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.     

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).     

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.     

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.     

Separation and determination of cadmium in water by foam column prior to inductively coupled plasma optical emission spectrometry

The sorption profile of cadmium (II) ions from aqueous iodide media onto procaine hydrochloride (PQ⁺·Cl⁻) treated polyurethane foams (PUFs) solid sorbent was studied. PQ⁺·Cl⁻ treated PUFs solid sorbent was found suitable and fast for Cd²⁺ uptake as [CdI4]_aq²⁻. Thus, removal of Cd²⁺ at trace levels by the sorbent packed columns was achieved. The sorbed Cd²⁺ species onto packed column were recovered with HNO₃ (10.0 mL, 1.0 mol L⁻¹) prior determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). Plot of Cd²⁺ ions concentration was linear in the range 0.05–15 μg L⁻¹. The limits of detection and quantification of Cd²⁺ were found 0.01 μg L⁻¹ and 0.033 μg L⁻¹, respectively. Such limits could be improved to lower values by retention of Cd²⁺ species from large sample volumes of the aqueous phase at the optimized conditions. The relative standard deviation of the packed column for the extraction and recovery of standard aqueous solutions (0.1 L) containing 1.0 and 5.0 μg L⁻¹ (n = 3) of Cd²⁺ ions at flow rate of 5.0 mL min⁻¹ were 1.98 and 2.9%, respectively. The method was validated by analysis of Cd in certified reference materials (CRMs) IAEA-Soil-7 and TMDW water and wastewater samples.     

Anodic stripping voltammetry coupled with design of experiments for simultaneous determination of Zn+2, Cu+2, Pb+2, and Cd+2 in gasoline

In this paper a rapid method of anodic stripping voltammetry (ASV) coupled with experimental design was developed for simultaneous determination of Zn²⁺, Cd²⁺, Pb²⁺, and Cu²⁺ in gasoline samples. A microwave assisted gasoline digestion procedure for sample preparation was also established. The determination limit was found to be 0.24 μg L^?1 for Zn²⁺; 8.58 × 10^?4 μg L^?1 for Cd²⁺; 0.13 μg L^?1 for Pb²⁺, and 0.87 μg L^?1 for Cu²⁺. It was found that the interferences of concomitant metal ions were negligible. Gasoline samples collected in the city of São Luis (MA), Brazil were analyzed using this developed method, and the results demonstrated that this method was reliable and accurate. It is expected that this method can be used as a routine technique for metal ion determination in gasoline.     

Particulate carbon in precipitation at European background sites

The particulate carbon content of precipitation was investigated in samples collected at five background sites located over a west-east European transect, from the Azores, in the mid-Atlantic Ocean, to the Hungarian plain, in central Europe. Sampling was performed on an event basis and the particulate carbon (elemental carbon, EC, and water insoluble organic carbon, WIOC) content was concentrated on quartz filters for the subsequent analysis by a thermal optical method in order to separate the EC and WIOC fractions. The average EC concentrations range from low values at the Azores (2.8±4.3 μg C L^?1) and at the high mountain site of Sonnblick (5.2±3.7 μg C L^?1) to high values at the more inland sites of Schauinsland (28±38 μg C L^?1) and K-Puszta (24±24 μg C L^?1). The average WIOC concentrations range from 98±56 μg C L^?1 at the coastal site of Aveiro and 113±78 μg C L^?1 at the Azores to 358±194 μg C L^?1 at the continental site of K-Puszta. These results are discussed in terms of factors affecting the spatial distribution of particulate carbon, such as emissions from surrounding areas and prevalent meteorological conditions. EC is found to be a minor contributor to total particulate carbon present in rain and snow samples (from 2.5% to 15%). This is particularly true at the remotes sites, where the EC contribution to total particulate carbon is <6.5%, consistent with a negligible impact of anthropogenic combustions locally. The EC and WIOC scavenging ratios were estimated and compared with those of sulfate, also evaluated at the same sampling sites. The results indicated that EC is removed from the atmosphere by wet deposition less efficiently than WIOC, and in turn this species is removed less efficiently than sulfate.     

Effect of cellulosic sugar degradation products (furfural and hydroxymethyl furfural) on acetone–butanol–ethanol (ABE) fermentation using Clostridium beijerinckii P260

Studies were performed to identify chemical compounds present in wheat straw hydrolysate (WSH) that enhance acetone butanol ethanol (ABE) productivity. These compounds were identified as furfural and hydroxymethyl furfural (HMF). Control experiment resulted in the production of 21.38 g L^?1 ABE with a productivity of 0.30 g L^?1 h^?1. WSH contained 0.04–0.34 g L^?1 furfural and 0.12–0.88 g L^?1 HMF. Addition of furfural to the fermentation medium at a concentration of 0.50 g L^?1 resulted in a productivity of 0.88 g L^?1 h^?1 which is 293% of the productivity obtained in control experiments. Supplementation with 1.00 g L^?1 HMF into the fermentation medium produced 25.27 g L^?1 ABE with a productivity of 0.68 g L^?1 h^?1. A combination of furfural (0.50 g L^?1) and HMF (0.50 g L^?1) also enhanced ABE production and productivity when added to the fermentation medium. Both furfural and HMF enhanced specific productivity (233–308%) of ABE. In brief, WSH contained an adequate concentration of furfural and HMF that enhanced ABE productivity, specific productivity, and product concentration.     

Preparation of new heteronuclear (NH4)RE[FeII(CN)6]·nH2O complexes (RE = La,Ce, Pr,Nd, Sm,Gd, Dy,Y, Er,Lu) and their low-temperature decomposition for perovskite-type oxide

New heteronuclear (NH₄)RE^III[Fe^II(CN)₆]·nH₂O complexes (RE = La, Ce, Pr, Nd, Sm, Gd, Dy, Y, Er, Lu) were synthesized and their thermal decomposition products were investigated. The crystal structure of (NH₄)RE[Fe^II(CN)₆]·nH₂O would be a hexagonal unit cell (space group: P6₃/m), which was the same as that of La[Fe^III(CN)₆]·5H₂O. The hydration number n = 4 was estimated by TG results for all the RE complexes. The lattice constants depended on the ionic radius of the RE³⁺ ion for the heteronuclear complexes. The single phase of the perovskite type materials was directly obtained by decomposition of the heteronuclear complexes for RE = La, Pr, Nd, Sm, and Gd. A mixture of CeO₂ and Fe₂O₃ was formed for RE = Ce because of its oxidation to Ce⁴⁺. In the case of RE = Dy, Y, Er, and Lu complexes, the perovskite type materials formed at higher temperature via. mixed oxides such as RE₂O₃ and RE₄Fe₅O₁₃ due to the small RE³⁺ ionic radius.     

Application of PSO-artificial neural network and response surface methodology for removal of methylene blue using silver nanoparticles from water samples

In this study, a simple and fast method for preconcentration and determination of trace amount of methylene blue (MB) from water samples was developed by silver nanoparticles based solid-phase extraction method and UV–Vis spectrophotometry. Response surface methodology and hybrid of artificial neural network- particle swarm optimization (ANN-PSO) have 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 15.0 μg L^?1 and <2.7%, respectively. The preconcentration factor was 83. The method was applied to preconcentration and determination of methylene blue from water 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.     

Synthesis,characterisation and cryomagnetic studies of a novel homonuclear Nd(III) Schiff base dimer

A novel homodinuclear complex [Nd^III(L)(NO₃)]₂ (1) has been synthesised [H₂L = N¹,N³- bis(salicylideneimino)diethylenetriamine, a pentadentate Schiff base with N₃O₂ donor set] and characterised with spectroscopic and micro-analytical techniques. Single crystal X-ray diffraction study reveals a centrosymmetric binuclear neutral entity [space group, P2₁/n; a = 12.911(5); b = 11.938(5); c = 13.960(5) Å; Z = 4] where Nd(III) metal centers are bridged together by two phenoxo oxygen atoms each coming from the two ligands. The most interesting fact is that two similar “salen” moieties of each ligand are behaving completely different in their coordination. In the doubly deprotonated ligand (L²⁻), one phenoxo oxygen is mono coordinated to the metal, whereas its immediate neighbour on the other end bridges the two Nd(III) centers. The distance between the Nd(III) centers is found to be 3.884(3) Å. Temperature dependence (2–300 K) magnetic susceptibility study suggests the presence of an antiferromagnetic interaction operating via two phenoxo bridges.     

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.     

Flow injection analysis of free glycerol in biodiesel using a copper electrode as an amperometric detector

The main goal of this work was to develop a simple analytical method for quantification of glycerol based on the electrocatalytic oxidation of glycerol on the copper surface adapted in a flow injection system. Under optimal experimental conditions, the peak current response increases linearly with glycerol concentration over the range 60–3200 mg kg^?1 (equivalent to 3–160 mg L^?1 in solution). The repeatability of the electrode response in the flow injection analysis (FIA) configuration was evaluated as 5% (n = 10), and the detection limit of the method was estimated to be 5 mg kg^?1 in biodiesel (equivalent to 250 μg L^?1 in solution) (S/N = 3). The sample throughput under optimised conditions was estimated to be 90 h^?1. Different types of biodiesel samples (B100), as in the types of vegetable oils or animal fats used to produce the fuels, were analysed (seven samples). The only sample pre-treatment used was an extraction of glycerol from the biodiesel sample containing a ratio of 5 mL of water to 250 mg of biodiesel. The proposed method improves the analytical parameters obtained by other electroanalytical methods for quantification of glycerol in biodiesel samples, and its accuracy was evaluated using a spike-and-recovery assay, where all the biodiesel samples used obtained admissible values according to the Association of Official Analytical Chemists.     

Non-volatile vanadium determination in petroleum condensate,diesel and gasoline prepared as detergent emulsions using GF AAS

The development of a procedure for non-volatile vanadium determination in petroleum derivative products by graphite furnace atomic absorption spectrometry (GF AAS) using sample preparation as detergent emulsion is presented. Emulsions of samples were make using concentrate nitric acid, Triton X-100, samples and water in the proportions of 1/1/2/6 respectively. Doehlert design was applied as experimental matrix to optimize the temperature program. A comparative study among the slopes of some analytical curves built in aqueous, surfactant and organic media and by analyte addition in several sample emulsions (diesel, gasoline and condensate) shows that a unique solution of surfactant in acid media can be used to make the calibration solutions. The developed procedure allows the determination of non-volatile vanadium in these samples with limit of detection (LOD) and limit of quantification (LOQ) of 14 and 45 μg L^?1, respectively. Precision, expressed as relative standard deviation (% RSD, n = 10) for 20 and 80 μg L^?1 were 6.4–2.9%, respectively. The proposed procedure was applied in the determination of vanadium in samples of petroleum condensate, gasoline and diesel. Accuracy was evaluated by spike tests in the analyzed samples. Results of recovery between 90% and 105% show that it can be successfully applied to this kind of 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%.     

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.     

Pre-concentration and determination of traces of nitrobenzene and 1,3-dinitrobenzene in water samples using anthracite adsorbent

This study introduces a novel analytical method for the determination of nitrobenzene (NB) and 1,3-dinitrobenzene (DNB) from an aqueous solution using high performance liquid chromatography (HPLC) and anthracite as adsorbent for pre-concentration. The method showed good linearity for determination of NB and DNB concentrations in the range of 0.10–200 μg L⁻¹ with regression coefficients better than 0.9995. Limits of detections (LOD) were 0.010 and 0.055 μg L⁻¹ for DNB and NB, respectively. Relative standard deviations (RSD) for 0.50 μg L⁻¹ and 150 μg L⁻¹ were in the range of 2.0–3.8% for (DNB) and 3.0–4.8% for (NB).     

Characterization of catalysts in their active state by adsorption microcalorimetry: Experimental design and application to sulfated zirconia

A method to characterize the surface sites of catalysts in their active state by adsorption microcalorimetry was developed. A calorimeter cell was used as a flow-type reactor, and the skeletal isomerization of n-butane (1 kPa) at 378 K and atmospheric pressure proceeded at comparable rates and with the same states of induction period, maximum and deactivation phase as in a tubular reactor. The reaction was run for selected times on stream and after the removal of weakly adsorbed species, n-butane or isobutane were adsorbed at 313 K. The surface of activated sulfated zirconia was characterized by at least two different sites for n-butane adsorption, a small group of sites (about 20 μmol g^?1) that yielded heats of 50–60 kJ mol^?1 and sites that were populated at higher pressures (above about 5 hPa n-butane) and yielded heats of about 40 kJ mol^?1. The strongly interacting sites disappear during the induction period and are proposed to be the sites where the isomerization reaction is initiated.