Removal of molybdenum using silver nanoparticles from water samples: Particle swarm optimization–artificial neural network

In this study, a simple and fast method for preconcentration and determination of trace amount of molybdenum from water samples was developed by silver nanoparticles based solid-phase extraction method and UV–vis spectrophotometry. Hybrid of artificial neural network–particle swarm optimization (ANN–PSO) has been used to develop predictive models for simulation and optimization of solid phase extraction method. Under the optimum conditions, the detection limit and relative standard deviation were 11 μg L⁻¹ and <3.9%, respectively. The pre-concentration factor of this method was 50. The method was applied to preconcentration and determination of molybdenum from water samples.     

Cadmium ion-selective sorbent preconcentration method using ion imprinted poly(ethylene glycol dimethacrylate-co-vinylimidazole)

The present study focuses on the preparation of an Cd²⁺-imprinted poly(ethylene glycol dimethacrylate-co-vinylimidazole) for selective extraction/preconcentration of Cd²⁺ ions from aqueous solution, with further determination by FAAS using a flow system. Sorbent extraction/preconcentration system was optimized by using chemometric tools (factorial design and Doehlert matrix). Under optimized conditions, the method presented a limit of detection of 0.11 μg L^?1 and linear analytical curve from 1.0 up to 50.0 μg L^?1 (r = 0.993). The preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were found to be 38.4, 0.39 mL and 14.3 min^?1, respectively. The selectivity coefficient of ion imprinted polymer was compared with the selectivity coefficient of NIP (non-imprinted polymer) for the Cd²⁺/Pb²⁺, Cd²⁺/Cu²⁺ and Cd²⁺/Zn²⁺ binary mixtures, where the respective values of relative selectivity coefficient (k′) of 157.5, 4.44 and 1.38 were obtained. The proposed method was successfully applied for cadmium determination in different types of water samples, urine and certified reference material (Lobster Hepatopancreas).     

Silver nanoparticle-based spectrophotometric method for quantification of nile blue A in river water

A novel and sensitive spectrophotometric method is developed for the determination of nanomolar level of nile blue A in water samples based on its catalytic effect of silver nanoparticles on the oxidation of nile blue A by hexacyanoferrate (III) in acetate-acetic acid medium and at 25 °C. The absorbance is measured at 595.5 nm with the fixed-time method. The optimization of the operating conditions regarding concentration of the reagents, temperature and interferences is also investigated. The calibration curve is linear over the concentration range between 85 and 2000 nM of nile blue A with good precision and accuracy. The detection limit of the method is down to 54. The relative standard deviation for a standard solution of 100.0 nM of nile blue A is 1.63% (n = 10). The proposed method provides a highly sensitive, selective and relatively rapid assay for nile blue A at nanomolar level without any pre-concentration and separation step. The method was applied to the determination of nile blue A in river water samples.     

Determination of sulfonylurea herbicides in soil samples via supercritical fluid extraction followed by nanostructured supramolecular solvent microextraction

The present work describes a sensitive procedure for extraction and determination of three sulfonylurea herbicides (metsulfuron-methyl, bensulfuron-methyl and chlorsulfuron) in water samples using supramolecular solvent microextraction. A supramolecular solvent with a nano structure made up of decanoic acid assemblies dispersed in tetrahydrofuran and water was proposed. Also, a supercritical fluid extraction coupled with supramolecular solvent microextraction was applied for extraction and determination of ultra-trace amounts of sulfonylurea herbicides in soil samples. A Taguchi orthogonal array experimental design with an OA₁₆ (4⁵) matrix was employed to optimize the supercritical fluid extraction conditions. In supercritical fluid extraction–supramolecular solvent microextraction procedure, a mixture of decanoic acid and the SFE collecting solvent (tetrahydrofuran) was added to water for supramolecular solvent formation. The effective parameters on the supramolecular solvent microextraction efficiency were studied and optimized using two different optimization methods: one variable at a time and face centered design. Under the optimum conditions, linear dynamic ranges varied within 0.1–5 mg kg⁻¹ (0.9978 ≤ R² ≤ 0.9987) and 0.5–100 μg L⁻¹ (0.9973 ≤ R² ≤ 0.9995) for all of the sulfonylurea herbicides in the supercritical fluid extraction–supramolecular solvent microextraction and supramolecular solvent microextraction, respectively. The intraday (n = 5) and interday standard deviations were calculated by extracting the SUHs from water and soil samples through supramolecular solvent microextraction and supercritical fluid extraction–supramolecular solvent microextraction. Interday RSDs% lower than 7.1% and intraday RSDs% lower than 3.8% were obtained. Limits of detection, based on a S/N ratio of 3, were 0.5 μg L⁻¹ and 0.7 mg kg⁻¹ for supramolecular solvent microextraction and supercritical fluid extraction–supramolecular solvent microextraction, respectively.     

Preconcentration and speciation of vanadium by three phases liquid–liquid microextraction prior to electrothermal atomic absorption spectrometry

We developed a new method three phase liquid–liquid microextraction (TPLLME) for simultaneous speciation of vanadium. This efforts were launched to know the species and aqueous transport chemistry of the binary V-(1-(2-Pyridylazo)-2-naphthol) complex across the interface of the three phases. Various analytical parameters were optimized. The limit of detection (LOD) was 0.034 μg L⁻¹ and 0.028 μg L⁻¹ for V(V) and V(IV) with preconcentration factor of 100. Relative standard deviation (RSD) was found 4.32% for V(V) and 4.22% for V(IV). The proposed method was applied to species of vanadium successfully in sea water and tap water samples. The method was also applied to certified reference material and food samples for total vanadium determination.     

Synthesis and adsorption studies of novel hybrid mesoporous copolymer functionalized with protoporphyrin for batch and on-line solid-phase extraction of Cd2+ ions

A hybrid copolymer [poly(ethylene glycol dimethacrylate-co-protoporphyrin)-silica], synthesized by free radical copolymerization and sol–gel process was evaluated as novel adsorbent for solid-phase extraction of Cd²⁺ ions. Characterization of hybrid polymer was performed by FTIR, SEM and surface area analyzes. Adsorption isotherms built at pH 8.9 were very well adjusted (R² = 0.9982) to hybrid non-linear Langmuir–Freundlich model for two sites, indicating the existence of different affinity constants for binding sites, which was confirmed by Scatchard plot. The estimated maximum adsorption capacity was found to be 8.28 mg g^?1. The adsorption kinetics data also corroborated to the isotherm, where the Cd²⁺ ions adsorption followed the pseudo-second-order kinetic (R² = 0.998). The on-line preconcentration procedure, optimized by means of factorial designs, was based on sample preconcentration (16 mL) at pH 8.9 through 50.0 mg of hybrid copolymer packed in mini-column at 8.0 mL min^?1 flow rate. The on-line desorption of Cd²⁺ ions towards the FAAS detector was carried out in countercurrent at 5.0 mL min^?1 flow rate using 0.8 mol L^?1 HNO₃. Using the on-line preconcentration procedure, the maximum adsorption capacity determined from breakthrough curve was found to be 2.25 mg g^?1. Analytical curve ranged from 0.0 up to 50.0 μg L^?1 (r = 0.997), limit of detection of 0.27 μg L^?1, preconcentration factor of 38.4, sample throughput of 30 h^?1 and consumptive index of 0.41 mL, were achieved. The preconcentration method, very tolerable to several foreign ions, was successfully applied to the Cd²⁺ ions determination in water samples and cigarette sample. The accuracy was checked from analysis of certified reference materials.     

Nano-alumina coated with sodium dodecyl sulfate and modified with 4-(2-Pyridylazo) resorcinol for extraction of heavy metals in different matrixes

A green, novel and efficient solid phase extraction method based on the use of nano-alumina (nano-Al₂O₃) coated with sodium dodecyl sulfate (SDS) and modified with 4-(2-Pyridylazo) resorcinol (PAR) as a new adsorbent was developed for separation and preconcentration of trace amounts of Ni, Pb, Cu and Zn ions prior to determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). Under the optimum conditions (eluent: HNO₃, 4.0 mL, 3.0 mol L⁻¹; adsorbent: 0.8 g of nano-Al₂O₃, 40 mg of SDS, 8.6 mg of PAR; and sample: pH 6, flow rate 2.0 mL min⁻¹), adsorption capacity of nano-Al₂O₃-SDS-PAR, enrichment factors and limits of detection for the analytes were 8.7–12.9 mg g⁻¹, 125–250, and 0.12–0.71 μg L⁻¹, respectively. The proposed method presented excellent repeatability with relative standard deviations less than 1.6% (n = 10), and calculated calibration curves gave good level of linearity with correlation coefficient values between 0.989 and 0.999. Finally, the feasibility of the method was evaluated by extraction and determination of Ni, Pb, Cu and Zn ions in rice seed, apple juice, coriander, lettuce and tap water samples.     

Multiwalled carbon nanotube impregnated with tartrazine: Solid phase extractant for Cd(II) and Pb(II)

A solid phase extraction procedure has been presented by using multiwalled carbon nanotube impregnated with tartrazine for cadmium (Cd(II)) and lead (Pb(II)) ions. The influences of pH, flow rate, eluent and sample volume were investigated. No interference effects were observed from the alkaline, alkaline earth and some transition metals. The detection limits (LOD) were 0.8 and 6.6 μg L⁻¹ for Cd(II) and Pb(II), respectively. The preconcentration factor was 40. The validation of the procedure was controlled by the analysis of certified references materials. The procedure was applied to the determination of cadmium and lead in natural water and food samples.     

Combination of ACO-artificial neural network method for modeling of manganese and cobalt extraction onto nanometer SiO2 from water samples

In this study, modeling based on ant-colony optimization – artificial neural network have been employed to develop the model for simulation and optimization of nanometer SiO₂ for the extraction of manganese and cobalt from water samples. The pH, time, amount of SiO₂ nanoparticles and concentration of 1-(2-pyridylazo)-2-naphthol (PAN) were the input variables, while the extraction% of analytes was the output. Under the optimum conditions, the detection limits were 0.52 and 0.7 μg L^?1, for manganese and cobalt, respectively. The method was applied to the extraction of manganese and cobalt from water samples and one certified reference material.     

Synthesis,characterization and application of a chelating resin for solid phase extraction of some trace metal ions from water,sediment and tea samples

A new chelating resin, poly (2-thiozylmethacrylamide-co-divinylbenzene -co-2-acrylamido-2-methyl-1-propanesulfonic acid) was successfully prepared in the present work. Its composition, morphology, and properties were studied by Fourier transform infrared spectroscopy, scanning electron microscopy, elemental analysis, and thermogravimetric analysis. Several factors affecting the extraction of the metal ions including pH, the eluent type and concentration, flow rate, sample volume, and effect of interfering ions were investigated. The adsorption capacity of the resin for the elements studied was found in the range of 4.76–13.0 mg g⁻¹. A preconcentration factor of 150 was achieved at the optimum conditions. The limits of detection (3s/b) varied from 0.23 to 1.07 μg L⁻¹. The method validation was performed by analyzing certified reference materials (TMDA-70 Fortified lake water, SPS-WW1 Batch 111-Wastewater, RM 8704 Buffalo river sediment, GBW07605 Tea) and spiked water samples. The method was applied to separate and determine the trace levels of Cd(II), Ni(II), Co(II), Mn(II) and Pb(II) in the well water, river water, street sediment, and tea samples.     

Optimization of Cu(II)-ion imprinted nanoparticles for trace monitoring of copper in water and fish samples using a Box–Behnken design

We describe a nanoparticles ion-imprinted polymer (IIP) for the selective preconcentration of copper (II) ions. It was obtained by precipitation polymerization from 2-vinylpyridine (the functional monomer), ethylene glycol dimethacrylate (the cross-linker), 2,2′-azobisisobutyronitrile (the initiator), 2,9-dimethyl-1,10-phenanthroline (the copper-binding ligand) and nickel nitrate (the template ion) in acetonitrile solution. The IIP particles were characterized by Fourier Transformed Infra Red Spectroscopy (FTIR), thermogravimetric and differential thermal analysis, and by scanning electron microscopy. The optimization process was carried out using the Box–Behnken design (BBD). Effects of several factors such as solution pH for adsorption, amount of polymer, type, concentration and volume of eluent for extraction, as well as adsorption and desorption times were investigated. Under the optimum conditions (type and concentration of eluent, HCl 1.6 mol L^?1; volume of eluent, 6 mL; adsorption solution pH, 6.0; amount of polymer, 30 mg; adsorption time, 25 min; desorption time, 25 min), preconcentration factor of the proposed method was approximately 100. Under the optimized conditions, the detection limit was found to be 0.1 μg L^?1, while the relative standard deviation (RSD) for six replicate measurements was calculated to be <4%.     

Chemically modified carbon nanotubes as efficient and selective sorbent for enrichment of trace amount of some metal ions

Multi-walled carbon nanotubes (MWCNT) was oxidized and chemically functionalized by 3-hydroxy-4-((3-silylpropylimino) methyl) phenol (HSPIMP) and characterized with FT-IR technique. This new sorbent was used for enrichment and preconcentration of Cu²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Co²⁺, Fe³⁺ ions. Variables such as pH, amount of solid phase, eluting solution conditions (type, volume and concentrations) have significant effect on sorption and recoveries of analytes and the influence was optimized. At optimum value of conditions, the interference of other ions on understudy ions recoveries was investigated. The metal ions loaded on the solid phase via chelation with the new sorbent and subsequently efficiently eluted using 6 mL of 4 mol L^?1 HNO₃ solution. At each run, metal ions content was determined by flame atomic absorption spectrometry (FAAS). Relative standard deviation (N = 3) for determination of 0.2 μg mL^?1 of analytes was between 1.6 and 3.0%, while their detection limit was between 1.0 and 2.6 ng mL^?1 (3Sb, n = 10). The sorption capacity of HSPIMP–MWCNT for understudy ions was above 30 mg g^?1. The proposed method successfully applied for the extraction and determination of the understudy metal ions in different samples.     

Simultaneous preconcentration of Cd(II), Cu(II) and Pb(II) on Nano-TiO2 modified with 2-mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

Nano-TiO₂ modified with 2-mercaptobenzothiazole (MBT) was investigated as a new adsorbent for preconcentration of Cd(II), Cu(II) and Pb(II). The metal ions are adsorbed onto nano-TiO₂-MBT, eluted by nitric acid and determined by flame atomic absorption spectrometry. The parameters affecting the adsorption were investigated. Under optimized conditions, the calibration curves were linear in the range of 0.2–25.0, 0.2–20.0, and 3.0–70.0 ng mL⁻¹ for cadmium, copper and lead, respectively. The limits of detection for Cd(II), Cu(II) and Pb(II) were 0.12, 0.15 and 1.38 ng mL⁻¹, respectively. The method was applied to determination of Cd(II), Cu(II) and Pb(II) in water and ore samples.     

Selective solid-phase extraction of rare earth elements by the chemically modified Amberlite XAD-4 resin with azacrown ether

A selective solid-phase extraction procedure using chemically modified Amberlite XAD-4 with monoaza dibenzo 18-crown-6 ether was investigated for the preconcentration and separation of La(III), Nd(III) and Sm(III) in synthetic solution. Before loading samples on synthesized adsorbent adjust pH 4.5 by suitable buffer solution. The adsorbed rare earth elements were eluted by 2 M hydrochloric acid. Various parameters like preconcentration, breakthrough capacity, flow rate were investigated. The limits of detection (n = 5) and limits of quantification (n = 5) for La(III), Nd(III) and Sm(III) were founded 3.9, 4.2 and 7.4 μg L^?1 and 13, 15 and 26 μg L^?1, respectively. The eluted metal ions were determined by ICP-AES.     

Determination of gold and palladium in environmental samples by FAAS after dispersive liquid–liquid microextraction pretreatment

A new dispersive liquid–liquid microextraction (DLLME) method is proposed for rapid separation, simultaneous extraction and preconcentration of gold and palladium at ultra trace amounts. The extraction of the analytes was performed in the presence of 5-[(E)-(2,6-diaminopyridine-3-yl)diazenyl]-1,3,4-thiadiazole-2-thiol (DAT) as chelating agent. Chloroform and acetone were used as extraction and dispersive solvents, respectively. The variables affecting the complexation and extraction conditions were optimized. The calibration curves were linear in the range of 1.1–85 and 0.9–124 μg L⁻¹ with the detection limits of 0.4 and 0.6 μg L⁻¹, and with the enrichment factors of 94 and 113 for Au and Pd, respectively. The precision (RSD%) was better than 2.4%. The accuracy of the method was verified by analysing the certified standard reference material (CDN–PGMS-10). The results show that the dispersive liquid–liquid microextraction pretreatment is a sensitive, rapid, simple and safe method for the separation/preconcentration of gold and palladium.     

Imprinted polymer-based extraction for speciation analysis of inorganic tin in food and water samples

In this study, an ion imprinted polymer (IIP), tin (IV)–4-(2-pyridylazo) resorcinol (PAR) complex (Sn(IV)–PAR–IIP) has been synthesized for speciation and selective solid-phase extraction (SPE) of tin species from food and water samples. For this purpose, copolymerization of Sn(IV)–4-(2-pyridylazo) resorcinol (PAR) complex was performed using methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA), and 2,2′-Azobisisobutyronitrile (AIBN) as functional monomer, cross-linking agent, and initiator, respectively. The polymer particles were characterized by FT-IR, and thermogravimetric (TG) analyses. The effects of different variables such as solution pH, mass of the polymer, extraction and elution time, and type and volume of the eluent for elution of tin were evaluated by Box–Behnken design and response surface methodology. The significance of independent variables and their interactions were tested by the analysis of variance (ANOVA) with 95% confidence limits. The optimal conditions at extraction step were 8, 70 mg, and 25 min for solution pH, amount of polymer, and extraction time, respectively. Also, the optimal values for the elution step were 6.5 mL of HCl (4 M) as the eluent volume and type and elution time of 120 min. The detection limit of the proposed method was found to be 1.3 μg L^?1 and a linear dynamic range (LDR) in the range of 5–200 μg L^?1 was obtained. The influence of various cationic interferences on recovery percentage of Sn(IV) was studied. The method was applied to recovery and determination of tin species in different real samples.     

The use of a copper microelectrode to measure the ethanol content in gasohol samples

A method to quantify ethanol in gasohol fuels is described by using a copper microelectrode polarised at 0.6 V vs Ag/AgCl as an amperometric sensor. The determination was performed in a 1 mol L⁻¹ NaOH aqueous phase after extraction of ethanol from gasohol samples. The influence of the solution stirring on the ethanol extraction was investigated by monitoring the analyte with the sensor immersed in the aqueous phase. The electrochemical pre-treatment of the electrode surface has a great influence on the sensor response, the best sensitivity being achieved by polarising previously the electrode at −0.1 V vs Ag/AgCl. The repeatability of the amperometric method by measuring the ethanol content in a gasohol sample was found to be 3.4% (n = 10) and the limit of detection was 0.01% (v/v). Under the optimum experimental conditions, the amperometric sensor was used to monitor the concentration of ethanol in gasohol samples.     

Flame atomic absorption spectrometric determination of Cd,Pb, and Cu in food samples after pre-concentration using 4-(2-thiazolylazo) resorcinol-modified activated carbon

This work aimed to develop a solid-phase extraction method using low-cost activated carbon produced from waste and modified with 4-(2-thiazolylazo) resorcinol for Cd(II), Pb(II), and Cu(II). The results showed that quantitative recovery of analytes was obtained at pH 6 with 3 M nitric acid as the eluent and a sample volume up to 1000 mL. The method was validated using certified reference material and addition-recovery tests. The limits of detection (LODs) for Pb(II), Cd(II), and Cu(II) were 2.03 μg L⁻¹, 0.15 μg L⁻¹, and 0.19 μg L⁻¹, respectively. The procedure was applied for determination of analytes in food samples.     

Microfiltration of cationic dyes using nano-clay membranes

Water resources cover 70% of earth surface with only 3% as fresh and the remaining frozen or unavailable. As a result, water and wastewater treatment have attracted a great deal of attention during last decades. Among various pollutants, dyes in textile wastewaters can have serious impacts on the environment. In the present study, low-cost ceramic nano-clay microfiltration membranes with low sintering temperature were fabricated via dry pressing, with natural zeolite as pore former. Flat disks were fabricated by sintering a mixture with various proportions of clay, zeolite and polyethylene glycol at 900 °C and characterized using FE-SEM, open porosity test, zeta potential, water permeability and acid-base treatment. Also, Membrane porosity was enhanced by increasing the zeolite content reaching 30.2% at 30 wt% and then decreased. The 30% zeolite membrane was selected for microfiltration of methylene blue, crystal violet and methyl orange from aqueous solutions. Initial and time filtered solution concentrations for each dye were measured using a UV–visible spectrophotometer. Methylene blue and crystal violet are cationic dyes due to the presence of NC(CH)₃ ⁺ while SO₃^- makes methyl orange anionic. The membrane had negative charge at pH = 6, suggesting adsorption of cationic dyes as the removal mechanism. 95.55% removal of crystal violet was obtained for the 54 mg L⁻¹ solution at 1 bar and 90.23% removal of methylene blue was obtained at optimal conditions with a 35.76 mg L⁻¹ concentration and 1.5 bar transmembrane pressure. However, less than 10% methyl orange removal was obtained, due to its negative charge. Membranes can be recovered completely by eliminating the adsorbed dyes via heat treatment at 300 °C for 1 h. The results approve the as-fabricated clay membranes cost-effective with high rejection of cationic dyes.     

Acetylacetone phenylhydrazone functionalized polyurethane foam: Determination of copper,zinc and manganese in environmental samples and pharmaceutics using flame atomic absorption spectrometry

In the present work, acetylacetone phenylhydrazone (AAPH) was chemically anchored to polyurethane foam (PUF) via azo coupling of the toluidine NH₂ in PUF to active CH₂ in acetylacetone (AA) and further reaction to phenylhydrazine to give new solid phase extraction (SPE) sorbent for determination of Cu(II), Zn(II) and Mn(II) in natural and pharmaceutical samples. The AAPH–PUF was characterized by UV–VIS, IR, H¹ NMR, elemental and TGA analysis. Optimal experimental conditions were at pH 5–6, shaking time 20 min, sample flow rate 1.0 mL min^?1, and desorption by 10 mL from 0.5 mol L^?1 hydrochloric acid. The limit of detection (3σ) was found to be 0.10, 0.12 and 0.19 μg L^?1 for Cu(II), Zn(II) and Mn(II), respectively. A preconcentration factor of 100 has been achieved for all elements. Precision (RSD%) was found to be 6.3%, 5.3% and 3.2% (n = 5), respectively. Successful application was achieved for environmental samples (tap water, olive leaves, and fish liver) and pharmaceutical formulation. The obtained recovery varied between 90.8% and 96.8% and RSD was under 6.7%.