Cloud Point Extraction Method Research Articles

Determination of Cr(III) and total chromium in water samples by cloud point extraction and flame atomic absorption spectrometry

A sensitive and selective method has been developed for the speciation of chromium in water samples based on cloud point extraction (CPE) separation and preconcentration and determination by flame atomic absorption spectrometry. In the CPE method, Cr(III) reacts with acetylacetone yielding a hydrophobic complex, which is entrapped in the Triton X-100 surfactant-rich phase, whereas Cr(VI) remained in aqueous phase. Thus, separation of Cr(III) and Cr(VI) could be realized. Total chromium was determined after the reduction of Cr(VI) to Cr(III) by using ascorbic acid as reducing reagent. Under the optimal conditions, the detection limit of this method for Cr(III) was 0.32 ng mL−1 with an enrichment factor of 35, and the relative standard deviation was 3.4% (c = 100 ng mL−1, n = 7). The method has been applied to the speciation of chromium in natural water samples with satisfactory results.

Simultaneous preconcentration and determination of U(VI), Th(IV), Zr(IV) and Hf(IV) ions in aqueous samples using micelle-mediated extraction coupled to inductively coupled plasma-optical emission spectrometry

A simple cloud point extraction method followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed for simultaneous preconcentration and determination of trace amounts of U(VI), Th(IV), Zr(IV) and Hf(IV) ions in aqueous samples. The metal ions in 50 ml of aqueous solution (containing 0.1 M sodium acetate, pH 6.0) were formed complexes with dibenzoylmethane (DBM). Then, Triton X-114 (0.2%, w/v) was added to the solution. By increasing the temperature of the solution up to 50 °C, a phase separation occurred. After centrifugation at 4000 rpm for 6 min, the surfactant-rich phase (sediment phase) was diluted with 1.0 ml of 20:80 (v/v) of methanol/1 M HNO 3. The metal ions were then determined using ICP-OES. Finally, the main factors affecting the cloud point extraction were evaluated and optimized. Under optimized conditions, enhancement factors in the range of 37.0–43.6 were obtained. The calibration graphs were linear in the range of 0.5–1500 μg l −1 for Th and Zr, 0.5–500 μg l −1 for Hf and 2.5–1240 μg l −1 for U with correlation coefficients ( r 2) better than 0.9926. The detection limits were between 0.1 and 1.0 μg l −1 and the R.S.D. values for seven replicates were lower than 6.1%.

Development of a cloud-point extraction method for copper and nickel determination in food samples

A new, simple and versatile cloud-point extraction (CPE) methodology has been developed for the separation and preconcentration of copper and nickel. The metals in the initial aqueous solution were complexed with 2-(2′-benzothiazolylazo)-5-( N, N-diethyl)aminophenol (BDAP) and Triton X-114 was added as surfactant. Dilution of the surfactant-rich phase with acidified methanol was performed after phase separation, and the copper and nickel contents were measured by flame atomic absorption spectrometry. The variables affecting the cloud-point extraction were optimized using a Box–Behnken design. Under the optimum experimental conditions, enrichment factors of 29 and 25 were achieved for copper and nickel, respectively. The accuracy of the method was evaluated and confirmed by analysis of the followings certified reference materials: Apple Leaves, Spinach Leaves and Tomato Leaves. The limits of detection expressed to solid sample analysis were 0.1 μg g −1 (Cu) and 0.4 μg g −1 (Ni). The precision for 10 replicate measurements of 75 μg L −1 Cu or Ni was 6.4 and 1.0, respectively. The method has been successfully applied to the analysis of food samples.

Determination of trace aluminum in biological and water samples by cloud point extraction preconcentration and graphite furnace atomic absorption spectrometry detection

A cloud point extraction (CPE) method for the preconcentration of trace aluminum prior to its determination by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. The CPE method is based on the complex of Al(III) with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP), and then entrapped in non-ionic surfactant Triton X-114. PMBP was used not only as chelating reagent in CPE preconcentration, but also as chemical modifier in GFAAS determination. The main factors affecting CPE efficiency, such as pH of sample solution, concentration of PMBP and Triton X-114, equilibration temperature and time, were investigated in detail. An enrichment factor of 37 was obtained for the preconcentration of Al(III) with 10 mL solution. Under the optimal conditions, the detection limit of this method for Al(III) is 0.09 ng mL −1, and the relative standard deviation is 4.7% at 10 ng mL −1 Al(III) level ( n = 7). The proposed method has been applied for determination of trace amount of aluminum in biological and water samples with satisfactory results.

Fiber optic-linear array detection spectrophotometry in combination with cloud point extraction for simultaneous preconcentration and determination of cobalt and nickel

A new combined method including fiber optic-linear array detection spectrophotometry (FO-LADS) and cloud point extraction (CPE) was developed using a cylindrical micro cell for simultaneous preconcentration and determination of different species. The CPE and FO-LADS methods have good matching conditions for combination because FO-LADS is suitable as a detection technique for the low volume of remained phase obtained after CPE. This combination was carried out using 50 μL cylindrical micro cell and then employed for simultaneous preconcentration and determination of cobalt and nickel. Cloud point extraction method was based on the chromogenic reaction of metal ions and 1-(2-pyridylazo)-2-naphthol (PAN) and then preconcentration of formed complexes using octylphenoxypolyethoxyethanol (Triton X-114). The remained phase after CPE was transferred into cylindrical micro cell and located at the cell holder of FO-LADS. The spectra of cobalt and nickel complexes were collected by FO-LADS and processed for ordinary and first derivative spectrophotometry. Optimization of different parameters was evaluated. Under optimum conditions, calibration curves were linear in the range of 0.6–30.0 and 0.1–15.0 μg L −1 with detection limits of 0.2 and 0.04 μg L −1 for Co and Ni respectively. The relative standard deviations (R.S.D.s) were lower than 4%. The obtained enhancement factors were 198 and 199 for cobalt and nickel, respectively. The proposed method was compared with the other methods and applied to the analysis of several real and spiked samples.

Laser induced-thermal lens spectrometry after cloud point extraction for the determination of trace amounts of rhodium

A new combination method, employing thermal lens spectrometry (TLS) after cloud point extraction (CPE), has been developed for the preconcentration and determination of rhodium. TLS and CPE methods have good matching conditions for the combination because TLS is a suitable method for the analysis of low volume samples obtained after CPE. Rhodium was complexed with 1-(2-pyridylazo)-2-naphthol (PAN) as a complexing agent in an aqueous medium and concentrated by octylphenoxypolyethoxyethanol (Triton X-114) as a surfactant. After the phase separation at 50 °C based on the cloud point extraction of the mixture, the surfactant-rich phase was dried and the remaining phase was dissolved using 20 μL of carbon tetrachloride. The obtained solution was introduced into a quartz micro cell and the analyte was determined by laser induced-thermal lens spectrometry (LI-TLS). The single laser TLS was used as a sensitive method for the determination of Rhodium-PAN complex in 20 μL of the sample. Under optimum conditions, the analytical curve was linear for the concentration range of 0.5–50 ng mL −1 and the detection limit was 0.06 ng mL −1. The enhancement factor of 450 was achieved for 10 mL samples containing the analyte and relative standard deviations were lower than 5%. The developed method was successfully applied to the extraction and determination of rhodium in water samples.

Cloud point extraction applied to casein proteins of cow milk and their identification by mass spectrometry

This work describes the optimization of a cloud point extraction (CPE) method for casein proteins from cow milk samples. To promote phase separation, polyoxyethylene(8) isooctylphenyl ether (Triton ® X-114) and sodium chloride (NaCl) were used as nonionic surfactant and electrolyte, respectively. Using multivariate studies, four major CPE variables were evaluated: Triton ® X-114 concentration, sample volume, NaCl concentration, and pH. The results show that surfactant concentration and sample volume were the main variable affecting the CPE process, with the following optimized parameters: 1% (w/v) Triton ® X-114 concentration, 50 μL of sample volume, 6% (w/v) NaCl concentration and extractions carried out at pH 7.0. At these conditions, 923 ± 66 and 67 ± 2 μg mL −1 of total protein were found in the surfactant-rich and surfactant-poor phases, respectively. Finally, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) was then used to evaluate those target proteins (α s1-casein, α s2-casein and β-casein) separation as well as to check the efficiency of the extraction procedure, making a fingerprint of those target proteins possible.

Simplified cloud point extraction for the preconcentration of ultra-trace amounts of gold prior to determination by electrothermal atomic absorption spectrometry

A simple and sensitive cloud point extraction method has been developed for the preconcentration of ultra-trace amounts of gold as a prior step to its determination by electrothermal atomic absorption spectrometry. It is based on the extraction of gold in hydrochloric acid medium using the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) without adding a chelating agent. The preconcentration of a 50 mL sample solution was thus enhanced by a factor of 200. The resulting calibration graph was linear in the range of 10–200 ng L−1 with a correlation coefficient of 0.9993. The limit of detection (3s) obtained under optimal conditions was 2.0 ng L−1. The relative standard deviation for 10 replicate determinations at a 100 ng L−1 Au level was 3.6%. The method was applied to the ultra-trace determination of gold in water and copper samples.

Highly selective determination of trace quantities of mercury in water samples after preconcentration by the cloud-point extraction method

A cloud-point extraction method for preconcentration of ultra-trace quantities of mercury ions as a prior step to its determination by spectrophotometry. The method is based on the cloud-point extraction of mercury in iodide media with Triton X-114. The preconcentrated mercury was then determined spectrophotometrically by measuring the absorbance of the surfactant rich phase at 300 nm and also by cold-vapour atomic absorption spectrometry (CVAAS). Linearity was obeyed in the range of 0.40–40.0 ng mL−1 by CVAAS and in the range of 10.0–400.0 ng mL−1 by spectrophotometry. The detection limit is 3.0 ng mL−1 by spectrophotometry and 0.10 ng mL−1 by CVAAS. The interference effect of several anions and cations was also tested. The method was used to determine mercury in water samples.

Cloud Point Extraction and Preconcentration for the Determination of Cu and Ni in Natural Water by Flame Atomic Absorption Spectrometry

In this work, a new cloud point extraction (CPE) method was developed for the separation and preconcentration of copper and nickel. The analyte was complexed with 3‐[(8‐{[(E)‐2‐hydroxyimino‐1‐methylpropylidene] amino}‐1‐naphthyl) imino]‐2‐butanone oxime (H2mdo) in the initial aqueous solution and octylphenoxy polyethoxy ethanol (Triton X‐114) was added as a surfactant. After phase separation, based on the cloud point in the mixture, and dilution of the surfactant‐rich phase with methanol containing 0.1 mol l−1 HNO3, the enriched analytes were determined by flame atomic absorption spectrometry. After optimization of the complexation and extraction conditions (i.e. pH=8.5, H2mdo=3×10−4 mol l−1, Triton X‐114=0.1% (w/v)) the enhancement factors of 65 and 59 and detection limits of 0.14 and 0.2 ng ml−1 were obtained for copper and nickel respectively. The proposed method was applied to the determination of copper and nickel in several natural water samples with satisfactory results.

Development of a cloud point extraction and preconcentration method for silver prior to flame atomic absorption spectrometry

The possibility was investigated of using 2-mercaptobenzothiazole (MBT) for Ag(I) concentration by micellar extraction at cloud point (CP) temperature and subsequent determination by flame atomic absorption spectrometry (FAAS). The method is based on the complexation of Ag(I) with 2-mercaptobenzothiazole (MBT) in the presence of non-ionic micelles of Triton X-114. The effect of experimental conditions such as pH, concentration of chelating agent and surfactant, equilibration temperature and time on cloud point extraction was studied. Under the optimum conditions, the preconcentration of 10 mL of water sample in the presence of 0.1% Triton X-114 and 2 × 10−4 mol L−1 2-mercaptobenzothiazole permitted the detection of 2.2 ng mL−1 silver. The calibration graph was linear in the range of 10–200 ng mL−1, and the recovery of more than 99% was achieved. The proposed method was used in FAAS determination of Ag(I) in water samples.

Laser induced thermal lens spectrometry for cobalt determination after cloud point extraction

A new approach, employing cloud point extraction (CPE) in combination with thermal lens spectrometry (TLS), has been developed for the determination of cobalt. The CPE and TLS methods have good matching conditions for combination because TLS is suitable for low volume samples obtained after CPE and for organic solvents, which are used for dissolving the remaining analyte phase. 1-(2-Pyridylazo)-2-naphthol (PAN) was used as a complexing agent and octylphenoxypolyethoxyethanol (Triton X-114) was added as a surfactant; then the pH of solution was adjusted. After phase separation at 50 °C based on the cloud point extraction of the mixture, the surfactant-rich phase was dried and the remaining phase was dissolved using 20 μL of carbon tetrachloride. The obtained solution was introduced into the quartz micro cell and the analyte was determined by thermal lens spectrometry. The He–Ne laser (632.8 nm) was used as both the probe and the excite source. Under optimum conditions, the analytical curve was linear for the concentration range of 0.2–40 ng mL −1 and the detection limit was 0.03 ng mL −1. The enhancement factor of 470 was achieved for a 10 mL sample. Relative standard deviations were lower than 5%. The method was successfully applied to the extraction and determination of cobalt in tap, river and sea water.

SELECTIVE CLOUD POINT EXTRACTION AND PRECONCENTRATION OF COPPER BY THE USE OF DITHIZONE AS A COMPLEXING AGENT

The aim of this work was to develop a selective cloud point extraction method for the separation and preconcentration of copper(II) prior to spectrophotometric determination. For this purpose dithizone was used as a complexing agent and the experimental solution was acidified with sulfuric acid. Triton X-114 was used as a surfactant and after phase separation, based on the cloud point of the mixture, the rich phase was diduted with tetrahydrofuran (THF) and the enriched analyte determined by spectrophotometric analysis. The chemical and thermodynamic variables affecting the complexation and phase separation were optimized. Calibration plot of absorbance vs. concentration was linear within the range of 15-250 ng ml -1 Cu( II ) the limit of detection being 4.6 ng ml -1. The proposed procedure was successfully applied to the determination of copper in liver samples.

Development of a cloud point extraction and preconcentration method for Cd and Ni prior to flame atomic absorption spectrometric determination

In this work a new cloud point extraction (CPE) methodology was developed for the separation and preconcentration of cadmium and nickel. The analyte in the initial aqueous solution was complexed with dithizone and Triton X-114 was added as surfactant. After phase separation, based on the cloud point of the mixture, and dilution of the surfactant-rich phase with tetrahydrofuran (THF), the enriched analytes were determined by flame atomic absorption spectrometry. After optimization of the complexation and extraction conditions and preconcentration of only 10 ml of sample in the presence of 0.05% Triton X-114, the enhancement factors of 52 and 39 and the detection limits of 0.31 μg l −1 and 1.2 μg l −1 were obtained for cadmium and nickel respectively. The proposed method was applied satisfactorily to the determination of cadmium and nickel in water samples.

Cloud-point extraction of nodularin-R from natural waters

A cloud-point extraction (CPE) technique for the determination of a cyanobacterial hepatotoxin, nodularin-R, in aqueous media using a cationic surfactant, tricaprylmethylammonium chloride (Aliquat-336), was developed. Cloud-point phase separation of Aliquat-336 at ambient temperature was induced by the addition of sodium sulfate. The Aliquat-336/Na 2SO 4 CPE system displayed large preconcentration factor, F C, for nodularin-R. At the operational CPE conditions, F C of 709.2 was achieved. Distribution constant, K D, of the distribution of nodularin-R between the surfactant-rich and aqueous phases of the CPE system was estimated to be (4.94±0.8)×10 3. Coupled to liquid chromatography with UV detection, the CPE method offered a detection limit of 330 pg ml −1 (in freshwater)/1.3 ng ml −1 (in seawater) and a repeatability of 6.4% (in freshwater) ( n=7, P<0.05) for nodularin-R in a sample of 25 ml. The CPE is a rapid process and no cleanup step is required. Effects of pH, natural abundant anion (chloride) and dissolved organic matters (DOM, humic acid, HA) on the extraction efficiency were evaluated. A double CPE technique was developed to overcome interferences encountered in the analysis of environmental samples. Applicability of the new method to the determination of nodularin-R in real coastal marine water samples has also been demonstrated.

Interaction between polyoxyethylene nonyl phenyl ether (n=9) and gold (III) ion in the adsorbed film and micelle

A thermodynamic method was employed to analyze the surface tension data for studying the adsorption at the interface and micelle formation of an aqueous solution of polyoxyethylene nonyl phenyl ether having an average of nine oxyethylene units (PONPE-9) and that of PONPE-9 and gold (III) ion mixtures at pH 3, 7, and 10. The results suggested the existence of attractive interaction between PONPE-9 and gold in the adsorbed film and micelle and that the interaction strength decreases in the order pH 3, pH 10, and pH 7. This result was in accord with the percent extraction of gold obtained from the cloud point extraction method where the efficiency relies on the strength of the interaction between analytes and the surfactant. Thus, this study confirmed the usefulness of the thermodynamic equations developed.

Cloud-point extraction and preconcentration of cyanobacterial toxins (microcystins) from natural waters using a cationic surfactant.

A new cloud-point extraction and preconcentration method using a cationic surfactant, Aliquat-336 (tricaprylylmethylammonium chloride), has been developed for the determination of cyanobacterial toxins, microcystins, in natural waters. Sodium sulfate was used to induce phase separation at 25 degrees C. The phase behavior of Aliquat-336 with respect to concentration of Na2SO4 was studied. The cloud-point system revealed a very high phase volume ratio compared to other established systems of nonionic, anionic, and cationic surfactants. At pH 6-7, it showed an outstanding selectivity in analyte extraction for anionic species. Only MC-LR and MC-YR, which are known to be predominantly anionic, were extracted (with averaged recoveries of 113.9 +/- 9% and 87.1 +/- 7%, respectively). MC-RR, which is likely to be amphoteric at the above pH range, was not detectable in the extract. Coupled to HPLC/UV separation and detection, the cloud-point extraction method (with 2.5 mM Aliquat-336 and 75 mM Na2SO4 at 25 degrees C) offered detection limits of 150 +/- 7 and 470 +/- 72 pg/mL for MC-LR and MC-YR, respectively, in 25 mL of deionized water. Repeatability of the method was 7.6% for MC-LR and 7.3% for MC-YR. The cloud-point extraction process can be completed within 10-15 min with no cleanup steps required. Applicability of the new method to the determination of microcystins in real samples was demonstrated using natural surface waters collected from a local river and a local duck pond spiked with realistic concentrations of microcystins. Effects of salinity and organic matter (TOC) content in the water sample on the extraction efficiency were also studied.