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.     

Evaluation of a cloud point extraction method for the preconcentration and quantification of silver nanoparticles in water samples by ETAAS

ABSTRACT

A simple and reliable analytical method using instrumentation available in most of the laboratories has been developed for the separation and determination of silver nanoparticles in water samples. Cloud point extraction (CPE) was used for the separation of silver nanoparticles (AgNPs) from the sample and these nanoparticles were then determined by electrothermal atomic absorption spectrometry (ETAAS). Parameters related to the cloud point extraction procedure (Triton X-114 concentration, type of complexing agent (EDTA or Na₂S₂O₃), pH, incubation temperature, incubation and centrifugation time) were selected using a multivariate approach (designs of experiments); 8.6% (v/v) Triton X-114, 750 µL saturated EDTA and pH 7 were selected as the optimum conditions. Calibration standards in a concentration range from 0 to 10 µg L^?1 of AgNPs were subjected to the CPE procedure to obtain quantitative recoveries. The LOD and LOQ were 0.04 and 0.13 µg L^?1, respectively. The method is selective for the extraction of AgNPs, and ionic Ag remains in the aqueous phase. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) was used to evaluate the effect of the CPE procedure in particle size, and no changes were observed. Finally, the procedure was applied to wastewater samples spiked with nanoparticles with quantitative recoveries.     

Sensitive ergotamine determination in pharmaceuticals and biological samples using cloud point preconcentration and spectrofluorimetric detection

A new cloud point extraction (CPE) method for ergotamine analysis using fluorimetric detection is described. Ergotamine from an aqueous solution was preconcentrated into a smaller surfactant-rich phase using nonionic surfactant polyoxyethylene(7.5)nonylphenylether (PONPE 7.5). Differently from the conventional CPE procedure in which the resulting surfactant-rich phase is diluted by a fluidificant before its analysis, in this method the fluorescence measurements were carried out directly onto the undiluted surfactant-rich phase. The high viscosity provided by the undiluted surfactant rich phase greatly improved the fluorescence emission of ergotamine, leading to a total enhancement factor of 1325. This spectral advantage plus the preconcentration factor achieved, contributed to the method sensitivity allowing the ergotamine determination at trace level concentration. Under optimal experimental conditions, a linear calibration curve was obtained from 3.81 × 10⁻⁷ to 1.10 μg mL⁻¹, with detection and quantification limits of 0.11 and 0.38 pg mL⁻¹, respectively. The accuracy and versatility of the present methodology were proved by analyzing ergotamine in real samples of different natures such as pharmaceuticals, urine and saliva.     

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%.     

Cloud point extraction for the determination of As(III) in water samples by electrothermal atomic absorption spectrometry

Cloud point extraction was applied as a preconcentration step for electrothermal atomic absorption spectrometry (ETAAS) determination of As(III) in aqueous solutions. After complexation with ammonium pyrrolidinedithiocarbamate, the analyte was quantitatively extracted to the surfactant-rich phase in the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) after centrifugation. 0.1 mol L⁻¹ HNO₃ in methanol was added to the surfactant-rich phase before ETAAS determination. The precision (R.S.D.) for 11 replicate determinations of 5.0 μg L⁻¹ of As(III) was 3.0%. The concentration factor, which is defined as the concentration ratio of the analyte in the final diluted surfactant-rich extract ready for ETAAS determination and in the initial solution, was 36 for As(III). The linear concentration range was from 0.1 to 20 μg L⁻¹. The developed method was applied to the determination of As(III) in lake water and river water.     

Cloud point extraction for determination of cadmium in soft drinks by thermospray flame furnace atomic absorption spectrometry

Cloud point extraction (CPE) is proposed as a preconcentration procedure for the determination of Cd in soft drinks by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). The cadmium reacted with pyridyl-azo-naphthol (PAN) to form hydrophobic chelates, which were extracted into the micelles of Triton X-114 in a solution buffered at pH 9. NaCl was used for the phase separation. The variables which affect the preconcentration were optimized using a 2³ factorial design and central composite design (CCD). A response surface maximum point was obtained, and the critical values were a concentration of 0.13 mmol L^? 1 PAN, 0.03% m/v Triton X-114 and 2.3% m/v NaCl. Under the optimized conditions, after the extraction and preconcentration steps, a sample volume of 100 μL was introduced into the hot Ni tube using water as the carrier at a flow rate of 0.4 mL min^? 1. The values obtained for the detection limit, relative standard deviation and preconcentration factor were 0.0178 μg L^? 1, 4.1% (n = 8) and 55.5, respectively. The accuracy of the proposed method was demonstrated by performing addition-recovery experiments. Recoveries varied from 88 to 104%.     

Ultratrace determination of cadmium by cold vapor atomic absorption spectrometry after preconcentration with a simplified cloud point extraction methodology

A simplified micelle-mediated extraction methodology for the preconcentration of ultratrace levels of cadmium as a prior step to its determination by cold vapor atomic absorption spectrometry (CV-AAS) has been developed. The methodology is based on the cloud point extraction (CPE) of cadmium at pH 8 by using the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) without adding any chelating agent. Cadmium cold vapor was generated from 2 ml of the extracted surfactant-rich phase by means of sodium tetrahydroborate (3%, w/v) as a reducing agent and hydrochloric acid (0.2 mol l⁻¹) as a carrier solution. Several important variables that affect the cloud point extraction and cold vapor cadmium generation efficiency were investigated and optimized. The preconcentration of only 50 ml of solution in the presence of 0.06% (v/v) PONPE 7.5 gives an enhancement factor of 62. The calibration graph using the preconcentration system was linear in the range of 4-100 ng l⁻¹ with a correlation coefficient of 0.9992. Detection limit (3 s) obtained in the optimal conditions was 0.56 ng l⁻¹. The relative standard deviation (R.S.D.) for six replicate determinations at 20 ng l⁻¹ Cd level was 3.2%. The proposed method was successfully applied to the ultratrace determination of cadmium in water samples.     

Cloud point extraction of mercury with PONPE 7.5 prior to its determination in biological samples by ETAAS

Cloud point extraction (CPE) has been used for the pre-concentration of mercury, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and later analysis by electrothermal atomic absorption spectrometry (ETAAS) using polyethyleneglycolmono-p-nonyphenylether (PONPE 7.5) as surfactant. The chemical variables affecting the separation step were optimized. Under the optimum conditions, i.e, pH 8.5, cloud point temperature 80 degrees C, 5-Br-PADAP=4x10(-5) mol L(-1), PONPE 7.5=0.2%, sample volume=1.0 mL, an enhancement factor of 22-fold was reached. The lower limit of detection (LOD) obtained under the optimal conditions was 0.01 microg L(-1). The precision for 10 replicate determinations at 2.0 microg L(-1) Hg was 4.0% relative standard deviation (R.S.D.). The calibration graph using the pre-concentration system for mercury was linear with a correlation coefficient of 0.9994 at levels near the detection limits up to at least 16 microg L(-1). The method was successfully applied to the determination of mercury in biological samples and in certified reference material (QC METAL LL3).     

Preconcentration and determination of ultra trace amounts of arsenic(III) and arsenic(V) in tap water and total arsenic in biological samples by cloud point extraction and electrothermal atomic absorption spectrometry

A new approach for developing a cloud point extraction-electrothermal atomic absorption spectrometry has been described and used for determination of arsenic. The method is based on phase separation phenomenon of non-ionic surfactants in aqueous solutions. After reaction of As(V) with molybdate towards a yellow heteropoly acid complex in sulfuric acid medium and increasing the temperature to 55 °C, analytes are quantitatively extracted to the non-ionic surfactant-rich phase (Triton X-114) after centrifugation.To decrease the viscosity of the extract and to allow its pipetting by the autosampler, 100 μl methanol was added to the surfactant-rich phase. An amount of 20 μl of this solution plus 10 μl of 0.1% m/v Pd(NO₃)₂ were injected into the graphite tube and the analyte determined by electrothermal atomic absorption spectrometry.Total inorganic arsenic(III, V) was extracted similarly after oxidation of As(III) to As(V) with KMnO₄. As(III) was calculated by difference. After optimization of the extraction condition and the instrumental parameters, a detection limit (3σ_B) of 0.01 μg l⁻¹ with enrichment factor of 52.5 was achieved for only 10 ml of sample. The analytical curve was linear in the concentration range of 0.02-0.35 μg l⁻¹. Relative standard deviations were lower than 5%. The method was successfully applied to the determination of As(III) and As(V) in tap water and total arsenic in biological samples (hair and nail).     

Determination of ultra trace amounts of bismuth in biological and water samples by electrothermal atomic absorption spectrometry (ET-AAS) after cloud point extraction

A new approach for a cloud point extraction electrothermal atomic absorption spectrometric method was used for determining bismuth. The aqueous analyte was acidified with sulfuric acid (pH 3.0-3.5). Triton X-114 was added as a surfactant and dithizone was used as a complexing agent.After phase separation at 50 °C based on the cloud point separation of the mixture, the surfactant-rich phase was diluted using tetrahydrofuran (THF). Twenty microliters of the enriched solution and 10 μl of 0.1% (w/v) Pd(NO₃)₂ as chemical modifier were dispersed into the graphite tube and the analyte determined by electrothermal atomic absorption spectrometry. After optimizing extraction conditions and instrumental parameters, a preconcentration factor of 196 was obtained for a sample of only 10 ml. The detection limit was 0.02 ng ml⁻¹ and the analytical curve was linear for the concentration range of 0.04-0.60 ng ml⁻¹. Relative standard deviations were <5%.The method was successfully applied for the extraction and determination of bismuth in tap water and biological samples (urine and hair).     

Cloud point extraction procedure for flame atomic absorption spectrometric determination of lead(II) in sediment and water samples

The conditions for cloud point extraction of lead(II) from aqueous solutions were investigated and optimized. The procedure is based on the separation of Pb(II) – brillant cresyl blue (BCB) complexes into the micellar media by adding the surfactant Triton X-114. After phase separation, the surfactant-rich phase was dissolved with 1 mol L⁻¹ HNO₃ in ethanol and diluted with 1 mol L⁻¹ HNO₃ solution before lead was determined by flame atomic absorption spectrometry. Optimization of the pH, ligand and surfactant quantities, incubation time, temperature, viscosity, sample volume, and interfering ions was performed. The effects of the matrix ions were also examined. The detection limits for three times the standard deviations of the blank for lead were 7.5 μg L⁻¹ for water samples and 0.33 μg g⁻¹ for sediment samples. The validity of cloud point extraction was checked by employing certified reference samples of Lake Sediment IAEA-SL-1 and Sewage Sludge BCR-CRM 144R. The procedure was applied to natural waters and sediment samples with satisfactory results (recoveries >95%, relative standard deviations <6.4%).     

Analytical performance of ETAAS method for Cd, Co, Cr and Pb determination in blood fractions samples

An electrothermal atomic absorption method (ETAAS) for direct determination of several toxic trace elements (Cd, Co, Cr, Pb) in human blood fractions was developed, because of increasing interest of toxic elements distribution in various blood constituents. Zeeman background correction and pyrolitically coated graphite tubes with L’vov platforms were used. Centrifugation was employed for the separation of blood fractions at different centrifugal conditions at 1200 × g and 3000 × g. The samples were acid-digested by HNO₃ in closed tubes under high temperature and pressure before injection into graphite furnace. Two common modifiers were used and were compared for their effectiveness to the determination of each analyte at the examined blood fractions. The effect of modifier, matrix, calibration technique and peak characteristic (peak area and peak height) on the total variation of the method was examined by analysis of variance. The sensitivity and recovery (Cd 98-110%, Cr 93-109%, Co 95-106% and Pb 91-107%) of the developed method are presented for the various fractions. The overall precision (R.S.D.) using peak area (Cd 6.3-13.1%, Cr 8.2-13.9%, Co 7.4-8.5% and Pb 7.0-11.8%) and peak height measurements (Cd 1.1-9.3%, Cr 6.5-13.5%, Co 6.5-17.3% and Pb 6.9-14.8%) are also presented for pellet and supernatant solution. Standard addition technique was more accurate in terms of analyte recovery.     

Cloud point extraction: an alternative to traditional liquid-liquid extraction for lanthanides(III) separation

Cloud point extraction (CPE) was used to extract and separate lanthanum(III) and gadolinium(III) nitrate from an aqueous solution. The methodology used is based on the formation of lanthanide(III)-8-hydroxyquinoline (8-HQ) complexes soluble in a micellar phase of non-ionic surfactant. The lanthanide(III) complexes are then extracted into the surfactant-rich phase at a temperature above the cloud point temperature (CPT). The structure of the non-ionic surfactant, and the chelating agent-metal molar ratio are identified as factors determining the extraction efficiency and selectivity. In an aqueous solution containing equimolar concentrations of La(III) and Gd(III), extraction efficiency for Gd(III) can reach 96% with a Gd(III)/La(III) selectivity higher than 30 using Triton X-114. Under those conditions, a Gd(III) decontamination factor of 50 is obtained.     

浊点萃取-紫外可见分光光度法测定痕量金

建立了以四甲基联苯胺(TMB)为络合剂,非离子表面活性剂Triton-114为萃取剂的浊点萃取-紫外可见分光光度法测定痕量金的方法。考察了溶液的pH、络合剂和表面活性剂浓度、平衡温度和时间等条件对浊点萃取的影响。在最优条件下,该方法对金的富集倍数为12倍,线性范围为0～0.5μg/mL,检出限(3σ)为8.6ng/mL,相对标准偏差RSD为2.3%～3.6%(n=6),回收率在97%～102%之间。方法已用于工业废水中痕量金的测定。     

Determination of lead in water samples by graphite furnace atomic absorption spectrometry after cloud point extraction

Cloud point extraction (CPE) has been used for the pre-concentration of lead, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and later analysis by graphite furnace atomic absorption spectrometry (GFAAS) using octylphenoxypolyethoxyethanol (TritonX-114) as surfactant. The chemical variables affecting the separation phase were optimized. Separation of the two phases was accomplished by centrifugation for 15 min at 4000 rpm. Under the optimum conditions i.e., pH 8.0, cloud point temperature 40 °C, [5-Br-PADAP] = 2.5 × 10⁻⁵ mol l⁻¹, [Triton X-114] = 0.05%, added methanol volume = 0.15 ml, pre-concentration of only 10 ml sample permitted an enhancement factor of 50-fold. The lower limit of detection (LOD) obtained under the optimal conditions was 0.08 μg l⁻¹. The precision for 10 replicate determinations at 5 μg l⁻¹ Pb was 2.8% relative standard deviation (R.S.D.). The calibration graph using the pre-concentration system for lead was linear with a correlation coefficient of 0.9984 at levels near the detection limits up to at least 30 μg l⁻¹. The method was successfully applied to the determination of lead in water samples.     

Determination of mercury in biological samples by cold vapor atomic absorption spectrometry following cloud point extraction with salt-induced phase separation

Method development for the pre-concentration of mercury in human hair, dogfish liver and dogfish muscle samples using cloud-point extraction and cold vapor atomic absorption spectrometry is demonstrated. Before the extraction, the samples were submitted to microwave-assisted digestion in a mixture of H₂O₂ and HNO₃. Cloud point extraction was carried out using 0.5% (m/v) ammonium O,O-diethyldithiophosphate (DDTP) as the chelating agent and 0.3% (m/v) Triton X-114 as the non-ionic surfactant. Phase separation was induced after the addition of Na₂SO₄ to a final concentration of 0.2 mol L⁻¹. Aliquots of the final extract were transferred to PTFE tubes and NaBH₄ and HCl were added. The mercury vapor was driven to a non-heated quartz tube for measuring the absorbance. The results obtained with salt-induced phase separation were in good agreement with the certified values at a 95% confidence level. An enrichment factor of 10 allowed a detection limit of 0.4 ng g⁻¹ to be obtained, which demonstrates the high sensitivity of the proposed procedure for the determination of mercury at trace levels.     

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.     

浊点萃取-火焰原子吸收光谱法测定淡水鱼中痕量铅

采用以双硫腙为络合剂、Triton X-100为表面活性剂的新型浊点萃取体系富集淡水鱼中的痕量铅,并用火焰原子吸收光谱法对其进行测定。探讨了溶液pH、表面活性剂浓度、络合剂用量、平衡温度、平衡时间等对浊点萃取及测定灵敏度的影响,优化了实验条件。在最佳条件下测得铅的检出限为0.090μg/L,校准曲线相关系数为0.9999。该方法已用于淡水鱼中痕量铅的测定。     

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.     

Cloud point extraction as a sample enrichment technique for capillary electrophoresis–An overview

Abstract

Cloud point extraction (CPE) is a simple, inexpensive and green sample enrichment technique for different analytes in different matrices. In this technique surfactant solution is used at concentration above critical micelle concentration to extract the analytes from various matrices. Capillary electrophoresis (CE) and family of related techniques have emerged as powerful analytical techniques for pharmaceutical, biomedical, food and environmental analysis. In this review we have described the applications of CPE coupling with CE.