Determination of parathion in the presence of paraoxon and p-nitrophenol by flow-injection analysis with amperometric detection

The amperometric determination of parathion in the presence of its metabolites paraoxon and p-nitrophenol in a flow-injection system is reported. The method is based on the measurement of the oxidation signal yielded by p-nitrophenol on hydrolysis of parathion in the presence of Pd(II) or Hg(II). The oxidation of the metabolite was preferred to its reduction as it avoids the removal of oxygen, which poses major problems in flow-through configurations.     

Ultrasensitive electrochemical sensor for p-nitrophenyl organophosphates based on ordered mesoporous carbons at low potential without deoxygenization

p-Nitrophenyl organophosphates (OPs) including paraoxon, parathion and methyl parathion, etc, are highly poisonous OPs, for which sensitive and rapid detection method is most needed. In this work, an ultrasensitive electrochemical sensor for the determination of p-nitrophenyl OPs was developed based on ordered mesoporous carbons (OMCs) modified glassy carbon electrode (GCE) (OMCs/GCE). The electrochemical behavior and reaction mechanism of p-nitrophenyl OPs at OMCs/GCE was elaborated by taking paraoxon as an example. Experimental conditions such as buffer pH, preconcentration potential and time were optimized. By using differential pulse voltammetry, the current response of the sensor at −0.085 V was linear with concentration within 0.01–1.00 μM and 1.00–20 μM paraoxon. Similar linear ranges of 0.015–0.5 μM and 0.5–10 μM were found for parathion, and 0.01–0.5 μM and 0.5–10 μM for methyl parathion. The low limits of detection were evaluated to be 1.9 nM for paraoxon, 3.4 nM for parathion and 2.1 nM for methyl parathion (S/N = 3). Common interfering species had no interference to the detection of p-nitrophenyl OPs. The sensor can be applicable to real samples measurement. Therefore, a simple, sensitive, reproducible and cost-effective electrochemical sensor was proposed for the fast direct determination of trace p-nitrophenyl OPs at low potential without deoxygenization.     

Encapsulation of bacteria in silica gels

Escherichia coli cells have been encapsulated within sol-gel silica matrices. The cellular organization of these bacteria appears to be well preserved. Their β-galactosidase activity was measured via the hydrolysis of p-NPG. The formation of p-nitrophenol was followed by optical absorption. These experiments show that the enzymatic activity of entrapped cells still exhibit a Michaelis behaviour. Their affinity toward the p-NPG substrate seems even better when the cells are trapped. They can be kept for days in wet gels but their activity decreases drastically upon drying.     

Synthesis of porous vinylnaphthalene/divinylnaphthalene copolymers and their sorptive properties towards phenol and its derivatives

Four porous vinylnaphthalene/divinylnaphthalene (VN/DVN) polymers having three different nominal crosslinking degrees (60, 80 and 100 wt.%) have been synthesized using the suspension polymerization method in the presence of toluene and decane.The use of various crosslinking levels and inert diluents was aimed at changing the extent of polymeric network-diluent interactions. The resultant polymers have specific surface area in the range 450-700 m²/g depending on the DVN content. Two sets of pores were detected in all resins: one with the diameter of ≈2 nm and the second one in the range of 30-40 nm. Their sorptive properties have been studied using dilute (0.5 mmol/l) solutions of phenol and its derivatives (o-chlorophenol, 2-methylphenol, o-nitrophenol, m-nitrophenol and p-nitrophenol). It has been found that sorption, at low equilibrium concentration, follows the order: o-nitrophenol > o-chlorophenol > m-nitrophenol > o-methylphenol > p-nitrophenol > phenol. Full characteristics of the porous structure of resultant polymers was obtained by nitrogen adsorption at 77 K and their surface properties analyzed using Inverse Gas Chromatography.     

Amides as a model system of low molar mass algal organic matter. Influence on the adsorption of p-nitrophenol on activated carbon

In this study, the adsorption equilibrium and diffusivity parameters of p-nitrophenol were estimated for water containing different concentrations of secondary amides. Commercial powdered activated carbon was used as an adsorbent. The external mass transfer coefficient (k_f), the surface diffusion coefficient (D_s) and the standard free Gibbs energy were calculated for p-nitrophenol in the presence of different secondary amide concentrations. The analysis established that there are correlations between structural parameters of amides, on the one hand, and diffusion and thermodynamic parameters for p-nitrophenol adsorption process, on the other. It was noticed that voluminous hydrophobic amides decreased the adsorption capacity of p-nitrophenol on activated carbon. On the basis of the results obtained for external mass transfer coefficients, it is assumed that amides cause the reduction of adsorption capacity of p-nitrophenol onto activated carbon by concentrating at the solid/liquid interface.     

Pyrolysis—high-resolution mass spectrometry of biological materials

In a diseased state in man or animals a change at eh molecular level might occur. A pyrolysis-high-resolution mass spectrometric method has been developed to measure these changes. The mass spectra are used as fingerprints. A similar approach is reported using low-resolution mass spectrometry. The difference between low resolution and high resolution is that the number of mass spectral lines is strongly increased and therefore also the information content. As a result, a change at the molecular level will be more pronounced in high-resolution mass spectra. As an application, the results of toxicity studies on Daphnia magna are given. The experiments were performed with paraoxon, parathion and malathion. The changes at the molecular level in Daphnia magna appear to be substance-dependent.     

Spectroscopic studies on the proton transfer and hydrogen bonding interactions between p-nitrophenol and aliphatic tertiary amines

The interaction of p-nitrophenol with aliphatic tertiary amines, namely triethylamine, tributyl-amine and trioctylamine, has been examined in a variety of solvents by means of electronic absorption spectroscopy. The acid—base interaction in these systems leads to various types of complexes depending upon the dielectric constant of the medium. The equilibrium data for different kinds of equilibria have been evaluated and discussed. The pK-equilibrium constant plots are found to be linear.     

A microconductometric biosensor based on lipase extracted from Candida rugosa for direct and rapid detection of organophosphate pesticides

Organophosphate pesticides (OPs) have been intensively used as insecticides in agriculture; after entering the aquatic environment, they may affect a wide range of organisms. A conductometric enzymatic biosensor based on lipase extracted from Candida rugosa (CRL) has therefore been developed for the direct and rapid quantitative detection of organophosphate pesticides: diazinon, methyl parathion and methyl paraoxon in water. The biosensor signal and response time were obtained under optimum conditions, the enzyme being immobilised in the presence of gold nanoparticles. Under these conditions, the enzymatic biosensor was able to measure concentrations as low as 60 µg/L of diazinon, 26 µg/L of methyl parathion and 25 µg/L of methyl paraoxon very rapidly (response time: 3 min). Moreover, this CRL biosensor was not sensitive to interferences such as carbamates. It presented good storage stability for 21 days when kept at 4°C and it was successfully applied to real samples.     

Adsorption of p-nitrophenol on organoclays

In this study, organoclays were prepared through ion exchange of a single cationic surfactant, hexadecyltrimethylammonium bromide and characterised by a range of methods including X-ray diffraction (XRD) and thermogravimetric analysis. Changes in the surface properties of montmorillonite and the organoclays were observed and the basal spacings of organoclays with and without p-nitrophenol were determined using XRD. The thermal stability of both organoclays were measured using thermogravimetry. As the surfactant loading increased, the expanded basal spacings were observed, and different molecular configurations of surfactant were identified. When the surfactant loading exceeded 1.0 CEC, surfactant molecules tend to adsorb strongly on the clay surface and this resulted in increased affinity to organic compounds. The adsorbed p-nitrophenol and the surfactant decomposed simultaneously. Hence, the surfactant molecules and adsorbed p-nitrophenol are important in determining the thermal stabilities of organoclays. This study enhances the understanding of the structure and adsorption properties of organoclays and has further implications for the application of organoclays as filter materials for the removal of organic pollutants in aqueous solutions.     

Degradation of the insecticide parathion in methanol by gamma-irradiation

The gamma-radiation from⁶⁰Co was used to induce parathion degradation in methanol solution, and the resulting products were quantified by GC-NPD and identified by GC-MS. The insecticide was completely degraded (99%) in methanol after treatment with 30 kGy doses at a dose rate of 3.12 kGy h⁻¹. The metabolites detected after radiolysis were p-aminophenol, paraoxon and aminoparathion, but no p-nitrophenol. The parathion radiation yield (G-parathion) in methanol solution was also calculated.     

Partial molar volumes of organic solutes in water. VIII. Nitrobenzene and nitrophenols at T=298 K to T=573 K and pressures up to 30 MPa

Density data for dilute aqueous solutions of nitrobenzene and three isomeric nitrophenols (2-, 3-, or 4-nitro-1-hydroxybenzene) are presented together with partial molar volumes at infinite dilution calculated from the experimental data. The measurements were performed at T=298.15 K up to either T=573.15 K (nitrobenzene, m-nitrophenol) or T=548.15 K (p-nitrophenol) or T=523.15 K (o-nitrophenol) and at either atmospheric pressure, or at pressures close to the saturated vapor pressure of water, and also at p=30 MPa. The data were obtained using a high-temperature high-pressure flow vibrating-tube densimeter for measurements at elevated pressures and a commercial vibrating-tube cell DMA 602HT for measurements at atmospheric pressure.     

Comparison of stir bar sorptive extraction and membrane-assisted solvent extraction as enrichment techniques for the determination of pesticide and benzo[a]pyrene residues in Brazilian sugarcane juice

The biodegradation of the organophosphorus insecticide methyl parathion (MP) in aqueous environment by bacteria isolated from river sediment has been studied. Two species of bacteria which show strong MP degradation ability are identified as Shewanella and Vibrio parahaemolyticus. The biodegradation of MP proceeded rapidly with the formation of a series of intermediate products, which were analyzed using a combination of GC/MS and HPLC/ESI-TOFMS techniques. The major products tentatively identified include a series of reduced products of MP. Results demonstrate that the coupling of TOFMS to HPLC enhances further the capability of LC-MS in the identification of polar organic species in complex environmental samples. Degradation pathways leading to the formation of these products are proposed which involves first the reduction of nitro to amino group in MP, followed by combination with some intrinsic matters of bacteria. The mechanism and products from biodegradation are quite different from those of photocatalytic process for which the main intermediates included methyl paraoxon and 4-nitrophenol.     

Micellar‐accelerated hydrolysis of organophosphate and thiophosphates by pyridine oximate

Rate constants for the hydrolysis reaction of phosphate (paraoxon) and thiophosphate (parathion, fenitrothion) esters by oximate (pyridinealdoxime 2‐PyOx⁻ and 4‐PyOx⁻) and its functionalized pyridinium surfactants 4‐(hydroxyimino) methyl)‐1‐alkylpyridinium bromide ions (alkyl = C_nH_2n+1, n = 10, 12, 14, 16) have been measured kinetically at pH 9.5 and 27°C in micellar media of cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB). Acid dissociation constant, pK_a, of oximes has also been determined by spectrophotometric, kinetic, and potentiometric methods. The rate acceleration effects of cationic micelles have been explored. Cationic micelles of the pyridinium head group (CPB) showed a large catalytic effect than the ammonium head group (CTAB). The effects of pH, oximate concentration, and surfactants have been discussed.     

Liquid–Liquid Microextraction of Nitrophenols Using Supramolecular Solvent and Their Determination by HPLC with UV Detection

A novel, efficient, and environmentally friendly method—supramolecular solvent liquid–liquid microextraction (SMS-LLME) combined with high-performance liquid chromatography (HPLC)—was first established for the determination of p-nitrophenol and o-nitrophenol in water samples. Several important parameters influencing extraction efficiency, such as the type and volume of extraction solvent, pH of sample, temperature, salt effect, extraction time, and stirring rate, were optimized in detail. Under the optimal conditions, the enrichment factor was 166 for p-nitrophenol and 160 for o-nitrophenol, and the limits of detection by HPLC were 0.26 and 0.58 μg L^?1, respectively. Excellent linearity with coefficients of correlation from 0.9996 to 0.9997 was observed in the concentration range of 2–1,000 μg L^?1. The ranges of intra- and interday precision (n = 5) at 100 μg L^?1 of nitrophenols were 5.85–7.76 and 10.2–11.9 %, respectively. The SMS-LLME method was successfully applied for preconcentration of nitrophenols in environmental water samples.     

Biosynthesis of Gold Nanoparticles by Flavonoids from <Emphasis Type="Italic">Lilium casa blanca</Emphasis>

Biosynthesis of gold nanoparticles (GNPs) by flavonoids from Lilium casa blanca has been developed. Several parameters such as pH, reaction temperature, reaction time and concentration of flavonoids were explored to control the formation of the GNPs. The synthesized GNPs were characterized by UV–Vis spectroscopy, transmission electron microscopy and X-ray diffraction. Stability and catalytic activity of the synthesized GNPs were also discussed. The results showed that the synthesized GNPs were in spherical, about 2.6 nm, with a face centered cubic structure. Synthesized GNPs showed good catalytic activity in the reduction of p-nitrophenol (p-NP) to p-aminphenol (p-AP). This method for synthesis of GNPs is simple, economic, nontoxic and efficient.     

The separation and determination of nitrophenol isomers by high-performance capillary zone electrophoresis

o-Nitrophenol, m-nitrophenol, and p-nitrophenol could well be separated by capillary zone electrophoresis (CZE) by only adjusting the run buffer with methanol. Efficiency up to 10⁵ theoretical plates per meter was achieved. The effects of several important factors were investigated to find optimum conditions. The linear range, regression equation, and the recovery were given. This method possessed the advantages of simplicity, rapidity, and good reproducibility; it can be developed for the separation of practical samples in environment analysis.     

Nickel on Oxidatively Modified Carbon as a Promising Cost-Efficient Catalyst for Reduction of P-Nitrophenol

The reduction of p-nitrophenol to p-aminophenol has become a benchmark reaction for testing the efficiency of new catalytic systems. In this study, we use oxidatively modified carbon (OMC) as a structural support to develop a new cost-efficient nickel-based catalytic system. The newly developed material comprises single nickel ions, chemically bound to the oxygen functional groups on the OMC surface. The highly oxidized character of OMC ensures the high lateral density of nickel ions on its surface at relatively low nickel content. We demonstrate excellent catalytic properties of the new material by using it as a stationary phase in a prototype of a continuous flow reactor: the reagent fed into the reactor is p-nitrophenol, and the product, exiting the reactor, is the fully converted p-aminophenol. The catalytic properties of the new catalyst are associated with its specific morphology, and with high lateral density of active sites on the surface. The reaction can be considered as an example of single-atom catalysis. The resulting material can be used as an inexpensive but efficient catalyst for industrial wastewater treatment. The study opens the doors for the synthesis of a new series of catalytic systems comprising transition metal atoms on the OMC structural support.     

Local surface dipolar perturbation of lipid membranes by phloretin and its analogues

Concentration-response, electrolyte concentration and composition, and Arrhenius-Eyring energy in relation to changes in phosphatidyl choline-cholesterol membrane conductance have been studied to examine the adsorptive dipolar potential reduction caused by phloretin. The results indicate that these membranes possess weak surface binding sites for potassium ion. Calculations for a statistical local model of adsorption of phloretin molecules for each occupied cation site correlate with experimental trends. A rapid transient current resembling a capacitive charging effect was observed shortly after addition to one side of the membrane of phloretin and 2,4,6-trihydroxyacetophenone, but not for the dipolar species phlorhizin, p-nitrophenol or o-nitrophenol; the effect shows saturation characteristics.     

Decomposition reaction of organophosphorus nerve agents on solid surfaces with atmospheric radio frequency plasma generated gaseous species

The decomposition and detoxification of compounds are of great interest in environmental protection and defense-related areas. We report the generation of gaseous excited species by scanning atmospheric radio frequency (rf) plasma and their reactions with two representative organophosphorus nerve agents, paraoxon and parathion, deposited on solid surfaces. The excited gaseous species generated in the Ar and Ar/O2 plasma were identified as atomic oxygen, OH radical, and excited nitrogen molecule from optical emission spectroscopy analysis. The reaction of these species with paraoxon and parathion was monitored with reflection-absorption infrared spectroscopy and compared with the decomposition by UV irradiation and UV/ozone treatments. The decomposition products of the atmospheric rf plasma treatment were similar to those of the UV/ozone treatment. The atomic oxygen and excited OH species generated by the plasma appear to be responsible for the oxidation of paraoxon and parathion. The plasma-induced decomposition process was much faster and more efficient than the UV/ozone process. The complete detoxification of paraoxon and parathion upon a short time exposure to the Ar/O2 plasma was confirmed by the Drosophila melanogaster culture test.     

Determination of nitrophenolate sodium in aquatic products by HPLC–MS/MS with atmospheric pressure chemical ionization

The paper describes an efficient method for the determination of nitrophenolate sodium in aquatic products by HPLC combined with atmospheric pressure chemical ionization with tandem mass spectrometry (LC–APCI-MS/MS). Analytes were extracted from aquatic products by acetonitrile, the extracts were degreased by alumina and concentrated, the concentrated solution was further purified by Oasis HLB cartridge. Finally, the analytes were separated and detected by LC–APCI-MS/MS in negative ion mode. Excellent linearity with correlation coefficients of more than 0.995 was observed in the concentration range of 2–200 μg/L for p-nitrophenol sodium and 2-methoxy-5-nitrophenolate sodium, and 5–200 μg/L for ο-nitrophenol sodium. Recovery rates of nitrophenolate sodium between 86.1–94.3% were achieved. Limit of quantitation of p-nitrophenol sodium and 2-methoxy-5-nitrophenolate sodium was 2 μg/kg and ο-nitrophenol sodium was 5 μg/kg, with relative standard deviations <10%. This method was employed in the practical analysis of spiked and naturally contaminated aquatic products.