Switchable-hydrophilicity solvent-based liquid-phase microextraction in an on-line system: Cobalt determination in food and water samples.

An on-line system employing switchable-hydrophilicity solvent-based liquid-phase microextraction (SHS-LPME) is described in this work. The method is based on the preconcentration of the species formed between cobalt and the reagent 1-nitroso-2-naphthol (NN), with subsequent detection by digital image colorimetry. The system's operation begins with the on-line mixture of sample, switchable solvent, and an alkaline agent in a reaction coil. Then the mixture is transported to an extraction chamber. The introduction of a proton donor leads to the passage of the solvent to its hydrophobic form, which allows phase separation. The rich phase is then directed to a glass tube, where detection is performed. Octanoic acid, sodium carbonate, and sulfuric acid were used as the extraction solvent, the alkaline agent, and the proton donor, respectively. Under optimized conditions, the method presented a detection limit of 0.8 µg L-1 and an enrichment factor of 41. The precision obtained was 4.8% (20 µg L-1). The accuracy of the method was tested by the analysis of Tomato Leaves certified reference material (NIST 1573a). The method was applied to the determination of cobalt in food, dietary supplements, and water samples. The method is presented as a green alternative and very accessible to the determination of cobalt in the analyzed samples.

In-syringe dispersive liquid-liquid microextraction.

Dispersive liquid-liquid microextraction (DLLME) has recently been widely used in the separation and preconcentration of various chemical species. Among the various approaches using DLLME are systems that use a syringe as an extraction environment. In this review, details of some methods that use this approach are presented. The ways to promote dispersion, analytical characteristics, and the advantages and disadvantages of the methods, among other aspects, are discussed critically. Finally, some trends in the use of in-syringe microextraction systems are described.

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.

A novel direct-immersion single-drop microextraction combined with digital colorimetry applied to the determination of vanadium in water.

In this study, a method based on direct-immersion single-drop microextraction was developed for the determination of vanadium in water. The detection system uses digital images obtained directly from the solvent drop after the sorption of V(V). The extraction solvent used was the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM][PF6]). The images were obtained directly from the solvent drop, with the aid of a camera. The digital images were stored, and the RGB (red, green, and blue) data were obtained. The data collected by the red channel were used to construct the analytical curve since it showed higher sensitivity compared with green and blue channels. Under optimized conditions, the method presented an enrichment factor of 50 and a limit of detection of 0.6 µg L-1 for 3.5 mL sample volume. The limit of quantification and the relative standard deviation (50.0 µg L-1) obtained were 1.8 µg L-1 and 4.8%, respectively. Certified reference material (Plankton) was used to assess the accuracy of the method. The simple, fast, efficient, and low-cost procedure was successfully applied to the determination of V(V) in water samples. The proposed method is also following the principles of green chemistry since it uses minimal volumes of samples, reagents, and solvents and yields a small amount of waste.

A novel strategy based on in-syringe dispersive liquid-liquid microextraction for the determination of nickel in chocolate samples.

In this work, a novel approach was developed to perform dispersive liquid-liquid microextraction using a rapid pressure variation to disperse the extraction solvent in an aqueous medium. A glass syringe was used to produce an environment subject to a rapid pressure difference. The element used as a model was nickel and the approach was called pressure variation in-syringe dispersive liquid-liquid microextraction (PV-IS-DLLME). The extraction solvent used was 1-butyl-3-methylimidazolium hexafluorophosphate, and ammonium pyrrolidine dithiocarbamate was the complexing reagent. The variables pH, solvent volume, amount of complexing agent, extraction time and syringe volume were studied by a factorial 25-1 fractional design. All variables were significant. However, the two least significant, amount of complexing agent (50.0 µL) and syringe volume (20.0 mL) were fixed at their optimum levels, according to the generated Pareto chart. A Doehlert matrix was studied for the variables volume of solvent, pH and extraction time to obtain optimal levels of these factors, and the contour plots showed the following critical values: 120.0 µL, 2.0 and 60.0 s respectively. The developed method presented limits of detection and quantification of 0.1 and 0.3 mg kg-1, an enrichment factor of 17 and a precision of 4.8% (100.0 µg L-1). The developed method was applied to the analysis of samples of powdered chocolate and certified reference material.

Ultrasound-Assisted Emulsification Microextraction in an Online System for Determination of Cadmium in Water and Tea Samples.

In this work, a method using ultrasound-assisted emulsification microextraction (USAEME) without the use of ligands in an online system for preconcentration and determination of cadmium was developed. The method was based on the preconcentration of cadmium by USAEME, employing trichloroethylene as the extraction solvent, and subsequent retention of the rich phase in a mini-column packed with silica gel. The extracted metal was determined by flame atomic absorption spectrometry. The parameters that affect the extraction of cadmium were optimized using the univariate method. Under optimized conditions, the method presented a limit of detection of 0.17 µg/L, a limit of quantification of 0.57 µg/L, an enrichment factor of 56, and a consumptive index of 0.18 mL/min. The accuracy of the method was tested by analyzing the certified reference material, National Institute of Standards and Technology (NIST) 1573 (tomato leaves). The determination of Cd in water (drinking water, bottled water, river water, and seawater) and tea (black and green tea) samples was also performed using the proposed method. The method is simple, efficient, and eco-friendly because it requires low consumption of an organic solvent.

Homogeneity study of a corn flour laboratory reference material candidate for inorganic analysis.

In this work, a homogeneity study of a corn flour reference material candidate for inorganic analysis is presented. Seven kilograms of corn flour were used to prepare the material, which was distributed among 100 bottles. The elements Ca, K, Mg, P, Zn, Cu, Fe, Mn and Mo were quantified by inductively coupled plasma optical emission spectrometry (ICP OES) after acid digestion procedure. The method accuracy was confirmed by analyzing the rice flour certified reference material, NIST 1568a. All results were evaluated by analysis of variance (ANOVA) and principal component analysis (PCA). In the study, a sample mass of 400mg was established as the minimum mass required for analysis, according to the PCA. The between-bottle test was performed by analyzing 9 bottles of the material. Subsamples of a single bottle were analyzed for the within-bottle test. No significant differences were observed for the results obtained through the application of both statistical methods. This fact demonstrates that the material is homogeneous for use as a laboratory reference material.

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

A method using dispersive liquid-liquid micro-extraction (DLLME) and detection by inductively coupled plasma optical emission spectroscopy (ICP-OES) was developed for the determination of trace elements in seafood samples. The procedure allowed the simultaneous determination of Cd(II), Pb(II), Ni(II) Cu(II) and Co(II) after pre-concentration using sodium diethyldithiocarbamate (DDTC) as a chelating agent. Under optimised conditions, the method had a limit of detection (LOD) of 0.03, 0.11, 0.12, 0.18 and 0.12 µg l(-1) for Cd(II), Pb(II), Ni(II) Cu(II) and Co(II), respectively. The following enrichment factors were obtained: 16 (Cd), 34 (Pb), 20 (Ni) 34 (Cu) and 12 (Co). The procedure was applied for the determination of these elements in seafood (shrimp, mussel, bass and mullet) samples. The method is simple, efficient and easy to perform for the simultaneous determination of elements in seafood samples by ICP-OES.

A new method for preconcentration and determination of mercury in fish, shellfish and saliva by cold vapour atomic absorption spectrometry.

The development of a method using solid phase extraction for preconcentration and determination of mercury by cold vapour atomic absorption spectrometry is described. Hg (II) ions are sorbed on a minicolumn packed with Amberlite XAD-4 sorbent functionalised with 2-(2'-benzothiazolylazo)-p-cresol (BTAC). Then, a reducing solution was used for desorption and the transport of the analyte for subsequent detection. The assay presented a limit of detection of 0.011 µg L⁻¹ (0.011 µg g⁻¹, for solid samples), a limit of quantification of 0.038 µg L⁻¹ (0.038 µg g⁻¹, for solid samples), a precision of 0.50% (1.000 µg L⁻¹ Hg solution) and an enrichment factor of 46. The proposed method was applied to the determination of mercury in human saliva (0.055-0.200 µg L⁻¹). The following seafood collected in Todos os Santos Bay, Brazil was also analysed: bass (0.169-0.195 µg g⁻¹), mullet (0.043-0.361 µg g⁻¹), shrimp (0.075-0.374 µg g⁻¹) and mussel (0.206-0.397 µg g⁻¹).

Spectrophotometric determination of mercury in water samples after preconcentration using dispersive liquid-liquid microextraction.

A simple method for the determination of mercury in water samples after preconcentration using dispersive liquid-liquid microextraction is described. The procedure is based on the extraction of mercury in the form of a complex and its subsequent determination by spectrophotometry. The complex is formed between Hg(II) and 2-(2-benzothiazolylazo)-p-cresol. The detection at 650 nm is performed directly in the metal-rich phase, which is spread on a triacetylcellulose membrane. The method eliminates the need to use a cuvet or large quantities of samples and reagents. The parameters that influence the preconcentration were studied, and the analytical characteristics were determined. The enrichment factor and the consumptive index for this method were 64 and 0.16 mL, respectively. The LOD (3.3 microg/L) and LOQ (11.1 microg/L) were also determined. The accuracy of the method was tested by the determination of mercury in certified reference materials BCR 397 (Human Hair) and SRM 2781 (Domestic Sludge). The method was applied to the determination of mercury in samples of drinking water, sea water, and river water.

A preconcentration procedure for the determination of cadmium in biological material after on-line cloud point extraction.

In this paper, a method involving on-line preconcentration with cloud point extraction for the determination of cadmium in biological samples is presented. The procedure is based on the sorption of micelles containing Cd(II) ions and the reagent 4-(5'-bromo-2'-thiazolylazo)orcinol (Br-TAO) in a minicolumn packed with polyester. The surfactant Triton X-114 was used in the formation of micelles. After sorption, the Cd(II) ions were desorbed from the minicolumn with acid eluent and determined by flame atomic absorption spectrometry. Parameters influencing the cloud point extraction were studied. The method showed a detection limit of 0.5 µg l(-1) and an enhancement factor of 27. The accuracy was tested by determination of cadmium in certified reference materials (spinach leaves 1570a and tomato leaves 1573a) from the National Institute of Standards and Technology.

Synthesis and application of a new thiazolylazo reagent for cloud point extraction and determination of cobalt in pharmaceutical preparations.

The synthesis and characterization of the reagent 2-(5-bromothiazolylazo)-4-chlorophenol and its application in the development of a preconcentration procedure for cobalt determination using flame atomic absorption spectrometry after cloud point extraction is presented. This procedure is based on cobalt complexing and entrapment of the metal chelates into micelles of a surfactant-rich phase of Triton X-114. The preconcentration procedure was optimized by using a response surface methodology through the application of the Box-Behnken matrix. Under optimum conditions, the procedure determined the presence of cobalt with an LOD of 2.8 microg/L and LOQ of 9.3 microg/L. The enrichment factor obtained was 25. The precision was evaluated as the RSD, which was 5.5% for 10 microg/L cobalt and 6.9% for 30 microg/L. The accuracy of the procedure was assessed by comparing the results with those found using inductively coupled plasma-optical emission spectrometry. After validation, the procedure was applied to the determination of cobalt in pharmaceutical preparation samples containing cobalamin (vitamin B12).

Determination of lead and manganese in biological samples and sediment using slurry sampling and flame atomic absorption spectrometry.

A procedure was developed for the determination of lead (Pb) and manganese (Mn) using slurry sampling. The two elements were detected using flame atomic absorption spectrometry with a slotted tube atom trap. Slurries were prepared by adding nitric acid solution (0.30%, w/v) to a powdered sample (0.10 g). After homogenization by ultrasonic bath for 15 min, the slurries were introduced directly into the detection equipment. Some conditions of the procedure were evaluated, such as acid concentration, presence of surfactants, and sonication time. Under optimized conditions, the LODs and LOQs achieved were 0.8 and 2.6 microg/g for Pb and 0.5 and 1.6 microg/g for Mn, respectively. The precision obtained varied between 3.1 and 5.8% (Mn), and 2.6 and 5.4% (Pb) for slurries of shrimp and sediment. The analytical curves were established using aqueous standards in nitric acid solutions. The accuracy of the method was assessed through the determination of Pb and Mn in the following certified reference materials: ERM-CE 278 (mussel tissue), CRM 397 (human hair), and SRM 1646a (estuarine sediment). The proposed procedure was successfully applied to the determination of Pb and Mn in six samples of shrimp powder, seasoning, and river sediment. The levels of Mn detected varied from 2.2 to 71.3 microg/g; Pb was detected in only one sediment sample (4.3 microg/g).

Synthesis of a new solid-phase extractor and its application to preconcentration and determination of lead in water samples.

A procedure for preconcentration and determination of lead in water is described. The method is based on the sorption of Pb(II) in a minicolumn packed with a functionalized sorbent and subsequent elution with acidic solution. The determination of lead content in the eluate was carried out using flame atomic absorption spectrometry. The sorbent was prepared by immobilization of the ligand 4-(5'-bromo-2'-thiazolylazo)orcinol on polystyrene-divinylbenzene through an azo spacer. Diazotization and coupling reactions were used for synthesis of the sorbent. Some variables affecting the preconcentration were optimized using a full factorial design. Under optimized conditions, the method presented a detection limit of 0.5 microg/L and enrichment factor of 36 for a sample volume of 25 mL. The accuracy of the method was tested by the determination of lead in a standard reference material (National Institute of Standards and Technology 1643d Fresh Water). The proposed procedure was applied to the determination of lead in samples of natural and drinking waters.

Thermospray generation directly into a flame furnace--an alternative to improve the detection power in atomic absorption spectrometry.

Recent developments and applications in the production of thermosprays directly into flame furnaces to improve the analytical sensitivity in atomic absorption spectrometry are reviewed in this manuscript. Principles, characteristics, instrumentation, and applications of this analytical technique for trace elements determination in several matrices are discussed. The use of preconcentration procedures to allow low detection limits for ultra-trace levels using TS-FF-AAS is presented and current perspectives and future trends of this technique are also discussed.

Determination of cadmium and lead in human biological samples by spectrometric techniques: a review.

The analysis of human biological samples, such as blood, urine, nails, and hair, is generally used for the verification of human exposure to toxic metals. In this review, various spectrometric methods for the determination of cadmium and lead in biological samples are discussed and compared. Several spectrometric techniques are presented and discussed with respect to various characteristics such as sensitivity, selectivity, and cost. Special attention is drawn to the procedures for digestion prior to the determination of cadmium and lead in hair, nails, blood, and urine.

An online preconcentration system for the determination of uranium in water and effluent samples.

Amberlite XAD-4 resin functionalized with ß-nitroso-α-naphthol was applied to an online system for the preconcentration and determination of uranium. U (VI) ions were retained on the minicolumn at an appropriate pH and then desorbed with acid solution. The amount of uranium in the eluate was measured spectrophotometrically at 650 nm using Arsenazo III as a colorimetric reagent. The limit of detection and the preconcentration factor were 1.8 µg L(-1) and 10, respectively. The chemical and flow variables affecting the preconcentration were studied. The influence of several ions on the system was also investigated. The method was successfully applied for the evaluation of uranium in water and in effluent samples.

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 microg 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.

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 microg g(-1) (Cu) and 0.4 microg g(-1) (Ni). The precision for 10 replicate measurements of 75 microg L(-1) Cu or Ni was 6.4 and 1.0, respectively. The method has been successfully applied to the analysis of food samples.

Flow injection preconcentration system using a new functionalized resin for determination of cadmium and nickel in tobacco samples.

A solid-phase extraction method combined with flow injection (FI) on-line flame atomic absorption spectrometry (FAAS) for the determination of cadmium and nickel in tobacco samples is presented. The 2-aminothiophenol functionalized Amberlite XAD-4 (AT-XAD) resin was synthesized by covalent coupling of the ligand with the copolymer through a methylene group. A minicolumn packed with AT-XAD was connected into the automated on-line preconcentration system. Elution of metal ions from minicolumn can be made with 0.50 mol L(-1) hydrochloric acid solution. With a consumption of 21.0 mL of sample solution, detection limits (3 s) of 0.3 (Cd) and 0.8 microg L(-1) (Ni) were achieved at a sample throughput of 18 h(-1). Enrichment factors (EF) of 99 (cadmium) and 43 (nickel) were obtained compared with the slope of the linear portion of the calibration curves before and after preconcentration. The contents of Cd and Ni in a certified reference material (NIST 1570a, spinach leaves) determined by the present method was in good agreement with the certified value. The developed procedure was also successfully applied to the determination of Cd and Ni in local tobacco samples.