What conditions are used to test ecosystem-scale hazards? What is known regarding actual ENMs in the environment, via measurements or modeling simulations? How should exposure conditions, ENM transformation, dose, and body burden be used in interpreting biological and computational findings for assessing risks? These questions were addressed in the context of this critical review. As a result, three main recommendations emerged. First, researchers should improve ecotoxicology of ENMs by choosing test end points, duration, and study conditions-including ENM test concentrations-that align with realistic exposure scenarios. Second, testing should proceed via tiers with iterative feedback that informs experiments at other levels of biological organization. Finally, environmental realism in ENM hazard assessments should involve greater coordination among ENM quantitative analysts, exposure modelers, and ecotoxicologists, across government, industry, and academia.

Development of cloud-point extraction method for preconcentration of trace quantities of cobalt and nickel in water and food samples

A new, efficient, and sensitive cloud point methodology was developed for preconcentration of trace quantities of cobalt and nickel in water and food samples.

Extraction and pre-concentration of platinum and palladium from microwave-digested road dust via ion exchanging mesoporous silica microparticles prior to their quantification by quadrupole ICP-MS

We report on the use of mesoporous silica microparticles (μPs) functionalized with quarternary amino groups for the isolation of platinum and palladium tetrachloro complexes from aqueous road dust digests. The μPs have a size ranging from 450 to 850 nm and are suspended directly in the aqueous digests, upon which the anionic Pt and Pd complexes are retained on the cationic surface. Subsequently, the μPs are separated by centrifugation. Elements that cause spectral interferences in ICP-MS determination of Pt and Pd can be quantitatively removed by adding fresh 0.240 mol L⁻¹ HCl to the μPs and by repeating the centrifugation step. The analyte-loaded μPs are then dissolved in 0.1 mL of 2 mol L⁻¹ HF, diluted to 2 mL, and the solutions thus obtained are analyzed by quadrupole ICP-MS. This method avoids analyte elution from the sorbent. This “dispersed particle extraction” approach yielded a run-to-run relative standard deviation ≤ 5 % for Pt and ≤ 4 % for Pd (at 0.1 ng mL⁻¹, n = 4 road dust digests). Method detection limits (expressed as concentrations in the dust samples) are 2 and 1 ng g⁻¹ for Pt and Pd, respectively. The method was validated by analysis of a reference material (BCR CRM 723) and applied to the analysis of road dust samples collected in downtown Vienna. Pt and Pd concentrations in samples collected in summer and in winter were compared, with concentrations ranging from 205 to 1445 ng g⁻¹ for Pt and from 201 to 1230 ng g⁻¹ for Pd.

Graphical Abstract

Cloud point extraction, preconcentration and spectrophotometric determination of trace amount of manganese(II) in water and food samples

A new cloud point extraction (CPE) process using the nonionic surfactant Triton X-114 to extract manganese(II) from aqueous solution was investigated. The method is based on the complexation reaction of manganese(II) with 1,2,5,8-tetrahydroxyanthracene-9,10-dione (quinalizarin) in the presence of borate buffer at pH 8.5 and micelle-mediated extraction of the complex. The enriched analyte in the surfactant-rich phase was determined by spectrophotometry at 528nm. The optimal extraction and reaction conditions (e.g. pH, reagent and surfactant concentrations, temperature and centrifugation times) were evaluated and optimized. Under the optimized experimental conditions, the analytical characteristics of the method (e.g., limit of detection (LOD), linear range, preconcentration and improvement factors) were obtained. The proposed CPE method showed linear calibration within the range 5.0-200ngmL(-1) of manganese(II) and the limit of detection of the method was 0.8ngmL(-1) with an preconcentration factor of ∼50 when 25mL of sample solution was preconcentrated to 0.5mL. The relative standard deviation (RSD) and relative error were found to be 1.35% and 1.42%, respectively (CMn(II)=150ngmL(-1), n=6) for pure standard solutions. The interference effect of some cations and anions was also studied. In the presence of foreign ions, no significant interference was observed. The method was applied to the determination of manganese(II) in water and food samples with a recovery for the spiked samples in the range of 95.87-102.5%.

A green and efficient procedure for the preconcentration and determination of cadmium, nickel and zinc from freshwater, hemodialysis solutions and tuna fish samples by cloud point extraction and flame atomic absorption spectrometry

Cloud point extraction (CPE) was used to simultaneously preconcentrate trace-level cadmium, nickel and zinc for determination by flame atomic absorption spectrometry (FAAS). 1-(2-Pyridilazo)-2-naphthol (PAN) was used as a complexing agent, and the metal complexes were extracted from the aqueous phase by the surfactant Triton X-114 ((1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol). Under optimized complexation and extraction conditions, the limits of detection were 0.37μgL(-1) (Cd), 2.6μgL(-1) (Ni) and 2.3μgL(-1) (Zn). This extraction was quantitative with a preconcentration factor of 30 and enrichment factor estimated to be 42, 40 and 43, respectively. The method was applied to different complex samples, and the accuracy was evaluated by analyzing a water standard reference material (NIST SRM 1643e), yielding results in agreement with the certified values.