Dispersive liquid-liquid microextraction combined with graphite furnace atomic absorption spectrometry: ultra trace determination of cadmium in water samples

Dispersive liquid-liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 μL methanol (disperser solvent) containing 34 μL carbon tetrachloride (extraction solvent) and 0.00010 g ammonium pyrrolidine dithiocarbamate (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with ammonium pyrrolidine dithiocarbamate, and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25 ± 1 μL). Then a 20 μL of sedimented phase containing enriched analyte was determined by GF AAS.Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 125 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the rage of 2-20 ng L⁻¹ with detection limit of 0.6 ng L⁻¹. The relative standard deviation (R.S.D.s) for ten replicate measurements of 20 ng L⁻¹ of cadmium was 3.5%. The relative recoveries of cadmium in tap, sea and rivers water samples at spiking level of 5 and 10 ng L⁻¹ are 108, 95, 87 and 98%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on-line liquid-liquid extraction, single drop microextraction (SDME), on-line solid phase extraction (SPE) and co-precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL).     

On-line sequential injection dispersive liquid-liquid microextraction system for flame atomic absorption spectrometric determination of copper and lead in water samples

A simple, sensitive and powerful on-line sequential injection (SI) dispersive liquid-liquid microextraction (DLLME) system was developed as an alternative approach for on-line metal preconcentration and separation, using extraction solvent at microlitre volume. The potentials of this novel schema, coupled to flame atomic absorption spectrometry (FAAS), were demonstrated for trace copper and lead determination in water samples. The stream of methanol (disperser solvent) containing 2.0% (v/v) xylene (extraction solvent) and 0.3% (m/v) ammonium diethyldithiophosphate (chelating agent) was merged on-line with the stream of sample (aqueous phase), resulting a cloudy mixture, which was consisted of fine droplets of the extraction solvent dispersed entirely into the aqueous phase. By this continuous process, metal chelating complexes were formed and extracted into the fine droplets of the extraction solvent. The hydrophobic droplets of organic phase were retained into a microcolumn packed with PTFE-turnings. A portion of 300 μL isobutylmethylketone was used for quantitative elution of the analytes, which transported directly to the nebulizer of FAAS. All the critical parameters of the system such as type of extraction solvent, flow-rate of disperser and sample, extraction time as well as the chemical parameters were studied. Under the optimum conditions the enhancement factor for copper and lead was 560 and 265, respectively. For copper, the detection limit and the precision (R.S.D.) were 0.04 μg L⁻¹ and 2.1% at 2.0 μg L⁻¹ Cu(II), respectively, while for lead were 0.54 μg L⁻¹ and 1.9% at 30.0 μg L⁻¹ Pb(II), respectively. The developed method was evaluated by analyzing certified reference material and applied successfully to the analysis of environmental water samples.     

Monitoring of selenium in water samples using dispersive liquid-liquid microextraction followed by iridium-modified tube graphite furnace atomic absorption spectrometry

A simple and powerful microextraction technique was used for determination of selenium in water samples using dispersive liquid-liquid microextraction (DLLME) followed by graphite furnace atomic absorption spectrometry (GF AAS). DLLME and simultaneous complex formation was performed with rapid injection of a mixture containing ethanol (disperser solvent), carbon tetrachloride (extraction solvent) and ammonium pyrrolidine dithiocarbamate (APDC, chelating agent) into water sample spiked with selenium. After centrifuging, fine droplets of carbon tetrachloride, which were dispersed among the solution and extracted Se-APDC complex, sediment at the bottom of the conical test tube. The concentration of enriched analyte in the sedimented phase was determined by iridium-modified pyrolitic tube graphite furnace atomic absorption spectrometry. The concentration of selenate was obtained as the difference between the concentration of selenite after and before pre-reduction of selenate to selenite. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of chelating agent were optimized. Under the optimum conditions, the enrichment factor of 70 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the range of 0.1-3 μg L^− 1 with detection limit of 0.05 μg L^− 1. The relative standard deviation (RSDs) for ten replicate measurements of 2.00 μg L^− 1 of selenium was 4.5%. The relative recoveries of selenium in tap, river and sea water samples at spiking level of 2.00 μg L^− 1 were 106, 96 and 98%, respectively.     

Dispersive liquid-liquid microextraction preconcentration of palladium in water samples and determination by graphite furnace atomic absorption spectrometry

A new method for the determination of palladium was developed by dispersive liquid-liquid microextraction preconcentration and graphite furnace atomic absorption spectrometry detection. In the proposed approach, diethyldithiocarbamate (DDTC) was used as a chelating agent, and carbon tetrachloride and ethanol were selected as extraction and dispersive solvent. Some factors influencing the extraction efficiency of palladium and its subsequent determination, including extraction and dispersive solvent type and volume, pH of sample solution, concentration of the chelating agent and extraction time, were studied and optimized. Under the optimum conditions, the enrichment factor of this method for palladium reached at 156. The detection limit for palladium was 2.4 ng L⁻¹ (3σ), and the relative standard deviation (R.S.D.) was 4.3% (n = 7, c = 1.0 ng mL⁻¹). The method was successfully applied to the determination of trace amount of palladium in water samples.     

Ligandless dispersive liquid-liquid microextraction for the separation of trace amounts of silver ions in water samples and flame atomic absorption spectrometry determination

In this article, a new ligandless dispersive liquid-liquid microextraction method has been developed for preconcentration of trace quantities of silver as a prior step to its determination by flame atomic absorption spectrometry. In the proposed approach, carbon tetrachloride and ethanol were used as extraction and dispersive solvents. Several factors that may be affected on the extraction process, like, extraction solvent, disperser solvent, the volume of extraction and disperser solvent, pH of the aqueous solution and extraction time were optimized. Under the optimal conditions, the calibration curve was linear in the range of 5.0 ng mL⁻¹ to 2.0 μg mL⁻¹ of silver with R² = 0.9995 (n = 9) and detection limit based on three times the standard deviation of the blank (3S_b) was 1.2 ng mL⁻¹ in original solution. The relative standard deviation for eight replicate determination of 0.5 μg mL⁻¹ silver was ±1.5%. The high efficiency of dispersive liquid-liquid microextraction to carry out the determination of silver in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of silver in standard and water samples with satisfactory results.     

Temperature-controlled ionic liquid-liquid-phase microextraction for the pre-concentration of lead from environmental samples prior to flame atomic absorption spectrometry

Hydrophobic ionic liquid could be dispersed into infinite droplets under driving of high temperature, and then they can aggregate as big droplets at low temperature. Based on this phenomenon a new liquid-phase microextraction for the pre-concentration of lead was developed. In this experiment, lead was transferred into its complex using dithizone as chelating agent, and then entered into the infinite ionic liquid drops at high temperature. After cooled with ice-water bath and centrifuged, lead complex was enriched in the ionic liquid droplets. Important parameters affected the extraction efficiency had been investigated including the pH of working solution, amount of chelating agent, volume of ionic liquid, extraction time, centrifugation time, and temperature, etc. The results showed that the usually coexisting ions containing in water samples had no obvious negative effect on the recovery of lead. The experimental results indicated that the proposed method had a good linearity (R = 0.9951) from 10 ng mL⁻¹ to 200 ng mL⁻¹. The precision was 4.4% (RSD, n = 6) and the detection limit was 9.5 ng mL⁻¹. This novel method was validated by determination of lead in four real environmental samples for the applicability and the results showed that the proposed method was excellent for the future use and the recoveries were in the range of 94.8-104.1%.     

A novel method for the determination of trace copper in cereals by dispersive liquid-liquid microextraction based on solidification of floating organic drop coupled with flame atomic absorption spectrometry

A novel,simple,rapid,efficient and environment-friendly method for the determination of trace copper in cereal samples was developed by using dispersive liquid-liquid microextraction based on solidification of floating organic drop(DLLME-SFO) followed by flame atomic absorption spectrometry.In the DLLME-SFO,copper was complexed with 8-hydroxy quinoline and extracted into a small volume of 1-dodecanol,which is of low density,low toxicity and proper melting point near room temperature. The experimental parameters affecting the extraction efficiency were investigated and optimized.Under the optimum conditions, the calibration graph exhibited linearity over the range of 0.5—500 ng/mL with the correlation coefficient(r) of 0.9996.The enrichment factor was 122 and the limit of detection was 0.1 ng/mL.The method was applied to the determination of copper in the complex matrix samples such as rice and millet with the recoveries for the spiked samples at 5.0 and 10.0 u,g/g falling in the range of 92.0-98.0%and the relative standard deviation of 3.9-5.7%.     

A sensitive and selective method for determination of gold(III) based on electrothermal atomic absorption spectrometry in combination with dispersive liquid-liquid microextraction using dicyclohexylamine

A combined method with dispersive liquid-liquid microextraction (DLLME) and electrothermal atomic absorption spectrometry (ETAAS) has been developed for determining gold(III). Dicyclohexylamine, a new extractant for gold(III), showed excellent performance in DLLME. Acetone was indispensable to the quantitative extraction of gold(III), contributing to decrease in hydration, decrease in the difference in the dielectric constants between the supernatant phase and the sedimented phase, and dissolution of a part of chloroform as an extraction solvent to the supernatant phase as well as improvement of dipersibility. In DLLME using a mixture of 1.0 mL of acetone and 100 μL of chloroform containing 50 mmol L⁻¹ of dicyclohexylamine, gold(III) could be extracted selectively and effectively from 8 mL of a sample solution in the presence of iron(III), cobalt(II), nickel(II), copper(II), palladium(II), and platinum(IV) at pH 1. The extracted gold(III) was determinable by ETAAS; the detection limit was 0.002 μg L⁻¹ (three times the standard deviation of the blank values, n = 8) as a gold(III) concentration in 8 mL of sample solution. The proposed method was applicable to the determination of gold in platinum metal and its alloy as well as effluent without any interference by the matrices.     

Graphene-based solid-phase extraction combined with flame atomic absorption spectrometry for a sensitive determination of trace amounts of lead in environmental water and vegetable samples

Graphene, a novel class of carbon nanostructures, has great promise for use as sorbent materials because of its ultrahigh specific surface area. A new method using a column packed with graphene as sorbent was developed for the preconcentration of trace amounts of lead (Pb) using dithizone as chelating reagent prior to its determination by flame atomic absorption spectrometry. Some effective parameters on the extraction and complex formation were selected and optimized. Under optimum conditions, the calibration graph was linear in the concentration range of 10.0–600.0 μg L⁻¹ with a detection limit of 0.61 μg L⁻¹. The relative standard deviation for ten replicate measurements of 20.0 and 400.0 μg L⁻¹ of Pb were 3.56 and 3.25%, respectively. Comparative studies showed that graphene is superior to other adsorbents including C18 silica, graphitic carbon, and single- and multi-walled carbon nanotubes for the extraction of Pb. The proposed method was successfully applied in the analysis of environmental water and vegetable samples. Good spiked recoveries over the range of 95.3–100.4% were obtained. This work not only proposes a useful method for sample preconcentration, but also reveals the great potential of graphene as an excellent sorbent material in analytical processes.     

Development of a sequential injection dispersive liquid-liquid microextraction system for electrothermal atomic absorption spectrometry by using a hydrophobic sorbent material: Determination of lead and cadmium in natural waters

A novel on-line sequential injection (SI) dispersive liquid-liquid microextraction (DLLME) system coupled to electrothermal atomic absorption spectrometry (ETAAS) was developed for metal preconcentration in micro-scale, eliminating the laborious and time consuming procedure of phase separation with centrifugation. The potentials of the system were demonstrated for trace lead and cadmium determination in water samples. An appropriate disperser solution which contains the extraction solvent (xylene) and the chelating agent (ammonium pyrrolidine dithiocarbamate) in methanol is mixed on-line with the sample solution (aqueous phase), resulting thus, a cloudy solution, which is consisted of fine droplets of xylene, dispersed throughout the aqueous phase. Three procedures are taking place simultaneously: cloudy solution creation, analyte complex formation and extraction from aqueous phase into the fine droplets of xylene. Subsequently the droplets were retained on the hydrophobic surface of PTFE-turnings into the column. A part of 30 μL of the eluent (methyl isobutyl ketone) was injected into furnace graphite for analyte atomization and quantification. The sampling frequency was 10 h⁻¹, and the obtained enrichment factor was 80 for lead and 34 for cadmium. The detection limit was 10 ng L⁻¹ and 2 ng L⁻¹, while the precision expressed as relative standard deviation (RSD) was 3.8% (at 0.5 μg L⁻¹) and 4.1% (at 0.03 μg L⁻¹) for lead and cadmium respectively. The proposed method was evaluated by analyzing certified reference materials and was applied to the analysis of natural waters.     

Sequential injection dispersive liquid-liquid microextraction based on fatty alcohols and poly(etheretherketone)-turnings for metal determination by flame atomic absorption spectrometry

A novel, simple and efficient sequential injection (SI) on-line dispersive liquid-liquid microextraction (DLLME) procedure was described and was demonstrated for the assay of trace silver determination by flame atomic absorption spectrometry (FAAS). Fatty alcohols, such as 1-undecanol and 1-dodecanol, were examined as extraction solvents at microlitre volume, overcoming a major problem of the DLLME methods, the high toxicity of the extraction solvents used. Furthermore, the extractant fine droplets can be easily separated from the aqueous phase using a micro-column packed with a novel hydrophobic sorbent material, poly(etheretherketone)-turnings. In this method fine droplets of 1-dodecanol were on-line generated and dispersed into the stream of aqueous sample. By this continuous process, silver diethyldithiocarbamate (Ag-DDTC) complex was formed and extracted into the dispersed extraction solvent. No specific conditions such as ice bath for low temperature or special tools are required for extractant isolation. All significant parameters that influence the efficiency of the system such as sample acidity, concentration of complexing reagent and extraction solvent, flow-rate of disperser and sample solution as well as the preconcentration time were investigated and optimized by full factorial design. Under the optimized conditions a detection limit of 0.15 μg L⁻¹, a relative standard deviation (RSD) of 2.9% at 5.00 μg L⁻¹ Ag(I) concentration level and an enhancement factor of 186 were obtained. The developed method was evaluated by analyzing certified reference material and was applied successfully to the analysis of environmental water samples.     

Determination of organochlorine pesticides in water samples by dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry

A rapid and simple dispersive liquid-liquid microextraction (DLLME) has been developed to preconcentrate eighteen organochlorine pesticides (OCPs) from water samples prior to analysis by gas chromatography-mass spectrometry (GC-MS). The studied variables were extraction solvent type and volume, disperser solvent type and volume, aqueous sample volume and temperature. The optimum experimental conditions of the proposed DLLME method were: a mixture of 10 μL tetrachloroethylene (extraction solvent) and 1 mL acetone (disperser solvent) exposed for 30 s to 10 mL of the aqueous sample at room temperature (20 °C). Centrifugation of cloudy solution was carried out at 2300 rpm for 3 min to allow phases separation. Finally, 2 μL of extractant was recovered and injected into the GC-MS instrument. Under the optimum conditions, the enrichment factors ranged between 46 and 316. The calculated calibration curves gave a high-level linearity for all target analytes with correlation coefficients ranging between 0.9967 and 0.9999. The repeatability of the proposed method, expressed as relative standard deviation, varied between 5% and 15% (n = 8), and the detection limits were in the range of 1-25 ng L⁻¹. The LOD values obtained are able to detect these OCPs in aqueous matrices as required by EPA methods 525.2 and 625. Analysis of spiked real water samples revealed that the matrix had no effect on extraction for river, surface and tap waters; however, urban wastewater sample shown a little effect for five out of eighteen analytes.     

有机悬浮固化分散液-液微萃取测定水样中痕量铅

建立了以二乙基二硫代氨基甲酸钠为配位剂,十二醇为萃取剂,乙醇为分散剂的悬浮固化分散液-液微萃取—火焰原子吸收光谱法测定水样中痕量铅的方法。详细探讨了影响萃取效率的因素。优化条件为:二乙基二硫代氨基甲酸钠的用量为10-6 mol,十二醇体积为90.00μL,乙醇体积为1.00 mL,pH为7.00。在最佳条件下,铅的检出限为1.12μg/L,富集倍率为16.00,线性范围5.00～600.00μg/L,对含有20.00μg/L和600.00μg/L Pb的标准溶液平行萃取测定11次,测定结果的RSD分别为3.73%和2.62%。本方法应用于自来水、河水及海水中痕量铅的分析,加标回收率为90.10%～100.70%。     

Multiwalled carbon nanotubes microcolumn preconcentration and determination of gold in geological and water samples by flame atomic absorption spectrometry

The potential of multiwalled carbon nanotubes (MWNTs) as solid-phase extraction adsorbent for the separation and preconcentration of gold has been investigated. Gold could be adsorbed quantitatively on MWNTs in the pH range of 1–6, and then eluted completely with 2 mL of 3% thiourea in 1 mol L^− 1 HCl solution at a flow rate of 0.5 mL min^− 1. A new method using a microcolumn packed with MWNTs as sorbent has been developed for the preconcentration of trace amount of Au prior to its determination by flame atomic absorption spectrometry. Parameters influencing the preconcentration of Au, such as pH of the sample, sample flow rate and volume, elution solution and interfering ions, have been examined and optimized. Under the optimum experimental conditions, the detection limit of this method for Au was 0.15 µg L^− 1 with an enrichment factor of 75, and the relative standard deviation (R.S.D) was 3.1% at the 100 µg L^− 1 Au level. The method has been applied for the determination of trace amount of Au in geological and water samples with satisfactory results.     

Displacement-dispersive liquid-liquid microextraction coupled with graphite furnace atomic absorption spectrometry for the selective determination of trace silver in environmental and geological samples

A novel displacement-dispersive liquid-liquid microextraction method was developed for the selective determination of trace silver in complicated samples by graphite furnace atomic absorption spectrometry. This method involves two steps of dispersive liquid-liquid microextraction (DLLME). Firstly, copper ion reacted with diethyldithiocarbamate (DDTC) to form Cu-DDTC complex and extracted with DLLME procedure using carbon tetrachloride (extraction solvent) and methanol (dispersive solvent); then, the sedimented phase was dispersed into the sample solution containing silver ion with methanol and another DLLME procedure was carried out. Because the stability of Ag-DDTC is larger than that of Cu-DDTC, Ag⁺ can displace Cu²⁺ from the pre-extracted Cu-DDTC and thus the preconcentration of Ag⁺ was achieved. Potential interference from co-existing transition metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu²⁺ from Cu-DDTC complex. The tolerance limits for the co-existing ions were increased by a long way compared with conventional DLLME. Under the optimal conditions, the limit of detection was 20 ng L⁻¹ (3σ) for silver with a sample volume of 5.0 mL, and an enhancement factor of 72 was achieved. The proposed method was successfully applied to determine of trace silver in some environmental and geological samples with satisfactory results.     

Dispersive liquid-liquid microextraction followed by gas chromatography-mass spectrometry for the determination of nitro musks in surface water and wastewater samples

A new, simple, fast and high sensitive analytical method based on dispersive liquid-liquid microextraction (DLLME) followed by gas chromatography-mass spectrometry (GC-MS) for the simultaneous determination of nitro musks in surface water and wastewater samples is presented. Different parameters, such as the nature and volume of both the extraction and disperser solvents and the ionic strength and pH of the aqueous donor phase, were optimized. Under the selected conditions (injection of a mixture of 1 mL of acetone as disperser solvent and 50 μL of chloroform as extraction solvent, no salt addition and no pH adjustment) the figures of merit of the proposed DLLME-GC-MS method were evaluated. High enrichment factors, ranging between 230 and 314 depending on the target analyte, were achieved, which redound to limits of detection in the ng L⁻¹ range (i.e., 4-33 ng L⁻¹). The relative standard deviation (RSD) was below 5% for all the target analytes. Finally, the recoveries obtained for different water samples of diverse origin (sea, river, irrigation channel and water treatment plant) ranged between 87 and 116%, thus showing no matrix effects.     

浮动液滴固化分散液相微萃取-火焰原子吸收光谱法测定环境样品中的镉

建立了以十一醇为萃取剂,吡咯烷二硫代甲酸铵(APDC)为螯合剂的浮动液滴固化分散液相微萃取-火焰原子吸收光谱法(DLLME-SFO-FAAS)测定环境样品中痕量镉的分析方法;优化了分散剂、萃取剂的类型和体积,考察了溶液pH值、APDC浓度以及萃取温度和时间对萃取效率的影响.结果表明,该法检出限(3σ)为0.14μg/L...     

Separation/preconcentration and determination of vanadium with dispersive liquid-liquid microextraction based on solidification of floating organic drop (DLLME-SFO) and electrothermal atomic absorption spectrometry

A novel dispersive liquid-liquid microextraction based on solidification of floating organic drop (DLLME-SFO) for separation/preconcentration of ultra trace amount of vanadium and its determination with the electrothermal atomic absorption spectrometry (ETAAS) was developed. The DLLME-SFO behavior of vanadium (V) using N-benzoyl-N-phenylhydroxylamine (BPHA) as complexing agent was systematically investigated. The factors influencing the complex formation and extraction by DLLME-SFO method were optimized. Under the optimized conditions: 100 μL, 200 μL and 25 mL of extraction solvent (1-undecanol), disperser solvent (acetone) and sample volume, respectively, an enrichment factor of 184, a detection limit (based on 3S_b/m) of 7 ng L⁻¹ and a relative standard deviation of 4.6% (at 500 ng L⁻¹) were obtained. The calibration graph using the preconcentration system for vanadium was linear from 20 to 1000 ng L⁻¹ with a correlation coefficient of 0.9996. The method was successfully applied for the determination of vanadium in water and parsley.     

原位衍生分散液相微萃取-气相色谱-质谱快速测定水中的四溴双酚A

通过研究萃取剂、分散剂的种类和体积,KHCO3用量,衍生剂乙酸酐的用量和萃取时间对萃取效率的影响,建立了原位衍生分散液相微萃取-气相色谱质谱联用测定水中四溴双酚A的方法.方法线性范围:0.5～ 100 μg/L,检出限:0.1μg/L;RSD:5.4％ (n =5).将该方法用于环境水样的测定,加标回收率:53.5％ ...     

Single drop microextraction combined with graphite furnace atomic absorption spectrometry for determination of lead in biological samples

Single drop microextraction combined with graphite furnace atomic absorption spectrometry is introduced for the determination of trace lead in water samples. A drop of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) dissolved in benzene was held at the tip of a microsyringe and immerged into the sample solution which was stirred, the solvent drop interacts with the sample solution, and the analyte was extracted into the drop and concentrated. After extracting for a period of time, the drop was retracted into the microsyringe and directly injected into graphite furnace for GFAAS determination of Pb. Several factors affecting the extraction efficiency, such as pH of sample solution, drop volume, stirring rate and extraction time, were optimized. Under the optimized conditions, an enhancement factor of 16 was achieved, and the detection limits for Pb were 25 ng L⁻¹. The relative standard deviation for seven replicate determination of 10 ng mL⁻¹ Pb was 6.1%. The method was applied to determine trace Pb in biological samples with satisfactory results. Correspondence: Pei Liang, Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P.R. China