Method for the determination of cadmium, lead, nickel, cobalt and copper in seafood after dispersive liquid–liquid micro-extraction

Determination of Ultra-Trace Cobalt in Water Samples Using Dispersive Liquid-Liquid Microextraction Followed by Graphite Furnace Atomic Absorption Spectrometry

A novel method for the determination of ultra-trace cobalt by dispersive liquid–liquid microextraction (DLLME) coupled with graphite furnace atomic absorption spectrometry has been developed. It is based on the color reaction of Co²⁺ with 2-(5-bromo-2-pyridylazo)-5-dimethylaminoaniline (5-Br-PADMA) in a Britton–Robinson buffer solution at pH 6.0 to form stable hydrophobic chelates, which were separated and enriched by DLLME with 1,2-dichloroethane (CH₂ClCH₂Cl) as extraction and acetonitrile (CH₃CN) as a dispersive solvent. The sedimented phase containing the chelates is then determined with GFAAS. Parameters that affect extraction efficiency, such as types and volumes of extraction and disperser solvents, pH of sample solution, extraction time, concentration of the chelating agent 5-Br-PADMA, and salt effect, were investigated. Under optimal conditions, the calibration graph was linear over the range 0.05–1.0 ng/mL, with a correlation coefficient of 0.9922 and a detection limit of 0.03 ng/mL. Preconcentration factor (PF) is calculated as the ratio of the aqueous solution volume (5 mL) to that of the organic phase volume (40 μL), and enrichment factor (EF) is calculated as the ratio of the slopes of the calibration graphs obtained with and without DLLME for 5.0 mL of sample solution, which were 120 and 112.5, respectively. The extraction efficiency, calculated by EF/PF·100, was 93.8%. The relative standard deviation (RSD) at the 0.5 ng/mL Co²⁺ level was 3.8% (n = 6). The method has been applied to the determination of trace cobalt in water samples with satisfactory results.

Strategies of dispersive liquid-liquid microextraction for coastal zone environmental pollutant determination

Coastal zone means the interface of land and sea, and therefore, environmental pollutants steaming from land-based activities (like manufactories) and sea-based activities (like shipping) are all existing in coastal zone. These pollutants usually have characteristics of low residues, complicated matrices, easy accumulation and so on, causing difficulty to detect coastal pollutants quickly and sensitively. It is imperative to perform effective sample preparation prior to instrumental analysis. Dispersive liquid-liquid microextraction (DLLME) has attracted significant research interest for sample preparation, owing to its high enrichment ability, low reagent/sample consumption, and wide analyte/matrix applicability, as well as robustness, simplicity, rapidity and inexpensiveness. Herein, we comprehensively review the recent advancements of DLLME technology and its analytical parameters including enrichment principles, extraction modes, and practical application; the emphasis is on novel mode-construction and representative coastal-environmental pollutants extraction. Construction strategies are highlighted by classifying DLLME into five major modes, according to extractant's types, including normal ones, low density solvents, ionic liquids, deep eutectic solvents and others. The coupling of DLLME with other extraction techniques like solid-phase extraction is also briefly introduced. The strengths and weaknesses of each strategy and its rationality are also elaborated. In addition, some typical applications of the different DLLME modes for the determination of organic compounds and heavy metals in coastal water, sediment, soil, and biota are summarized. The increasingly concerned green aspects and instrumentation of DLLME are presented, and finally, the challenges and perspectives of the DLLME for environmental analysis are proposed.

Multivariate optimization of a dispersive liquid-liquid microextraction method for determination of copper and manganese in coconut water by FAAS

In this study, multivariate methodologies were applied in the optimization of a dispersive liquid-liquid microextraction (DLLME) method, aiming at the determination of Cu and Mn in coconut water samples by flame atomic absorption spectrometry. Some extractors (chloroform and CCl₄), dispersants (ethanol, methanol and acetonitrile) and complexing agents (5-Br-PADAP and Dithzone) were previously tested in the extraction. A mixture design was used to optimize the component proportions formed by chloroform (10%), acetonitrile (76%), and 0.020% 5-Br-PADAP solution (14%). Doehlert design optimized the variables pH, NaCl, and buffer amounts for the extraction of both metals. The following analytical characteristics, respectively for Cu and Mn, were accessed: limit of quantification (4.83 and 3.32 µg L^-1), enrichment factors (11 and 8 fold), and precision (6.6 and 6.0% RSD, n = 10). Addition/recovery tests of the analytes allowed to find values in the range of 96.5-120% for Cu and 99-107% for Mn.

Multivariate optimization of ultrasound-assisted liquid-liquid microextraction based on two solvents for cadmium preconcentration prior to determination by flame atomic absorption spectrometry

A method based on ultrasound-assisted emulsification liquid-liquid microextraction (USAEME) for cadmium determination by flame atomic absorption spectrometry (FAAS) was developed in this work. USAEME is based on the use of the mixture of 1,2-dichloroethane and trichloroethylene as an acceptor phase, 2-(2-bromo-5-pyridylazo)-5(diethylamino)phenol (Br-PADAP) as a chelating reagent, and ethanol as a dispersive solvent. The composition of the extraction and dispersive solvents, the volume of the extraction solvent, pH, and the sonication time were optimized using the multivariate strategy. The limits of detection and quantification calculated under optimum conditions were, respectively, 0.39 and 1.33 μg L-1, and the obtained enrichment factor was 21. The accuracy was tested by the analysis of certified reference materials. The method was applied to cadmium determination in bivalve mollusks, water, and urban wastewater from Pontal Bay, Bahia, Brazil. The proposed method is simple, fast, and efficient, and uses small amounts of organic solvents for the determination of cadmium.

Preconcentration and Determination of Trace Nickel and Cobalt in Milk-Based Samples by Ultrasound-Assisted Cloud Point Extraction Coupled with Flame Atomic Absorption Spectrometry

In this study, ultrasound-assisted cloud point extraction (UA-CPE) method was developed for the determination of Ni(II) and Co(II) in milk-based products. After extraction and preconcentration, the Ni(II) and Co(II) contents of samples were determined by flame atomic absorption spectrometry (FAAS). After their complexation with hydroxy naphthol blue (HNB) in the presence of cationic surfactant, CTAB at pH 4.0, the Ni(II) and Co(II) were taken within the micellar phase of nonionic surfactant, TX-114. The micellar phase containing the analytes were diluted to a volume of 0.7 mL with 1.0-mol/L HNO₃ in ethanol to reduce its viscosity and to facilitate sample treatment and then was analyzed by FAAS. The various analytical parameters affecting UA-CPE efficiency were investigated. The analytical features obtained after optimization are as follows: limits of detection are 0.56 and 0.78 μg/L; sensitivity enhancement factors are 48.6 and 53.9; the calibration curves were linear 3-180 and 2-160 μg/L for Co(II) and Ni(II), respectively, after preconcentration of 50-fold. The precision (as RSD%) between 1.8-3.6% and 2.2-3.8% (25 and 100 μg/L, n = 5) for Ni(II) and Co(II), respectively. The accuracy was statistically verified by analysis of two certified reference material samples (CRMs), including recovery studies after spiking. The method was applied to the analysis of milk-based samples with satisfied results.

Persistent sample circulation microextraction combined with graphite furnace atomic absorption spectroscopy for trace determination of heavy metals in fish species marketed in Kermanshah, Iran, and human health risk assessment

BACKGROUND

Persistent sample circulation microextraction (PSCME) combined with graphite furnace atomic absorption spectrometry (GFAAS) was developed as a high pre-concentration technique for the determination of heavy metals in fish species. In this method, a few microliters of organic solvent (40.0 µL carbon tetrachloride) was transferred to the bottom of a conical sample cup. Then 10.0 mL of aqueous solution was transformed to fine droplets while passing through the organic solvent. At this stage, metal-ligand hydrophobic complex was extracted into the organic solvent. After extraction, 20 µL of extraction solvent was injected into the graphite tube using an auto-sampler.

RESULTS

Under optimal conditions, enrichment factors and enhancement factor were in the range of 180-240 and 155-214, respectively. The calibration curves were linear in the range of 0.03-200 µg kg^-1 and the limits of detection (LODs) were in the range of 0.01-0.05 µg kg^-1 . Repeatability (intra-day) and reproducibility (inter-day) for 0.50 µg L^-1 Hg and 0.10 µg L^-1 Cd and Pb were in the range of 3.1-4.2% (n = 7) and 4.3-6.1% (n = 7), respectively.

CONCLUSION

Potential human health risk assessment was conducted by calculating estimated weekly intake (EWI) of the metals from eating fish and comparison of these values with provisional tolerable weekly intake (PTWI) values. EWI data for the studied metals through fish consumption were lower than the PTWI values. © 2017 Society of Chemical Industry.

Dispersive liquid-liquid microextraction based on solidification of floating organic drop for preconcentration and determination of trace amounts of copper by flame atomic absorption spectrometry

A novel, simple, rapid, sensitive, inexpensive and environmentally friendly dispersive liquid-liquid microextraction method based on the solidification of a floating organic drop (DLLME-SFO) was developed for the determination of copper by flame atomic absorption spectrometry (FAAS). N-o-Vanillidine-2-amino-p-cresol was used as a chelating ligand and 1-undecanol was selected as an extraction solvent. The main parameters affecting the performance of DLLME-SFO, such as sample pH, volume of extraction solvent, extraction time, concentration of the chelating ligand, salt effect, centrifugation time and sample volume were investigated and optimized. The effect of interfering ions on the recovery of copper was also examined. Under the optimum conditions, the detection limit (3σ) was 0.93μgL^-1 for Cu using a sample volume of 20mL, yielding a preconcentration factor of 20. The proposed method was successfully applied to the determination of Cu in tap, river and seawater, rice flour and black tea samples as well as certified reference materials.