Determination of cadmium in rice and water by tungsten coil electrothermal vaporization-atomic fluorescence spectrometry and tungsten coil electrothermal atomic absorption spectrometry after cloud point extraction

In this work, the microsampling nature of tungsten coil electrothermal vaporization Ar/H₂ flame atomic fluorescence spectrometry (W-coil ETV-AFS) as well as tungsten coil electrothermal atomic absorption spectrometry (W-coil ET-AAS) was used with cloud point extraction (CPE) for the ultrasensitive determination of cadmium in rice and water samples. When the temperature of the extraction system is higher than the cloud point temperature of the selected surfactant Triton X-114, the complex of cadmium with dithizone can be quantitatively extracted into the surfactant-rich phase and subsequently separated from the bulk aqueous phase by centrifugation. The main factors affecting the CPE, such as concentration of Triton X-114 and dithizone, pH, equilibration temperature and incubation time, were optimized for the best extract efficiency. Under the optimal conditions, the limits of detection for cadmium by W-coil ETV-AFS and W-coil ET-AAS were 0.01 and 0.03 μg L⁻¹, with sensitivity enhancement factors of 152 and 93, respectively. The proposed methods were applied to the determination of cadmium in certified reference rice and water samples with analytical results in good agreement with certified values.     

Determination of Prometryne in water and soil by HPLC-UV using cloud-point extraction

A CPE-HPLC (UV) method has been developed for the determination of Prometryne. In this method, non-ionic surfactant Triton X-114 was first used to extract and pre-concentrate Prometryne from water and soil samples. The separation and determination of Prometryne were then carried out in an HPLC-UV system with isocratic elution using a detector set at 254 nm wavelength. The parameters and variables that affected the extraction were also investigated and the optimal conditions were found to be 0.5% of Triton X-114 (w/v), 3% of NaCl (w/v) and heat-assisted at 50 °C for 30 min. Using these conditions, the recovery rates of Prometryne ranged from 92.84% to 99.23% in water and 85.48% to 93.67% in soil, respectively, with all the relative standard deviations less than 3.05%. Limit of detection (LOD) and limit of quantification (LOQ) were 3.5 μg L⁻¹ and 11.0 μg L⁻¹ in water and 4.0 μg kg⁻¹ and 13.0 μg kg⁻¹ in soil, respectively. Thus, we developed a method that has proven to be an efficient, green, rapid and inexpensive approach for extraction and determination of Prometryne from soil samples.     

Separation and preconcentration of ultra trace amounts of beryllium in water samples using mixed micelle-mediated extraction and determination by inductively coupled plasma-atomic emission spectrometry

In the present study a cloud point extraction process using mixed micelle of the cationic surfactant cetyl-pyridinium chloride (CPC) and non-ionic surfactant Triton X-114 for extraction of beryllium from aqueous solutions is developed. The extraction of analyte from aqueous samples was performed in the presence of 1,8-dihydroxyanthrone as chelating agent in buffer media of pH 9.5. After phase separation, the surfactant-rich phase was diluted with 0.4 mL of a 60:40 methanol-water mixture containing 0.03 mL HNO₃. Then, the enriched analyte in the surfactant-rich phase was determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The different variables affecting the complexation and extraction conditions were optimized. Under the optimum conditions (i.e. 1.6 × 10⁻⁴ mol L⁻¹ 1,8-dihydroxyanthrone, 1.2 × 10⁻⁴ mol L⁻¹ CPC, 0.15% (v/v) Triton X-114, 50 °C equilibrium temperature) the calibration graph was linear in the range of 0.006-80 ng mL⁻¹ with detection limit of 0.001 ng mL⁻¹ and the precision (R.S.D.%) for five replicate determinations at 18 ng mL⁻¹ of Be(II) was better than 2.9%. In this manner the preconcentration and enrichment factors were 16.7 and 24.8, respectively. Under the presence of foreign ions no significant interference was observed. Finally, the proposed method was successfully utilized for the determination of this cation in water samples.     

Determination of Ultratrace Amounts of Copper(Ⅱ) in Water Samples by Electrothermal Atomic Absorption Spectrometry After Cloud Point Extraction

A novel approach was developed for the determination of ultratrace amounts of copper in water samples by using electrothermal atomic absorption spectrometry (ETAAS) after cloud point extraction (CPE). 1-( 2-Pyridylazo)-2-naphthol was used as the chelating reagent and Triton X-114 as the micellar-forming surfactant. CPE was conducted in a pH 8.0 medium at 40 ℃ for 10 min. After the separation of the phases by centrifugation, the surfactant-rich phase was diluted with 1 mL of a methanol solution of 0. 1 mol/L HNO3. Then 20 μL of the diluted surfactant-rich phase was injected into the graphite furnace for atomization in the absence of any matrix modifier. Various experimental conditions that affect the extraction and atomization processes were optimized. A detection limit of 5 ng/L was obtained after preconcentration. The linear dynamic range of the copper mass concentration was found to be 0-2.0ng/mL, and the relative standard deviation was found to be less than 3.1% for a sample containing 1.0 ng/mL Cu(Ⅱ). This developed method was successfully applied to the determination of ultratrace amounts of Cu in drinking water, tap water, and seawater samples.     

Separation and preconcentration of trace amounts of aluminum ions in surface water samples using different analytical techniques

A separation/preconcentration of aluminum (III) (Al³⁺) has been developed to overcome the problem of high matrix species, which may interfere with the determination of trace quantity of Al³⁺ in natural water samples. The separation of Al³⁺ in water samples was carried out from interfering cations by complexing them with 2-methyle 8-hyroxyquinoline (quinaldine) on activated silica. Whereas the separated trace amounts of Al³⁺ was preconcentrated by cloud point extraction (CPE), as prior step to its determination by spectrofluorimetry (SPF) and flame atomic absorption spectrometry (FAAS). The Al³⁺ react with 8-hydroxyquinoline (oxine) and then entrapped in non-ionic surfactant Triton X-114. The main factors affecting CPE efficiency, such as pH of sample solution, concentration of oxine and Triton X-114, equilibration temperature and time period for shaking were investigated in detail. The validity of separation/preconcentration of Al³⁺ was checked by certified reference material of water (SRM-1643e). After optimization of the complexation and extraction conditions, a preconcentration factor of 20 was obtained for Al³⁺ in 10 mL of natural water samples. The relative standard deviation for 6 replicates containing 100 μg L⁻¹ of Al³⁺ was 5.41 and 4.53% for SPF and FAAS, respectively. The proposed method has been applied for determination of trace amount of Al³⁺ in natural water samples with satisfactory results.     

Determination of estrogens in water by HPLC-UV using cloud point extraction

A method based on cloud point extraction was developed to determine four kinds of estrogens: estriol (E3), estradiol (E2), estrone (E1), and progesterone (P) in water by high performance liquid chromatography separation and ultraviolet detection (HPLC-UV). The non-ionic surfactant Triton X-114 was chosen as extractant solvent. The parameters affecting extraction efficiency, such as concentrations of Triton X-114 and Na₂SO₄, equilibration temperature, equilibration time and centrifugation time were evaluated and optimized. Under the optimum conditions, preconcentration factors of 99 for E3, 73 for E2, 152 for E1 and 86 for P were obtained for 10 mL water sample. The detection of limitation was 0.23 ng mL⁻¹ for E3, 0.32 ng mL⁻¹ for E2, 0.25 ng mL⁻¹ for E1 and 5.0 ng mL⁻¹ for P. The proposed method was successfully applied to the determination of trace amount of estrogens in wastewater treatment plant (WWTP) effluent water and exposure water with 10 ng mL⁻¹ E2 for toxicological study in our lab. For the case of WWTP effluent water samples, no estrogen was found. The accuracy of the proposed method was tested by recovery measurements of spiked samples and good recoveries of 81.2-99.5% were obtained.     

Cloud point extraction and spectrophotometric determination of Cu(II) in saturated saline solutions using 4-ethyl-1-(pyridin-2-yl)thiosemicarbazide

4-Ethyl-1-(pyridin-2-yl)thiosemicarbazide (HEPTS) has been used as a new complexing agent in cloud point extraction (CPE) for preconcentration and determination of trace amounts of copper in saturated saline medium. The chemical variables affecting the separation and determination processes were optimized. Copper(II) is preconcentrated using 0.05% (w/v) Triton X-114 and 10⁻⁴ M HEPTS at pH 6. The surfactant rich phase containing the complex was dissolved in 2 mL MeOH and determined spectrophotometrically. The calibration curve is linear in the 0.1–25 ng/mL copper range. The proposed method was applied successfully in the determination of copper in water and saturated saline samples. The reaction between CuSO₄ and HEPTS yields a deep-blue solid complex which is characterized by analytical and spectroscopic analyses.     

Development of a cloud point extraction and preconcentration method for determination of trace aluminum in mineral waters by FAAS

A cloud point extraction (CPE) method has been developed for the preconcentration of trace aluminum prior to its determination by flame atomic absorption spectrometry (FAAS). The CPE method is based on the complex of Al(III) with Xylidyl Blue (XB) and then entrapped in non-ionic surfactant Triton X-114. The main factors affecting CPE efficiency, such as pH of sample solution, concentration of XB and Triton X-114, equilibration temperature and time, were investigated in detail. An enrichment factor of 50 was obtained for the preconcentration of Al(III) with 50 mL solution. Under the optimal conditions, the detection limit of this method for Al(III) is 1.43 μg L^− 1, and the relative standard deviation is 2.7% at determination of 100 μg L^− 1 Al(III). The proposed method has been applied for determination of trace amount of aluminum in mineral water samples with satisfactory results. Also, the proposed method was applied to the certified reference materials. The results obtained were in good agreement with certified values.     

Micellar extraction and high performance liquid chromatography-ultra violet determination of some explosives in water samples

An analytical method based on the cloud point extraction combined with high performance liquid chromatography is used for the extraction, separation and determination of four explosives; octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN). These compounds are extracted by using of Triton X-114 and cetyl-trimethyl ammonium bromide (CTAB). After extraction, the samples were analyzed using a HPLC-UV system. The parameters affecting extraction efficiency (such as Triton X-114 and CTAB concentrations, amount of Na₂SO₄, temperature, incubation and centrifuge times) were evaluated and optimized. Under the optimum conditions, the preconcentration factor was 40 and the improvement factors of 34, 29, 61 and 42 with detection limits of 0.09, 0.14, 0.08 and 0.40 (μg L⁻¹) were obtained for HMX, RDX, TNT and PETN, respectively. The proposed method was successfully applied to the determination of these compounds in water samples and showed recovery percentages of 97-102% with RSD values of 2.13-4.92%.     

Development of a new sequential injection in-line cloud point extraction system for flame atomic absorption spectrometric determination of manganese in food samples

A preconcentration method for manganese determination by sequential injection cloud point extraction with subsequent detection by flame atomic absorption spectrometry (FAAS) has been developed. The enrichment of Mn was performed after a preliminary on-line cloud point extraction and entrapment of manganese-containing surfactant aggregated within a minicolumn packed with cotton. The laboratory-made reagent 4-(5′-bromo-2′-thiazolylazo)orcinol (Br-TAO) and the surfactant Triton X-114 were used for cloud point extraction. The manganese ions were eluted with sulphuric acid solution and directly introduced into the FAAS. Chemical and flow variables affecting the preconcentration were studied. Using a sample volume of 2.80 mL the limit of detection and enrichment factor were calculated to be 0.5 μg L⁻¹ and 14, respectively. The sample frequency is 48 h⁻¹, considering a total run cycle of 75 s. The accuracy of the proposed method has been demonstrated by the analysis of the certified reference biological materials rice flour and tomato leaves. The method has been applied to determination of manganese in food samples.     

Cloud point extraction for the determination of lead and cadmium in urine by graphite furnace atomic absorption spectrometry with multivariate optimization using Box–Behnken design

Cloud point extraction (CPE) is proposed as a pre-concentration procedure for the determination of Pb and Cd in undigested urine by graphite furnace atomic absorption spectrometry (GF AAS). Aliquots of 0.5 mL urine were acidified with HCl and the chelating agent ammonium O,O-diethyl dithiophosphate (DDTP) was added along with the non-ionic surfactant Triton X-114 at the optimized concentrations. Phase separation was achieved by heating the mixture to 50 °C for 15 min. The surfactant-rich phase was analyzed by GF AAS, employing the optimized pyrolysis temperatures of 900 °C for Pb and 800 °C for Cd, using a graphite tube with a platform treated with 500 μg Ru as permanent modifier. The reagent concentrations for CPE (HCl, DDTP and Triton X-114) were optimized using a Box–Behnken design. The response surfaces and the optimum values were very similar for aqueous solutions and for the urine samples, demonstrating that aqueous standards submitted to CPE could be used for calibration. Detection limits of 40 and 2 ng L^− 1 for Pb and Cd, respectively, were obtained along with an enhancement factor of 16 for both analytes. Three control urine samples were analyzed using this approach, and good agreement was obtained at a 95% statistical confidence level between the certified and determined values. Five real samples have also been analyzed before and after spiking with Pb and Cd, resulting in recoveries ranging from 97 to 118%.     

Determination of cadmium and zinc in water samples by flame atomic absorption spectrometry after cloud-point extraction

The phase-separation phenomenon of nonionic surfactants occurring in an aqueous solution was used for the extraction of Cd and Zn from water samples. After complexation with 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NDDBH) in hydrochloric acid medium (pH 1), the analytes were quantitatively extracted after centrifugation into the phase rich in the nonionic surfactant octylphenoxypolyethoxyethanol (Triton X-114). Tetrahydrofuran acidified with 0.1 M HCl was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry. The adopted concentrations for NDDBH, Triton X-114 and hydrochloric acid were all optimized. Detection limits (3σ) of 0.33 and 0.85 ng/mL along with enrichment factors of 157 and 118 for Cd and Zn, respectively, were achieved. The proposed method was applied to the determination of Cd and Zn in acidic solutions of certified reference materials. A comparison with certified values was performed for an evaluation of the accuracy, resulting in a good agreement according to the t-test at a 95% confidence level. The high efficiency of the cloud-point extraction to carry out the determination of the studied analytes in complex matrices was, therefore, demonstrated. The text was submitted by the authors in English.     

浊点萃取-火焰原子吸收光谱法测定食品和饮料中的痕量铜

研究了基于非离子表面活性剂TritonX-114和螯合剂二乙基氨基二硫代甲酸钠(DDTC)的浊点萃取-火焰原子吸收光谱法测定痕量铜的分析方法.考察了影响浊点萃取效率的参数,包括pH值、DDTC浓度、TritonX-114用量、平衡温度及时间等.在优化条件下,本法的检出限(3σ)为1.55μg/L,相对标准偏差RSD为3.4%(n=7,c=100μg/L),线性范围为0～250μg/L.将该法应用于茶叶标准样品(GBW07605)、奶粉和矿泉水等样品中痕量铜的测定,其回收率在96.7%～113.5%之间.     

Evaluation of a cloud point extraction approach for the preconcentration and quantification of trace CuO nanoparticles in environmental waters

The cloud point extraction (CPE) of commercial copper(II) oxide nanoparticles (CuO NPs, mean diameter of 28 nm) in water samples was fully investigated. Factors such as Triton X-114 (TX-114) concentration, pH, incubation temperature and time, were optimized. The effects of CuO NP behavior like agglomeration, dissolution, and surface adsorption of natural organic matter, Cu²⁺, and coating chemicals, on its recovery were studied. The results indicated that all the CPE factors had significant effects on the extraction efficiency. An enrichment factor of ∼89 was obtained under optimum CPE conditions. The hydrodynamic diameter of CuO NPs increased to 4–5 μm upon agglomeration of NP-micelle assemblies, and decreased at pH >10.0 at which the extraction efficiency was also lowered. The solubility and therefore, the loss of NPs were greatly enhanced at pH <8.5 and in the first 60 min of incubation, whereas it declined at elevated incubation temperatures. Our results showed that the dissolved organic carbon (DOC) >5 mg C L⁻¹ and Cu²⁺ >2 times that of CuO NPs, lowered and enhanced the extraction efficiency, respectively. Pre-treatment of samples with 3% w v⁻¹ of hydrogen peroxide and 10 mM of ethylenediaminetetraacetic acid minimized the interferences posed by DOC and Cu²⁺, respectively. The decrease in CPE efficiency was also evident for ligands like poly(ethylene glycol). The TX-114-rich phase could be determined with either inductively coupled plasma mass spectrometry following microwave digestion, or graphite furnace atomic absorption spectrometry. The detection limits for CuO NPs were 0.02 and 0.06 μg L⁻¹ using these techniques, respectively. The optimum sample pre-treatment and CPE conditions were successfully applied to the river and wastewater samples. The relative recoveries of CuO NPs spiked at 5–100 μg L⁻¹ (as Cu) in these samples were in the range of between 59.2 and 108.2%. The approach demonstrates a robust analytical method for detecting trace levels of CuO NPs at their original states and assessing their exposure risks in real aquatic environments.     

Cloud point extraction–thermospray flame quartz furnace atomic absorption spectrometry for determination of ultratrace cadmium in water and urine

A simple, low cost and highly sensitive method based on cloud point extraction (CPE) for separation/preconcentration and thermospray flame quartz furnace atomic absorption spectrometry was proposed for the determination of ultratrace cadmium in water and urine samples. The analytical procedure involved the formation of analyte-entrapped surfactant micelles by mixing the analyte solution with an ammonium pyrrolidinedithiocarbamate (APDC) solution and a Triton X-114 solution. When the temperature of the system was higher than the cloud point of Triton X-114, the complex of cadmium-PDC entered the surfactant-rich phase and thus separation of the analyte from the matrix was achieved. Under optimal chemical and instrumental conditions, the limit of detection was 0.04 μg/L for cadmium with a sample volume of 10 mL. The analytical results of cadmium in water and urine samples agreed well with those by ICP-MS.     

β-Cyclodextrin-cross-linked polymer as solid phase extraction material coupled with inductively coupled plasma mass spectrometry for the analysis of trace Co(II)

A sensitive method for the separation/analysis of Co(II) was described. The β-cyclodextrin cross-linked polymer (β-CDCP) was synthesized and used as solid phase extraction material (SPE) to separate/pre-concentrate trace cobalt coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of Co(II). The method was based on α-pyridylazo-β-naphthol (PAN) as the complexing agent for Co(II)-PAN at neutral condition and the adsorption behavior of Co(II)-PAN on β-CDCP was studied. Further, p-octylpolyethylene-glycolphenyl ether (Triton X-100) as environment-friendly eluant was used. The linear range, detection limit (DL) and the relative standard deviation (R.S.D.) was 5.0-160.0 ng/mL, 5.84 ng/L and 2.27% (n = 3, c = 30.0 ng/mL) respectively. The enhancement factor was 10. Moreover, the β-CDCP could be used repeatedly and offered better recovery and estimation of standard samples.     

Flame atomic absorption spectrometric determination of trace amounts of palladium,gold and nickel after cloud point extraction

In this article, a sensitive cloud point extraction procedure for the preconcentration of trace amounts of palladium, gold and nickel prior to their determination by flame atomic absorption spectrometry has been developed. The cloud point extraction method is based on the complexation of Pd(II), Au(II), and Ni(II) ions with 1-(2-pyridylazo)-2-naphthol and entrapping in non-ionic surfactant Triton X-114. The main factors affecting cloud point extraction efficiency, such as pH of sample solution, concentration of 1-(2-pyridylazo)-2-naphthol and Triton X-114, equilibration temperature and time, were investigated in detail. Under the optimized conditions, calibration curves were constructed for the determination of palladium, gold and nickel according to the general procedure. Linearity was maintained from 0.01 to 1.0 μg/mL for palladium, 10.0 μg/mL to 1.5 μg/mL for gold, and 10.0 μg/mL to 0.5 μg/mL for nickel. Detection limits based on three times the standard deviation of the blank divided by the slope of analytical curve (3Sb/m) for Pd(II), Au(III), and Ni(11) ions were 3.4, 3.9, and 2.4 μg/mL, respectively. Seven replicate determination of a mixture of 0.5 μg/mL palladium and gold and 0.2 μg/mL nickel gave a mean absorbance of 0.174, 0.150, and 0.201 with relative standard deviation ±1.5, ±1.3, and ±1.8%, respectively. The high efficiency of cloud point extraction to carry out the determination of analytes in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of palladium, gold and nickel in certified reference material and water samples with satisfactory results.     

Taguchi OA16 orthogonal array design for the optimization of cloud point extraction for selenium determination in environmental and biological samples by tungsten-modified tube electrothermal atomic absorption spectrometry

Orthogonal array design (OAD) was applied for the first time to optimize cloud point extraction (CPE) conditions for Se(IV) determination by electrothermal atomic absorption spectrometry (ETAAS) in environmental and biological samples. Selenium was reacted with o-phenylenediamine to form piazselenol in an acidic medium (pH 2). Using Triton X-114, as surfactant, piazselenol was quantitatively extracted into small volume (about 30 μL) of the surfactant-rich phase after centrifugation. Five relevant factors, i.e. surfactant concentration, pH, ionic strength, equilibrium time and temperature were selected and the effects of each factor were studied at four levels on the extraction efficiency of Se(IV) and optimized. The statistical analysis revealed that the most important factors contributing to the extraction efficiency are ionic strength, pH and percent of surfactant. Based on the results obtained from the analysis of variance (ANOVA), the optimum conditions for extraction were established as: pH 6; vial temperature = 50 °C; extraction time = 7 min and 0.3% (w/v) of Triton X-114. The method was permitted to obtain a detection limit of 0.09 ng mL⁻¹ and two linear calibration ranges from 0.6 to 1.0 and 1.0 to 80.0 ng mL⁻¹ Se. The precision (%RSD) of the extraction and determination for the six replicates of Se at 20 ng mL⁻¹ was better than 3.6% and the enrichment factor of 63.5 was achieved. The studied analyte was successfully extracted and determined with high efficiency using cloud point extraction method in water and biological matrices.     

Highly selective cloud point extraction and preconcentration of trace amounts of silver in water samples using synthesized Schiff’s base followed by flame atomic absorption spectrometric determination

A simple and useful method employing cloud point extraction is proposed for the preconcentration and separation of silver in water samples. The silver cation reacts with bis(2-mercaptoanil) acetylacetone (BMAA) at pH 6. The resulting compound is subsequently entrapped in the Triton X-114 micelles. After optimization of the complexation and extraction conditions, a preconcentration factor of 50 was obtained (volume of initial sample was 10 mL). As an analytical example, trace amounts of Ag were determined, after preconcentration, in a complex aqueous matrix such as seawater using flame atomic absorption spectrometry. The calibration curve was linear in the range 2–200 ng/mL and the limit of detection was 0.43 ng/mL. The relative standard deviation was lower than 2.4%. The text was submitted by the authors in English.     

Determination of ultra-trace amount methyl-, phenyl- and inorganic mercury in environmental and biological samples by liquid chromatography with inductively coupled plasma mass spectrometry after cloud point extraction preconcentration

The cloud point extraction (CPE) preconcentration of ultra-trace amount of mercury species prior to reverse-phase high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS) detection was studied. Mercury species including methyl-, ethyl-, phenyl- and inorganic mercury were transformed into hydrophobic chelates by reaction with sodium diethyldithiocarbamate, and the hydrophobic chelates were extracted into a surfactant-rich phase of Triton X-114 upon heating in a water bath at 40 °C. Ethylmercury was found partially decomposed during the CPE process, and was not included in the developed method. Various experimental conditions affecting the CPE preconcentration, HPLC separation, and ICP-MS determination were optimized. Under the optimized conditions, detection limits of 13, 8 and 6 ng l⁻¹ (as Hg) were achieved for MeHg⁺, PhHg⁺ and Hg²⁺, respectively. Seven determinations of a standard solution containing the three mercury species each at 0.5 ng ml⁻¹ level produced relative standard deviations of 5.3, 2.3 and 4.4% for MeHg⁺, PhHg⁺ and Hg²⁺, respectively. The developed method was successfully applied for the determination of the three mercury species in environmental water samples and biological samples of human hair and ocean fish.