Detection of nitrification inhibitor dicyandiamide: A direct electrochemical approach.

A single run approach for rapid detection of nitrification inhibitor, dicyandiamide (DCD) using electrogenerated chlorine assisted polymerization through azo bond, under acidic conditions and at a preanodized screen printed carbon electrode (SPCE*) is presented. The role of chloride containing support electrolyte in acidic medium along with oxygen functionalities/edge sites are found to be crucial for the successful oxidative polymerization and subsequent adsorption of oxidized products on the electrode surface. The SEM, cyclic voltammetry and X-ray photoelectron spectroscopy studies were used to characterize the polymer film formation. The system exhibited a linear range between 20 and 170 µM with a detection limit of 3 µM (S/N = 3). The method was successfully tested for the detection of DCD in dairy and water samples. Simultaneous detection of DCD in the presence of melamine has also been demonstrated.

Electrografting of 4-Carboxybenzenediazonium on Glassy Carbon Electrode: The Effect of Concentration on the Formation of Mono and Multilayers.

Grafting of electrodes with diazonium salts using cyclic voltammetry (CV) is a well-established procedure for surface modification. However, little is known about the effect of the concentration of the diazonium salt on the number of layers grafted on the electrode surface. In this work, the impact of concentration on the grafting of 4-carboxybenzenediazonium (4-CBD) onto a glassy carbon electrode (GCE) is elucidated. The number of layers grafted on the GCE was linearly dependent on the concentration of 4-CBD and varied between 0.9 and 4.3 when the concentration was varied between 0.050 and 0.30 mmol/L at 0.10 V.s-1. Characterization of modified glassy carbon surface with X-ray photoelectron spectroscopy (XPS) confirmed the grafting of carboxyphenyl layer on the surface. Grafting with 0.15 mmol/L 4-CBD (1 CV cycle) did not form a detectable amount of carboxyphenyl (CP) moieties at the surface, while a single scan with higher concentration (2.5 mmol/L) or multiple scans (22 cycles) gave detectable signals, indicating formation of multilayers. We also demonstrate the possibility of removing the thin layer grafted on a glassy carbon electrode by applying high oxidation potential +1.40 V.

Experimental and Theoretical Study of the Covalent Grafting of Triazole Layer onto the Gold Surface.

Finding novel strategies for surface modification is of great interest in electrochemistry and material sciences. In this study, we present a strategy for modification of a gold electrode through covalent attachment of triazole (TA) groups. Triazole groups were electrochemically grafted at the surface of the electrode by a reduction of in situ generated triazolediazonium cations. The resulting grafted surface was characterized before and after the functionalization process by different electrochemical methods (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS)) confirming the presence of the grafted layer. The grafting of TA on the electrode surface was confirmed using analysis of surface morphology (by atomic force microscopy), the thickness of the grafted layer (by ellipsometry) and its composition (by X-ray photoelectron spectroscopy). Density functional theory (DFT) calculations imply that the grafted triazole offers a stronger platform than the grafted aryl layers.

Interaction of anions with lipid cubic phase membranes, an electrochemical impedance study.

HYPOTHESIS: Electrochemical impedance spectroscopy is useful to monitor anionic interactions with a Lipid Cubic Phase, as previously demonstrated for cationic interaction (Khani Meynaq et al., 2016). It was expected that the smaller hydrophilic anions, acetate and chloride, would interact differently than the large tryptophan anion with its hydrophobic tail. EXPERIMENT: The impedance measurements enabled estimation of resistances and capacitances of a freestanding lipid cubic phase membrane at exposure to 4 and 40 mM solutions of NaCl, NaOAc and NaTrp. Small-angle X-ray scattering was used for cubic phase identification and to track structural changes within the cubic phase when exposed to the different electrolytes. FINDINGS: The membrane resistance increases at exposure to the electrolytes in the order Cl- < OAc- < Trp-. The membrane resistance decreases with time at exposure to the hydrophilic anions and increases with time at Trp- exposure. The membrane capacitances were lower for NaTrp compared to NaCl and NaOAc at the corresponding concentrations which is consistent with the results from SAXRD. It is concluded that Trp- ions do not enter the aqueous channels of the cubic phase but are strongly adsorbed to the membrane/electrolyte interface leading to large alteration of the lipid phase structure and a high membrane resistance.

Cationic interaction with phosphatidylcholine in a lipid cubic phase studied with electrochemical impedance spectroscopy and small angle X-ray scattering.

HYPOTHESIS: Electrochemical Impedance Spectroscopy (EIS) can be used to investigate cationic interaction with the choline headgroup in the ternary system of monoolein/dioleoylphosphatidylcholine/water (MO/DOPC/H2O). EXPERIMENTS: EIS was used to estimate the resistance and capacitance of a freestanding membrane of a lipid cubic phase (LCP). The membrane was formed in a small cylindrical aperture separating two compartments, containing one Pt electrode each. The impedance experiments were carried out in a two electrode setup with electrolyte solutions made of KCl, CsCl, MgCl2 and CaCl2 filling the compartments at two different ionic strength. Small angle X-ray diffraction (SAXRD) was used to establish the structure and cell unit parameters of the LCP. FINDINGS: The interpretation of ionic interaction with phosphatidylcholine was based on estimated membrane resistances and capacitances from EIS measurements. The magnitude of cationic interaction with the lipid headgroup in the water channels is correlated to the membrane resistance that increases in the order Cs+ < K+ < Mg2+ < Ca2+ following the Hofmeister direct series and also reflecting the order of intrinsic binding constants. The membrane capacitance and SAXRD results are discussed as an effect of cationic interaction and it was possible to observe both swelling and condensing effects. The stability of the cubic phase throughout the experiments was confirmed by SAXRD.

Determination of methotrexate in spiked human blood serum using multi-frequency electrochemical immittance spectroscopy and multivariate data analysis.

This article describes an attempt to develop a sensor based on multi-frequency immittance spectroscopy for the determination of methotrexate (MTX) in blood serum using gold electrodes modified with antibodies. The attachment of antibodies was monitored with electrochemical immittance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The EIS measurements of MTX resulted in a data matrix of size 39 × 55. The data were analysed using multivariate data analysis and showed a concentration dependence and time dependence that could be separated. This allowed the calculation of a multivariate calibration model. The model showed good linear behavior on a logarithmic scale offering a detection limit of 5 × 10-12 mol L-1.

Investigation of metal ion interaction with a lipid cubic phase using electrochemical impedance spectroscopy.

HYPOTHESIS: Electrochemical impedance spectroscopy, EIS, can be used as a complementary technique to investigate ion interaction with the headgroup region in the aqueous channels of a lipid cubic phase, LCP. EXPERIMENTS: A freestanding membrane made of monoolein LCP was formed by filling a small aperture that separates two cell compartments. The cell compartments were filled with electrolyte solutions at two different ionic strengths: i.e.: 10 and 100mM, of KCl, CsBr and CaCl2. Electrochemical impedance spectroscopy was recorded between two platinum electrodes that were present at each side of the membrane. FINDINGS: The membrane resistance and capacitance were estimated from equivalent circuit fitting of the impedance data. It was confirmed that calcium ions interacts strongly with the headgroup region in the aqueous channels giving significantly higher membrane resistances compared to monovalent alkali metal ions. The membrane capacitance with Ca(2+)(aq) in solution was concentration dependent, which for the first time indicates formation of two different cubic phases at these conditions.

Detection of methotrexate in a flow system using electrochemical impedance spectroscopy and multivariate data analysis.

Methotrexate (MTX), a common pharmaceutical drug in cancer therapy and treatment of rheumatic diseases, is known to cause severe adverse side effects at high dose. As the side effect may be life threatening, there is an urgent need for a continuous, bed-side monitoring of the nominal MTX serum level in a patient while the chemical is being administered. This article describes a detection of MTX using a flow system that consists two modified gold electrodes. Interaction of MTX with the antibodies fixed on the electrode surface is detected by electrochemical impedance spectroscopy and evaluated using singular value decomposition (SVD). The key finding of this work is that the change in the electrode capacitance is found to be quantitative with respect to the concentration of MTX. Moreover a calibration curve constructed using the principal component regression method has a linear range of six orders of magnitude and a detection limit of 1.65 × 10(-10) M.

Towards universal wavelength-specific photodegradation rate constants for methyl mercury in humic waters, exemplified by a Boreal lake-wetland gradient.

We report experimentally determined first-order rate constants of MeHg photolysis in three waters along a Boreal lake-wetland gradient covering a range of pH (3.8-6.6), concentrations of total organic carbon (TOC 17.5-81 mg L(-1)), total Fe (0.8-2.1 mg L(-1)), specific UV254 nm absorption (3.3-4.2 L mg(-1) m(-1)) and TOC/TON ratios (24-67 g g(-1)). Rate constants determined as a function of incident sunlight (measured as cumulative photon flux of photosynthetically active radiation, PAR) decreased in the order dystrophic lake > dystrophic lake/wetland > riparian wetland. After correction for light attenuation by dissolved natural organic matter (DOM), wavelength-specific (PAR: 400-700 nm, UVA: 320-400 nm and UVB: 280-320 nm) first-order photodegradation rate constants (kpd) determined at the three sites were indistinguishable, with average values (± SE) of 0.0023 ± 0.0002, 0.10 ± 0.024 and 7.2 ± 1.3 m(2) E(-1) for kpdPAR, kpdUVA, and kpdUVB, respectively. The relative ratio of kpdPAR, kpdUVA, and kpdUVB was 1:43:3100. Experiments conducted at varying MeHg/TOC ratios confirm previous suggestions that complex formation with organic thiol groups enhances the rate of MeHg photodegradation, as compared to when O and N functional groups are involved in the speciation of MeHg. We suggest that if the photon fluxes of PAR, UVA, and UVB radiation are separately determined and the wavelength-specific light attenuation is corrected for, the first-order rate constants kpdPAR, kpdUVA, and kpdUVB will be universal to waters in which DOM (possibly in concert with Fe) controls the formation of ROS, and the chemical speciation of MeHg is controlled by the complexation with DOM associated thiols.

Determination of melamine in milk powder using zwitterionic HILIC stationary phase with UV detection.

A hydrophilic interaction liquid chromatography-UV method was developed for the determination of melamine in milk powder. Sulfobetaine type zwitterionic hydrophilic interaction liquid chromatography stationary phase was used to achieve straightforward separation of melamine in milk powder without any sample derivatization or addition of ion-pair reagent. The sample preparation was simple and fast with the steps of acetonitrile/perchloric acid extraction-centrifugation-filtration. No SPE or other pre-concentration procedure was required. By using large volume sample injection and choosing low UV wavelength (210 nm), the LOD and LOQ were 0.005 and 0.015 microg/mL for melamine standards, and 0.02 and 0.06 microg/mL for the spiked milk extracts. The LOD and LOQ of the latter correspond to 0.95 and 2.2 microg/g melamine in the milk powder. The correlation coefficients for melamine standard, pre-spiked milk extracts and post-spiked milk extracts in the range of 0-0.5 microg/mL were 0.9978, 0.9976 and 0.9995, respectively. This newly developed method is sensitive and cost effective, therefore, suitable for screening of melamine in tainted milk products.

Arsenic chemical species-dependent genotoxic potential in water extracts from two CCA-contaminated soils measured by DNA-repair deficient CHO-cells.

Two soils with similar contamination levels from wood preservatives containing Chromium (Cr), Copper (Cu) and Arsenic (As) (CCA), were assessed for their general toxicity and genotoxicity. A set of water-based extraction methods, including pressurized liquid extraction (PLE), and batch leaching in milli-Q water and a weak CaCl(2)-solution, was used to produce soil extracts containing available fractions of contaminants. In addition, to obtain indications of the contaminants' bioavailability and toxic potential the genotoxicity of the extracts was estimated by testing their ability to inhibit the growth of wildtype Chinese hamster ovary cells (CHO-cells) and three genetically modified phenotypes that are deficient in different DNA-repair mechanisms. Total extractable arsenic concentrations in the extracts were comparable between the sites. However, the genotoxic potential was clearly higher in soil R extracts. The differences in genotoxic responses were related to differences in inorganic arsenic speciation. The ratio of trivalent arsenic (As(III)) to pentavalent arsenic (As(V)) was higher in all soil extracts from soil R, regardless of the leaching method used. The results of the various combinations of soil extraction techniques and assays using the CHO-cell lines reflected important differences in arsenic speciation in the two soils and possible synergistic effects in CCA-related exposure. They also indicate that speciation and combinatory effects are factors that should be taken into account when assessing risks at former wood impregnation sites contaminated by CCA-agents.

Impact of water saturation level on arsenic and metal mobility in the Fe-amended soil.

The impact of water saturation level (oxidizing-reducing environment) on As and metal solubility in chromium, copper, arsenic (CCA)-contaminated soil amended with Fe-containing materials was studied. The soil was mixed with 0.1 and 1 wt% of iron grit (Fe(0)) and 1, 7 and 15 wt% of oxygen scarfing granulate (OSG, a by-product of steel processing). Solubility of As and metals was evaluated by a batch leaching test and analysis of soil pore water. Soil saturation with water greatly increased As solubility in the untreated as well as in the Fe-amended soil. This was related to the reductive dissolution of Fe oxides and increased concentration of As(III) species. Fe amendments showed As reducing capacity under both oxic and anoxic conditions. The cytotoxicity of the soil pore water correlated with the concentration of As(III). The Fe-treatments as well as water saturation of soil were less significant for the solubility of Cu, Cr and Zn than for As. The batch leaching test used for waste characterization substantially underestimated As solubility that could occur under water-saturated (anaerobic) conditions. In the case of soil landfilling, other techniques than Fe-stabilization of As containing soil should be considered.

The transformation of phenyltin species during sample preparation of biological tissues using multi-isotope spike SSID-GC-ICPMS.

A multi-isotope spike species-specific isotope dilution (MI-SSID) calibration strategy in connection with gas chromatography-inductively coupled plasma mass spectrometry was applied to evaluate different extraction procedures for the speciation analysis of phenyltin (PhT) compounds in biological materials: mussel tissue BCR CRM-477 and fish tissue NIES-11. Three different isotope-enriched PhT compounds, (118)Sn-enriched monophenyltin (MPhT), (122)Sn-enriched diphenyltin (DPhT), and (124)Sn-enriched triphenyltin (TPhT), were used for the preparation of spikes to follow and correct for six possible interconversion reactions between PhT species that can take place in a sample. The acidity of the extractant, the presence of complexing reagents, and the use of ultrasonic or microwave agitation were found to affect the degradation of PhT compounds. No formation of PhTs through phenylation and negligible degradation of MPhT to inorganic tin were observed under the conditions investigated. The degree of degradation increased with increased acidity of extractant and when ultrasonication or microwave agitation was used. Under relatively mild extraction conditions, the degradation factors for DPhT and TPhT in the two reference materials studied were found, using MI-SSID, to be between 10 and 55% and 2 and 10%, respectively. Using the degradation factors, we calculated corrected concentration values for the organotin species. When microwave extraction at high power output was used, hydrogen radicals were formed that can enhance the degradation of DPhT and TPhT. The hydrogen radicals were trapped using N-tert-butyl-alpha-phenylnitrone and detected by electron spin resonance spectrometry. The effect of different extraction parameters on the degradation of PhT compounds in biological samples is discussed.

Techniques for the stabilization and assessment of treated copper-, chromium-, and arsenic-contaminated soil.

Remediation mainly based on excavation and burial of the contaminated soil is impractical with regard to the large numbers of sites identified as being in need of remediation. Therefore, alternative methods are needed for brownfield remediation. This study was conducted to assess a chemical stabilization procedure of CCA-contaminated soil using iron (Fe)-containing blaster sand (BS) or oxygen-scarfing granulate (OSG). The stabilization technique was assessed with regard to the feasibility of mixing ameliorants at an industrial scale and the efficiency of the stabilization under different redox conditions. The stability was investigated under natural conditions in 1-m3 lysimeters in a field experiment, and the effect of redox conditions was assessed in a laboratory experiment (10 L). The treatments with high additions of ameliorant (8% and 17%) were more successful in both the laboratory and field experiments, even though there was enough Fe on a stochiometric basis even at the lowest addition rates (0.1% and 1%). The particle size of the Fe and the mixing influenced the stabilization efficiency. The development of anaerobic conditions, simulated by water saturation, increases the fraction of arsenic (AsIII) and, consequently, As mobility. The use of high concentrations of OSG under aerobic conditions increased the concentrations of nickel (Ni) and copper (Cu) in the pore water. However, under anaerobic conditions, it decreased the As leaching compared with the untreated soil, and Ni and Cu leaching was not critical. The final destination of the treated soil should govern the amendment choice, that is, an OSG concentration of approximately 10% may be suitable if the soil is to be landfilled under anaerobic conditions. Alternatively, the soil mixed with 1% BS could be kept under aerobic conditions in a landfill cover or in situ at a brownfield site. In addition, the treatment with BS appeared to produce better effects in the long term than treatment with OSG.

Field trials to assess the use of iron-bearing industrial by-products for stabilisation of chromated copper arsenate-contaminated soil.

Two industrial by-products with high iron contents were tested for their effectiveness in the stabilisation of arsenic and trace metals in chromated copper arsenate (CCA)-contaminated soil. Steel abrasive (SA; 97% Fe(0)) and oxygen scarfing granulate (OSG; 69% Fe(3)O(4)) were applied at levels of 1% and 8% (w/w) respectively to two soils with different organic matter contents. Field lysimeter measurements indicated that SA and OSG treatments decreased the arsenic concentration in pore water by 68% and 92%, respectively, for the soil with low organic matter content, and by about 30% in pore water of soil with high organic matter content. At pH < or =6, the amended soil with low organic content contained elevated levels of manganese and nickel in their pore water, which were sufficient to induce cytotoxic effects in L-929 mouse fibroblast cells. The industrial by-products have significant potential for soil amendment at field-scale, but caution is required because of the potential release of their chemical contaminants and their reduced capacity for sorption of arsenic in organic-rich soils.

Preparation, preservation and application of pure isotope-enriched phenyltin species.

A method combining liquid/liquid extraction and chromatographic fractionation has been developed for the preparation of pure monophenyltin (MPhT), diphenyltin (DPhT), and triphenyltin (TPhT), synthesized from isotope-enriched Sn metal using phenylation of SnI(4) in diethylether (DEE) followed by quenching with HBr and water. After two successive extractions of the aqueous HBr phase with DEE, >99% of both DPhT and TPhT was recovered in the combined DEE phase and 94% of the MPhT remained in the aqueous phase. The MPhT in the aqueous phase was extracted into dichloromethane. The organic phases were vaporized and the PhTs were redissolved in MeOH/water/acetic acid/sodium acetate (59/30/6/8, v/v/v/w), which was also used as storing solution. Aliquots of the two solutions containing either DPhT and TPhT or MPhT were injected into a silica-based C(18) column for isolating and purifying single species. The yields of pure MPhT, DPhT, and TPhT, each synthesized from isotope-enriched (118)Sn metal, (122)Sn metal, and (124)Sn metal, were better than 99%. After chromatographic separation, the single phenyltin compounds were mixed to prepare a spike for multiple-isotope species-specific isotope dilution (MI-SSID). MI-SSID was successfully used to determine phenyltin compounds in the certified reference material, mussel tissue BCR CRM-477. At -20 degrees C, all of the fractionated phenyltin species were stable in the storage solution for at least 197 days. When these standards were stored at 4 degrees C or 22 degrees C, 4-6% of the DPhT and TPhT degraded within 27 days. The degradation of DPhT and TPhT increased with the ionic strength and acidity of the storage solution.