LC-MS analysis of nitroguanidine compounds by catalytic reduction using palladium modified graphitic carbon nitride catalyst.

The analysis of compounds of the nitroguanidine family at trace level poses an analytical challenge. Nitroguanidine, 1-methyl-3-nitroguanidine, and 1-methyl-3-nitro-1-nitrosoguanidine, which are addressed in this article, have low lipophilicity, with log(Kow) equal to -0.89, - 0.84, and 0.68, respectively, and as such are not amenable for preconcentration from water. Liquid-liquid extraction and SPE fail to concentrate them from water and it is also not possible to extract them by ion exchange resin even after a pH change. Nitroguanidine and 1-methyl-3-nitroguanidine nitramines are explosives of growing use and thereby growing environmental concern due to lower detonation sensitivity compared to RDX. A sensitive method for the determination of nitroguanidine, 1-methyl-3-nitroguanidine, and 1-methyl-3-nitroso-1-nitroguanidine by reduction to the respective amines and subsequent hydrophobization by derivatization with 4-nitrobenzaldehyde followed by LC-ESI-MS analysis is described. Reduction by sodium borohydride using palladium modified graphitic carbon nitride (Pd/g-C3N4) provided improved sensitivity compared to the traditional palladium modified activated carbon due to the lower adsorption of the reduction products on the carbon nitride substrate. The limit of detection of the method was 10 ng L-1 for nitroguanidine, and repeated analyses of spiked effluents and contaminated spring water gave relative standard deviations of 8.8% and 6.5%, respectively. The findings illuminate the great promise of Pd/g-C3N4 as a reduction catalyst for the determination of challenging hydrophilic organic contaminants.

Emerging pollutant mixture mineralization by TiO2 photocatalysts. The role of the water medium.

Pharmaceutics and personal care products (PPCPs) are raising growing concern due to their widespread usage and resistance to conventional remediation techniques. Several of them raise significant health and environmental concerns, especially when present in complex mixtures. Due to their chemical resistance, Advanced Oxidation Processes (AOPs) are needed for their complete removal from surface and wastewaters. In the present work, photocatalysis by titanium dioxide (TiO2) under UV and simulated solar irradiation was adopted to degrade tetracycline hydrochloride, paracetamol, caffeine and atenolol, both as single pollutants and in mixtures. All molecules showed high removal and mineralization degrees. Moreover, no interference effects decreased the efficiency of the processes in the case of pollutant mixtures, achieving 60% of mineralization after 6 h. An immobilized TiO2 system was also developed by depositing titania on titanium meshes. A 50% mineralization degree of the pollutant mixture was obtained after 6 h, revealing a suitable efficiency for field applications. Eventually, the impact of the matrix composition on the photocatalytic efficiency was investigated by studying the reaction both in simulated drinking water and in commercial bottled mineral water. The scavenger role played by HCO3- species appears to be dominant in inhibiting the mineralization.

Synthesis of Water Dispersible and Catalytically Active Gold-Decorated Cobalt Ferrite Nanoparticles.

Hetero-nanoparticles represent an important family of composite nanomaterials that in the past years are attracting ever-growing interest. Here, we report a new strategy for the synthesis of water dispersible cobalt ferrite nanoparticles (CoxFe3-xO4 NPs) decorated with ultrasmall (2-3 nm) gold nanoparticles (Au NPs). The synthetic procedure is based on the use of 2,3-meso-dimercaptosuccinic acid (DMSA), which plays a double role. First, it transfers cobalt ferrite NPs from the organic phase to aqueous media. Second, the DMSA reductive power promotes the in situ nucleation of gold NPs in proximity of the magnetic NP surface. Following this procedure, we achieved a water dispersible nanosystem (CoxFe3-xO4-DMSA-Au NPs) which combines the cobalt ferrite magnetic properties with the catalytic features of ultrasmall Au NPs. We showed that CoxFe3-xO4-DMSA-Au NPs act as an efficient nanocatalyst to reduce 4-nitrophenol to 4-aminophenol and that they can be magnetically recovered and recycled. It is noteworthy that such nanosystem is more catalytically active than Au NPs with equal size. Finally, a complete structural and chemical characterization of the hetero-NPs is provided.

Photo-renewable electroanalytical sensor for neurotransmitters detection in body fluid mimics.

A composite electrode with a sandwich structure combining the properties of silver nanoparticles and a titania photoactive layer was used for the electroanalytical detection, by differential pulse voltammetry, of three neurotransmitters: dopamine, norepinephrine, and serotonin. The three analytes were determined at low detection limits (around 0.03 µM) also in the presence of conventional interferents, such as uric and ascorbic acids. The fouling of the electrode surface was overcome by irradiating the device with UVA light, restoring the initial sensor sensitivity. Dopamine, norepinephrine, and serotonin were determined also in simulated biological matrices: liquor (artificially reproduced cerebrospinal fluid) and serum. Moreover, the contemporaneous detection of dopamine and norepinephrine in simulated human urine solutions was also demonstrated, representing the first step towards clinical applications of the proposed methodology. Graphical abstract The photo-renewable electroanalytical sensor.

Au-Based Catalysts: Electrochemical Characterization for Structural Insights.

Au-based catalysts are widely used in important processes because of their peculiar characteristics. The catalyst performance depends strongly on the nature and structure of the metal nanoparticles, especially in the case of bimetallic catalysts where synergistic effects between the two metals can be occasionally seen. In this paper, it is shown that electrochemical characterisation (cyclovoltammetry CV and electrochemical impedance spectroscopy EIS) of AuPd systems can be used to determine the presence of an electronic interaction between the two metals, thus providing a strong support in the determination of the nature of the synergy between Au and Pd in the liquid phase oxidation of alcohols. However, it seems likely that the strong difference in the catalytic behavior between the single metals and the bimetallic system is connected not only to the redox behaviour, but also to the energetic balance between the different elementary steps of the reaction.

Self-cleaning properties in engineered sensors for dopamine electroanalytical detection.

Fouling and passivation are the major drawbacks for a wide applicability of electroanalytical sensors based on nanomaterials, especially in biomedical and environmental fields. The production of highly engineered devices, designed ad hoc for specific applications, is the key factor in the direction of overcoming the problem and accessing effective sensors. Here, the fine-tuning of the system, composed of a highly ordered distribution of silver nanoparticles between a bottom silica and a top titania layer, confers multifunctional properties to the device for a biomedical complex challenge: dopamine detection. The crucial importance of each component towards a robust and efficient electroanalytical system is studied. The total recovery of the electrode performance after a simple UV-A cleaning step (self-cleaning), due to the photoactive interface and the aging resistance, is deeply investigated.

Enlightening the bimetallic effect of Au@Pd nanoparticles on Ni oxide nanostructures with enhanced catalytic activity.

Bimetallic decoration of semiconductor electrodes typically improves catalytic and sensing performances because of a well-claimed synergistic effect. A microscopic and quantitative investigation of such an effect on energy bands of semiconductor can be really useful for further exploitation. Au, Pd and Au@Pd (core@shell) nanoparticles (10-20 nm in size) were synthesized through chemical reduction method and characterized with scanning and transmission microscopy, Rutherford backscattering spectrometry, cyclic voltammetry electrochemical impedance spectroscopy and Mott-Schottky analysis. The nanoparticles have been used to decorate Ni-based nanostructured electrodes with the aim to quantitatively investigate the effect of decoration with mono or bimetallic nanoparticles. Decorated electrodes show higher redox currents than bare ones and a shift in redox peaks (up to 0.3 V), which can be ascribed to a more efficient electron transport and improved catalytic properties. These effects were satisfactorily modeled (COMSOL) employing a nano Schottky junction at the nanoparticle-semiconductor interface, pointing out large energy band bending (up to 0.4 eV), space charge region and local electric field (up to [Formula: see text]) in bimetallic decoration. Sensing test of glucose and H2O2 by decorated Ni oxide electrodes were performed to consolidate our model. The presence of bimetallic nanoparticles enhances enormously the electrochemical performances of the material in terms of sensitivity, catalytic activity, and electrical transport. The modification of energy band diagram in semiconductor is analyzed and discussed also in terms of electron transfer during redox reactions.

Nanosponges by the oxo-Michael polyaddition of cyclodextrins as sorbents of water pollutants: the o-toluidine case.

Hydrophilic cyclodextrin nanosponges were prepared by the oxo-Michael polyaddition in an aqueous solution at pH > 10 of α-, ß-, and γ-cyclodextrin with 1,4-bisacryloylpiperazine or 2,2-bisacrylamidoacetic acid. These nanosponges and, for comparison purposes, their precursor cyclodextrins were tested as sorbents of o-toluidine, a carcinogenic wastewater contaminant, by monitoring the depletion of o-toluidine from a 10-4 M (10 ppm) aqueous solutions. To this aim, an innovative analytical procedure was used: The voltammetric peak currents of o-toluidine in linear sweep voltammetry experiments were registered using multi-walled carbon nanotubes-modified glassy carbon electrodes. The experimental sorption curves fitted a mono-exponential kinetic model, and the residual o-toluidine was 0.16 ppm, one order of magnitude lower than those of all other sorbents reported so far. The sorption capacities ranged from 88 to 199 µmol g-1 (10-21.3 mg g-1), equal to or higher than those of the parent cyclodextrins. All nanosponges were completely regenerated by extracting with methanol. After regeneration, the sorption capacity slightly improved, suggesting a rearrangement of the nanosponge network. Overall, it may be reasonably concluded that the cyclodextrin nanosponges reported in this paper warrant potential as o-toluidine exhaustive sorbents.

Gold nanoparticles modified graphene platforms for highly sensitive electrochemical detection of vitamin C in infant food and formulae.

An easy and reliable method based on a novel electroanalytical nanostructured sensor has been developed to perform quantification of vitamin C in commercial and fortified cow-milk-based formulae and foods for infants and young children. The work is motivated by the need of a reliable analytical tool to be applied in quality control laboratories for the quantitative assessment of vitamin C where its rapid and cost-effective monitoring is essential. The ad hoc designed sensor, based on disposable screen-printed carbon electrodes modified with Au nanoparticles decorated reduced graphene oxide flakes, exhibits a LOD of 0.088 mg L-1. The low cost, easy sample preparation, fast response and high reproducibility (RSD ≈ 8%) of the proposed method highlight its suitability for usage in quality control laboratories for determining vitamin C in real complex food matrices, envisaging the application of the sensing platform in the determination of other compounds relevant in food chemistry and food manufacturing.

Towards molecular design rationalization in branched multi-thiophene semiconductors: the 2-thienyl-persubstituted alpha-oligothiophenes.

The introduction of branching in multi-thiophene semiconductors, although granting the required solubility for processing, results in an increased molecular fluxionality and a higher level of distortion, thus hampering pi conjugation. Accordingly, branched oligothiophenes require rationalization of their structure-reactivity relationships for target-oriented design and optimization of the synthetic effort. Our current research on spiderlike oligothiophenes affords deep insight into the subject, and introduces new, easily accessible molecules with attractive functional properties. In particular, a regular series, T'X(Y), of five new multi-thiophene systems, T'5(3), T'8(4), T'11(5), T'14(6), and T'17(7), constituted by five, eight, 11, 14, and 17 thiophene units, respectively, their longest alpha-conjugated chain consisting of tri-, tetra-, penta-, hexa-, and heptathiophene moieties, respectively, has been synthesized and fully characterized from the structural, spectroscopic, and electrochemical point of view. The electronic properties of the monomers and their electropolymerization ability are discussed and rationalized as a function of their molecular structure, particularly in comparison with the series of 5-(2,2'-dithiophene)yl-persubstituted alpha-oligothiophenes (TX(Y)) previously reported by us. These oligothiophenes are easily accessible materials, with promising properties for applications as active layers in multifunctional organic devices including solar cells.

Efficiency of an Air Cleaner Device in Reducing Aerosol Particulate Matter (PM) in Indoor Environments.

Indoor air quality (IAQ) in household environments is mandatory since people spend most of their time in indoor environments. In order to guarantee a healthy environment, air purification devices are often employed. In the present work, a commercial household vacuum cleaner has been tested in order to verify its efficiency in reducing the mass concentration and particle number of aerosol particulate matter (PM). The efficiency has been tested measuring, while the instrument was working, PM10 (particles with aerodynamic diameter less than 10 µm), PM2.5 (particles with aerodynamic diameter less than 2.5 µm), PM1 (particles with aerodynamic diameter less than 1 µm), and 7 size-fractions in the range between 0.3 and >10 µm. Measurements have been carried out by means of a portable optical particle counter instrument and simulating the working conditions typical of a household environment. It has been found that the tested commercial device significantly reduces both PM concentrations and particle number, especially in the finest fraction, i.e., particles in the range 0.3-0.5 µm, allowing an improvement of indoor air quality.

Chlorine Dioxide Degradation Issues on Metal and Plastic Water Pipes Tested in Parallel in a Semi-Closed System.

Chlorine dioxide (ClO2) has been widely used as a disinfectant in drinking water in the past but its effects on water pipes have not been investigated deeply, mainly due to the difficult experimental set-up required to simulate real-life water pipe conditions. In the present paper, four different kinds of water pipes, two based on plastics, namely random polypropylene (PPR) and polyethylene of raised temperature (PERT/aluminum multilayer), and two made of metals, i.e., copper and galvanized steel, were put in a semi-closed system where ClO2 was dosed continuously. The semi-closed system allowed for the simulation of real ClO2 concentrations in common water distribution systems and to simulate the presence of pipes made with different materials from the source of water to the tap. Results show that ClO2 has a deep effect on all the materials tested (plastics and metals) and that severe damage occurs due to its strong oxidizing power in terms of surface chemical modification of metals and progressive cracking of plastics. These phenomena could in turn become an issue for the health and safety of drinking water due to progressive leakage of degraded products in the water.

A Combined XRD, Solvatochromic, and Cyclic Voltammetric Study of Poly (3,4-Ethylenedioxythiophene) Doped with Sulfonated Polyarylethersulfones: Towards New Conducting Polymers.

Despite the poor solubility in organic solvents, poly (3,4-ethylenedioxythiophene) (PEDOT) is one of the most successful conducting polymers. To improve PEDOT conductivity, the dopants commonly used are molecules/polymers carrying sulfonic functionalities. In addition to these species, sulfonated polyarylethersulfone (SPAES), obtained via homogeneous synthesis with different degrees of sulfonation (DS), can be used thanks to both the tight control over the DS and the charge separation present in SPAES structure. Here, PEDOTs having enhanced solubility in the chosen reaction solvents (N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone) were synthesized via a high-concentration solvent-based emulsion polymerization with very low amounts of SPAES as dopant (1% w/w with respect to EDOT monomer), characterized by different DS. The influence of solvents and of the adopted doping agent was studied on PEDOT_SPAESs analyzing (i) the chemical structure, comparing via X-ray diffraction (XRD) the crystalline structures of undoped and commercial PEDOTs with PEDOT_SPAES' amorphous structure; (ii) solvatochromic behavior, observing UV absorption wavelength variation as solvents and SPAES' DS change; and (iii) electrochemical properties: voltammetric peak heights of PEDOT_SPAES cast onto glassy carbon electrodes differ for each solvent and in general are better than the ones obtained for neat SPAES, PEDOTs, and glassy carbon.

Atomistic Explanation for Interlayer Charge Transfer in Metal-Semiconductor Nanocomposites: The Case of Silver and Anatase.

A concerted theoretical and experimental investigation of the silver/anatase hybrid nanocomposite, a very promising material for advanced sensing applications, is presented. We measure its exceptional electrochemical virtues in terms of current densities and reproducibility, providing their explanation at the atomic-scale level and demonstrating how and why silver acts as a positive electrode. Using periodic plane-wave DFT calculations, we estimate the overall amount of electron transfer toward the semiconductor side of the interface at equilibrium. Suitably designed (photo)electrochemical experiments strictly agree, both qualitatively and quantitatively, with the theoretical charge transfer estimates. The unique permanent charge separation occurring in the device is possible because of the favorable synergy of Ag and TiO2, which exploits in a favorable band alignment, while the electron-hole recombination rate and carrier mobility decrease when electrons cross the metal-semiconductor interface. Finally, the hybrid material is proven to be extremely robust against aging, showing complete regeneration, even after 1 year.

A Nanostructured Matrices Assessment to Study Drug Distribution in Solid Tumor Tissues by Mass Spectrometry Imaging.

The imaging of drugs inside tissues is pivotal in oncology to assess whether a drug reaches all cells in an adequate enough concentration to eradicate the tumor. Matrix-Assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI-MSI) is one of the most promising imaging techniques that enables the simultaneous visualization of multiple compounds inside tissues. The choice of a suitable matrix constitutes a critical aspect during the development of a MALDI-MSI protocol since the matrix ionization efficiency changes depending on the analyte structure and its physico-chemical properties. The objective of this study is the improvement of the MALDI-MSI technique in the field of pharmacology; developing specifically designed nanostructured surfaces that allow the imaging of different drugs with high sensitivity and reproducibility. Among several nanomaterials, we tested the behavior of gold and titanium nanoparticles, and halloysites and carbon nanotubes as possible matrices. All nanomaterials were firstly screened by co-spotting them with drugs on a MALDI plate, evaluating the drug signal intensity and the signal-to-noise ratio. The best performing matrices were tested on control tumor slices, and were spotted with drugs to check the ion suppression effect of the biological matrix. Finally; the best nanomaterials were employed in a preliminary drug distribution study inside tumors from treated mice.

Relevance of electron transfer mechanism in electrocatalysis: the reduction of organic halides at silver electrodes.

The mechanism of dissociative electron transfer (ET) to a series of organic chlorides has been investigated both at an inert electrode and at a catalytic surface such as Ag; electrocatalysis is important only when breaking of the carbon-halogen bond is concerted with the ET.

New CNT/poly(brilliant green) and CNT/poly(3,4-ethylenedioxythiophene) based electrochemical enzyme biosensors.

A combination of the electroactive polymer poly(brilliant green) (PBG) or conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) with carbon nanotubes to obtain CNT/PBG and CNT/PEDOT modified carbon film electrodes (CFE) has been investigated as a new biosensor platform, incorporating the enzymes glucose oxidase (GOx) as test enzyme, alcohol oxidase (AlcOx) or alcohol dehydrogenase (AlcDH). The sensing parameters were optimized for all biosensors based on CNT/PBG/CFE, CNT/PEDOT/CFE platforms. Under optimized conditions, both GOx biosensors exhibited very similar sensitivities, while in the case of AlcOx and AlcDH biosensors, AlcOx/CNT/PBG/CFE was found to give a higher sensitivity and lower detection limit. The influence of dissolved O2 on oxidase-biosensor performance was investigated and was shown to be different for each enzyme. Comparisons were made with similar reported biosensors, showing the advantages of the new biosensors, and excellent selectivity against potential interferents was successfully demonstrated. Finally, alcohol biosensors were successfully used for the determination of ethanol in alcoholic beverages.

rH-metric controls and primary standardization in aqueous-organic media.

The rationale for the extension of the rH-metric standardization and measurements to aqueous-organic solvent mixtures is here introduced, and examples of establishment of the ranges of conventional rH-metric scales as well as primary standards rHs in some typical aqueous-organic solvent mixtures are described.

Problems in assessments of amalgam electrodes for standardising or certifying the corresponding ion selective electrodes.

The primary method for standardizing or certifying an Mz+-ISE (Ion Selective Electrode for Mz+ where Mz+ = alkali or alkaline-earth cation) implies comparing the latter with the corresponding M-Amalgam electrode in the cell Pt/M-Amalgam/Mz+ Solution/Mz+ ISE/Pt, whose potential difference is obviously independent of Mz+ concentration. Assessment of the potential of the M-Amalgam electrode requires the precise determination of the mole fraction x of the M metal in amalgam, which is customarily performed by decomposing an M-Amalgam sample in excess HCl and titrating the HCl excess with standard NaOH solution. There arises the problem of choosing the correct end-point in pH-metric titrations of strong acids with carbonate-contaminated NaOH standard solutions, which is of frequent occurrence both in research and routine laboratory practice. This topic is either overlooked or insufficiently treated in textbooks: thus the interpretation of the above experimental pH-metric titration curves is often misled and the results may be affected by significant errors. Some recent misleading suggestions are here re-analyzed critically in order to focus correct, recommended methodological schemes.

Salivary glucose concentration and daily variation in the oral fluid of healthy patients.

AIM: The aim of this study was to determine the concentration and the variations of salivary glucose in healthy patients who were sampled at five different intervals during the day. MATERIALS AND METHODS: Samples of un-stimulated saliva have been collected from 21 healthy patients using the drooling technique and they were divided into two categories. In the first category, patients were asked not to toothbrush their teeth in the 8 hours prior to collection of the salivary sample. Patients in the second category were instead asked to toothbrush 90 minutes before the collection of the first sample of saliva. The glucose concentration was measured in all patients via an enzymatic spectrophotometry. Patients have been selected following a strict inclusion criteria, which included <5% of plaque presence e according to the plaque Index and a total absence of oral disease that could possibly interfere with sample taking or oral fluid analysis. The average age of patients was 22,4±2,6 years old of which 45% were female and 55% were male. Samples were collected five times between 8 am and 12 pm, before and after breakfast. Data was statistically analyzed using the Skewness/Kurtosis Test, Shapiro-Wilk Test, Kruskal Wallis Test and Linear Regression Model, considering values of p<0,05 to be significant. RESULTS: The average rate of un-stimulated salivary flow was 0,53±0,21 ml/min. There were no significant differences between salivary glucose values and salivary flow in female and male patients. However, we observed a typical trend which recurred for each patient and resembled a "pseudo-glycemic curve". CONCLUSIONS: The collected data suggests that glucose concentration results did not show statistically significant differences (p>0,078) which could however be due to the little number of patients assessed, nonetheless there is a trend, recalling a "pseudo-glycemic curve" not referable to changes in flow rates, probably due to glucose catabolism and shunt.