Self-assembled monolayer modified gold electrodes for traces Cu(II) determination

d,l-Penicillamine and thiodimethylglyoxime (TDMG) self-assembled monolayers (SAMs) on gold electrode were prepared and characterized by electrochemical measurements. The two sensors exhibit sensitive and selective response to Cu(II), both forming 2:1 complexes, the first one in acetic buffer and the second one in ammonia buffer. Copper determination at trace level (LOQ 0.2 and 0.3 microg/L for d,l-penicillamine and TDMG, respectively) is possible with both the electrodes as verified in tap, spring and sea water. The influence on copper determination of most common ions present in natural waters and of organic matter has been investigated. Accuracy was checked by recovery test on spiked samples

Solid-phase extraction of PFOA and PFOS from surface waters on functionalized multi-walled carbon nanotubes followed by UPLC-ESI-MS

This is the first report on the analytical application of multiwalled carbon nanotubes (MWCNTs) as solid-phase extraction (SPE) sorbents for determination in surface waters, at the nanograms per litre level, of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), the two predominant contaminants among the perfluorinated compounds detected. After the preconcentration step, the quantification was achieved by ultraperformance liquid chromatography– electrospray ionization mass spectrometry. To increase the extraction efficiency towards these amphiphilic compounds, MWCNTs were derivatized with amino-terminated alkyl chains, thus producing a mixed-mode material (MWCNT-RNH2) combining hydrophobic affinity and anion-exchange properties. Experiments with distilled, tap and river water (pH 3) spiked at different concentrations (10, 15, 30, 100, 200 and 500 ng L-1) provided absolute recoveries in the range 71–102 % (n=3, relative standard deviations less than 10 %). Analytes were eluted in a single fraction with 6 mL methanol (3×10-4 M NaOH). The within-laboratory reproducibility of the MWCNT-R-NH2 SPE sorbent was evaluated with raw river water, and relative standard deviations less than 15 % were obtained (n=4). Preconcentration factors up to 125 (500-mL sample) made it possible to quantify PFOA and PFOS at low nanograms per litre levels in naturally contaminated river water. The method quantification limits of 10 ng L-1 for PFOA and 15 ng L-1 for PFOS were well below the advisory levels for drinking and surface waters. Comparison with non-derivatized MWCNTs highlighted the role of functionalization in improving the adsorption affinity towards these contaminants. MWCNT-R-NH2 maintained their extraction capability for at least eight repeated adsorption/desorption cycles

HPLC-MS/MS multiclass determination of steroid hormones in environmental waters after preconcentration on the carbonaceous sorbent HA-C@silica

In this study, a sensitive and multiclass method has been developed for analysis of three families of steroid hormones, i.e. progestins, oestrogens, androgens, by SPE-HPLC-ESI-MS/MS. The extraction efficiency of thermally condensed humic acids onto silica sorbent (HA-C@silica), here for the first time studied for multiclass enrichment of these sex hormones, was tested in different environmental waters (tap and river water, urban wastewater treatment plant effluent) spiked at the nanograms per litre levels (5–1000 ng L−1). Quantitative adsorption was achieved using 200 mg sorbent for preconcentration of 250–1000 mL sample, at the native pH (pH = 6.5–7.7). Elution was performed by two sequential fractions (methanol followed by acetonitrile), obtaining in all the matrices investigated satisfactory recoveries (71% to 124% for river waters and 71–113% for urban wastewater treatment plant effluent) and RSDs below 15% (n = 3). The high enrichment factors (up to 4000) coupled with high-performance liquid chromatography tandem mass spectrometry quantification (MRM mode) provided low limits of detection and quantification (a few ng L−1), that are suitable for environmental monitoring. Most of the analytes were detected in river water and in wastewater effluent samples (in the ng L−1 concentration range), attesting their environmental diffusion. The proposed method was extended to a fourth class, Glucocorticoids, achieving good results in river samples, by the same SPE cartridge and chromatographic run. Keywords: Environmental waters, Steroid hormones, Multiclass determination, HPLC-MS, Pollutants, Solid-phase extractio

speciation of copper ii in natural waters in the presence of ligands of high and intermediate strength

AbstractA new procedure is presented for the determination of the ligands of copper(II) in natural waters, based on titration with the metal ion, monitored by measuring the concentration of copper(II) sorbed on the carboxylic resin Amberlite CG 50. The data are treated by the Ruzic linearization method to obtain the concentration of the ligands and the conditional stability constant of the complexes. Ligands with reaction coefficient αM higher than 0.1 K*w/V are detected, where K* is the ratio of the concentration of sorbed metal to the concentration of free metal in solution, which can be evaluated from the sorption equilibria of copper(II) on Amberlite CG 50, w is the amount of water in the resin phase, and V the volume of the solution phase. Some natural waters at high and low salinity were examined. The ligand concentration determined in these samples ranged from around 50 to 2000 nM, while the original copper concentrations from 11 to 130 nM. The ligand concentration was always much higher than that ..

Intermolecular interactions of substituted benzenes on multi-walled carbon nanotubes grafted on HPLC silica microspheres and interaction study through artificial neural networks

Purified multi-walled carbon nanotubes (MWCNTs) grafted onto silica microspheres by gamma-radiation were applied as a HPLC stationary phase for investigating the intermolecular interactions between MWCNTs and substituted benzenes. The synthetic route, simple and not requiring CNTs derivatization, involved no alteration of the nanotube original morphology and physical–chemical properties. The affinity of a set of substituted benzenes for the MWCNTs was studied by correlating the capacity factor (k′) of each probe to its physico-chemical characteristics (calculated by Density Functional Theory). The correlation was found through a theoretical approach based on feedforward neural networks. This strategy was adopted because today these calculations are easily affordable for small molecules (like the analytes), and many critical parameters needed are not known. This might increase the applicability of the proposed method to other cases of study. Moreover, it was seen that the normal linear fit does not provide a good model. The interaction on the MWCNT phase was compared to that of an octadecyl (C18) reversed phase, under the same elution conditions. Results from trained neural networks indicated that the main role in the interactions between the analytes and the stationary phases is due to dipole moment, polarizability and LUMO energy. As expected for the C18 stationary phase correlation, is due to dipole moment and polarizability, while for the MWCNT stationary phase primarily to LUMO energy followed by polarizability, evidence for a specific interaction between MWCNTs and analytes. The CNT-based hybrid material proved to be not only a chromatographic phase but also a useful tool to investigate the MWCNT-molecular interactions with variously substituted benzenes. Keywords: Carbon nanotubes, Feedforward neural networks, Intermolecular interaction, Liquid chromatograph

Tuning retention and selectivity in reversed-phase liquid chromatography by using functionalized multi-walled carbon nanotubes

Aim of this work was to explore the possibility of retention and selectivity tuning in reversed-phase liquid chromatography by means of chemically modified multi-walled carbon nanotubes (MWCNTs). These were synthesized by derivatizing pristine MWCNTs with amino-terminated alkyl chains containing polar embedded groups. A novel hybrid material based on functionalized MWCNTs (MWCNTs-R-NH2) was prepared, characterized and tested. The idea was to design a mixed-mode separation medium basing its sorption properties on the peculiar characteristics of MWCNTs combined with the chemical interactions provided by the functional chains introduced on the nanotube skeleton. MWCNTs-R-NH2 were easily grafted to silica microspheres by gamma radiation (using a 60Co source) in the presence of polybutadiene as the linking agent. The composite was characterized by scanning electron microscopy (SEM) and Brunauer, Emmett and Teller (BET) analysis in terms of structural morphology, surface area and porosity. The MWCNTs-R-NH2 sorbent was tested as stationary phase. The reversed-phase behaviour was first proved by analysis of alkylbenzenes, while the key role of CNT derivatization in addressing the selectivity/affinity towards the solutes was evidenced by testing three classes of analytes, viz. barbiturates, steroid hormones and alkaloids. These compounds, with different molecular structure and polarity, were here analysed for the first time on CNT-based LC stationary phases. The behaviour of the novel sorbent was compared in terms of retention capability and resolution with that observed using unmodified MWCNTs, pointing out the mixed-mode characteristics of the MWCNTs-R-NH2 material. The same test mixtures were analysed also on a conventional mono-modal separation sorbent (C18) to highlight the particular behaviour of the (derivatized)MWCNTs-based stationary phases. The novel material showed better performance in separation of polar compounds, i.e. barbiturates and alkaloids, than the unmodified MWCNTs and than the C18 column. Results showed that MWCNT functionalization is powerful to modulate retention/selectivity in reversed-phase liquid chromatography. Keywords: Functionalized carbon nanotubes, Liquid chromatography, Mixed-mode stationary phase

Application of the new electroanalytical technique AGNES for the determination of free Zn concentration in river water

Absence of gradients and Nernstian equilibrium stripping (AGNES) is a recently developed electroanalytical technique specifically designed for the direct determination of free concentrations of metal ions. AGNES is applied here to the determination of free Zn concentration in a river water sample. The method has been validated with synthetic solutions of low ionic strengths containing Zn and 2,6-pyridinedicarboxylic acid and then applied to synthetic river waters and to a natural sample collected from Besòs River in Montcada i Reixac (Catalonia, North-Eastern Spain). In the river sample, an average free Zn concentration of 12.8(4) nM was obtained, while the total dissolved Zn concentration was 0.51(8) μM. To control and maintain pH and pCO2 constant during AGNES measurements, a novel device for N2/CO2 mixed purging has been developed

Solid-phase extraction of vanadium(V) from teainfusions and wines on immobilized nanometer titanium dioxide followed by ICP-OES analysis

Nanosized titanium dioxide immobilized on silica gel was synthesized and used as fixedbed phase for V(V) pre-concentration, followed by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. Three different sorbents were prepared by sol\u2013gel method starting from a mixture of titanium isopropoxide, 2-propanol and water, and characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and BET analysis. V(V), the most stable and toxic oxidation state of the element, present in water and beverages samples, was selectively sorbed, pre-concentrated, quantitatively eluted by 0.1 M HCl and analyzed by ICP-OES. The effectiveness of the procedure was first assessed on tap water enriched with 1 lg L1 of V(V) obtaining recoveries up to 92% (n= 4). The pre-concentration step was then optimized for complex matrices such as tea infusions and red and white wines. The reliability of the procedure was assessed on the same beverages samples spiked with 20\u2013250 lg L1. Quantitative recoveries (82\u2013 95%, n= 4) were assured avoiding any sample pre-treatment, generally essential in such complex matrices, obtaining good precision (RSD< 12%, n= 3). The method was then applied to the determination of V(V) in commercial tea infusions and wines

Combined Layer-by-Layer/Hydrothermal Synthesis of Fe3O4@MIL-100(Fe) for Ofloxacin Adsorption from Environmental Waters

: A simple not solvent and time consuming Fe3O4@MIL-100(Fe), synthesized in the presence of a small amount of magnetite (Fe3O4) nanoparticles (27.3 wt%), is here presented and discussed. Layer-by-layer alone (20 shell), and combined layer-by-layer (5 shell)/reflux or /hydrothermal synthetic procedures were compared. The last approach (Fe3O4@MIL-100_H sample) is suitable (i) to obtain rounded-shaped nanoparticles (200-400 nm diameter) of magnetite core and MIL-100(Fe) shell; (ii) to reduce the solvent and time consumption (the layer-by-layer procedure is applied only 5 times); (iii) to give the highest MIL-100(Fe) amount in the composite (72.7 vs. 18.5 wt% in the layer-by-layer alone); (iv) to obtain a high surface area of 3546 m2 g-1. The MIL-100(Fe) sample was also synthesized and both materials were tested for the absorption of Ofloxacin antibiotic (OFL). Langmuir model well describes OFL adsorption on Fe3O4@MIL-100_H, indicating an even higher adsorption capacity (218 ± 7 mg g-1) with respect to MIL-100 (123 ± 5 mg g-1). Chemisorption regulates the kinetic process on both the composite materials. Fe3O4@MIL-100_H performance was then verified for OFL removal at µg per liter in tap and river waters, and compared with MIL-100. Its relevant and higher adsorption efficiency and the magnetic behavior make it an excellent candidate for environmental depollution