UV-visible absorption spectra and luminescence of the pesticide fenarimol

The UV-visible absorption and emission spectra have been measured of the pesticide fenarimol ((±)-2,4′-dichloro-α-(pyrimidin-5-yl)-benzhydryl alcohol) in solution. From comparison with the spectra of chlorotoluenes and pyrimidine, and from the effect of solvent polarity on the absorption spectrum, it is shown that the lowest excited singlet state is localized on the pyrimidine ring, and has n,π* character. Higher excited π,π* states are localized on both chlorotoluene and pyrimidine rings. Fenarimol shows a weak, fluorescence from the n,π* state, with a quantum yield which is strongly dependent on solvent. It is shown that this is due to changes in the nonradiative decay rate, particularly in protic solvents, due to increased intersystem crossing. Phosphorescence is observed in low temperature glasses. Although this shows two decay components, it is suggested that only one triplet state is involved, and that this has predominantly π,π* character.     

Dielectric studies of photodegradation and photooxidation of polystyrene

The effects of vacuum photolysis at 254 nm and the short-(λ = 254 nm) and long-wave (λ > 300 nm) photooxidations on the dielectric constants (?′) and dielectric losses (?″) of polystyrene have been investigated at 25 ± 1°C. Dielectric constants generally increase on photodegradation, but more pronounced increases occur in the low-frequency region on vacuum photolysis. It is suggested that such increases are associated with Maxwell-Wagner-Sillars polarization. Increases in dielectric losses are observed in three main frequency regions: around 10² Hz, 10⁴ Hz, and at 3 × 10⁶ Hz. The lowest frequency loss which occurs in both the vacuum-irradiated and in the photooxidized samples is attributed to a combination of the effects of interfacial polarization and of the increased direct-current conductivity of the polymer which occurs as a result of these reactions. The 10⁴ Hz dispersion associated only with photooxidation is related to the presence of small, volatile, polar oxidation products, like ketones. The loss peak overlaps the intrinsic γ-relaxation of polystyrene, and it appears that the motions of small molecules, or of relaxing dipoles in these, are coupled to the phenyl group rotational vibrations. The high-frequency losses (3 × 10⁶ Hz) are ascribed to orientation polarization of carbonyl dipoles attached to chain ends, these compounds being produced as a result of hydroperoxide decompositions. A good correlation between the carbonyl dipole relaxation strength and carbonyl concentration is observed. It would appear that relaxation strength measurements could provide quantitative kinetic information for polystyrene oxidation.     

Chemiluminescent determination of the pesticide bromoxynil by on-line photodegradation in a flow-injection system.

A new, robust and simple method is proposed for the chemiluminescent determination of the pesticide Bromoxynil. The empirical procedure is performed with the aid of a flow-injection manifold provided with an on-line photo-reactor to obtain chemiluminescent photofragments. After a period of 12 s of irradiation with an 8 W low-pressure mercury lamp, a chemiluminescent oxidation was performed with the system potassium permanganate in a polyphosphoric acid medium. The photolysis required a basic medium (KOH 0.014 mol l(-1)) with ethanol (1%) as a sensitizer. The method allowed the determination of 134 samples (h-1) of Bromoxynil in a wide interval of concentrations, over the range 5 x 10(-3) - 1 mg l(-1); the detection limit was 5 x 10(-3) mg l(-1). The RSD (n=24) at 0.25 mg l(-1) of the pesticide level was 2.3%. The method was applied to a water sample and to a formulation.     

Investigation of norflurazon pesticide photodegradation using plasma desorption time-of-flight mass spectrometry analysis

We have previously demonstrated that PD-TOFMS (plasma desorption time-of-flight mass spectrometry) analysis is a powerful technique for the in situ analysis of pesticides deposited or adsorbed on solid materials. With the aim of producing reproducible data on the modification of a pesticide under controlled photodegradation conditions, we have now undertaken a study where both the substrate and the pesticide are well characterized. This is the case for norflurazon deposited onto an aluminium substrate, in particular regarding the reproducibility of preparation of the samples and the change with time of their chemical composition. Degradation parameters have been derived from the variation in yield of ions representative of the molecule and of its breakdown products and, particularly, from the time required for 50% dissipation of their initial concentration (DT50). DT50 values ranging between 1 and 10 h have been found. An interpretation of the degradation process is proposed from the decay of other ions. As expected, the degradation is faster when the UV sunlight is unfiltered (a factor of 3.8 for the molecule, and around 5 for the breakdown products).     

Kinetic studies on fluvastatin photodegradation in solutions

Summary The effect of solvent on the photodegradation kinetics of fluvastatin was evaluated. The degradation rate of fluvastatin was estimated on the basis of the quantum yields and kinetic parameters determination. The photodegradation appeared to follow first-order kinetics. In order to establish the light intensity absorbed by a system, Reinecke’s salt was used as a chemical actinometer.     

ESR studies of the photodegradation of polyethylene containing trapped allylic free radicals

Changes produced in γ-irradiated polyethylene by subsequent ultraviolet irradiation have been investigated by ESR measurements, ultraviolet spectroscopy, and viscometric determination of average molecular weight. The photoinduced changes depend on the wavelength of irradiation. Upon irradiation at wave length greater than 3900 Å, main-chain scission occurs by reaction of trapped allylic radicals: A reduction in molecular weight sndicated by this reaction was verified by fractionation experiments and molecular weight determinations.     

Study of photodegradation of the pesticide ethiofencarb in aqueous and non-aqueous media, by gas chromatography–mass spectrometry

A comparative photodegradation kinetic study of ethiofencarb [2-ethylthiomethyl(phenyl)-N-methylcarbamate] in aqueous and non-aqueous media (hexane and methanol), is carried out. After irradiation, the aqueous samples are extracted with isobutyl methyl ketone. Ethiofencarb and its metabolites are analyzed by GC in combination with nitrogen–phosphorus detection and MS, respectively. The degradation kinetics depend on the solvent polarity; the quickest pesticide transformation is in the aqueous medium and the slowest in hexane. The photoproducts are also dependent on the solvents. In the case of the aqueous solution, photocleavage of the carbon–sulphur bond gives 2-(methyl)phenyl-N-methylcarbamate as the main product, while methanol and hexane solutions show different photoproducts.     

Evaluation and optimisation of methylene blue removal measurement uncertainty in photodegradation studies

Accreditation and Quality Assurance - The photodegradation of carcinogenic and teratogenic organic contaminants, such as active substances of medicines or preservatives of personal care products,...     

Practical fast gas chromatography for contract laboratory program pesticide analyses

An approach to shortening the analysis time for practical fast gas chromatography (GC) by using Method Translator software, which can be downloaded free from the Internet, is presented. This software simplifies the process of optimizing temperature programming while changing column dimensions, carrier gas type, and flow. Basic chromatographic theory is employed in a practical manner for adjusting column dimensions for optimal performance. In addition, electronic pneumatic control and high oven ramp rates make it easier to achieve fast analysis times without reproducibility problems. This practical approach is demonstrated using Contract Laboratory Program pesticide analytes. The factors found to be most important in decreasing the analysis time without a loss of performance are utilization of GC columns having smaller diameters and substitution of hydrogen for helium as the carrier gas.     

GC/MS studies on revealing products and reaction mechanism of photodegradation of pesticides

The photolytic degradation of frequently applied s-triazine type pesticides was investigated. A special, immersible UV-light source was applied in order to carry out photodegradation. The degradation processes were followed by TLC, GC and GC/MS techniques. Following the irradiation of the sample, the degradation products were isolated by SPE column chromatography. EI mass spectrometry was used to identify the degradation species.All four of the different s-triazine type pesticides studied underwent photolytic decomposition. The kinetic aspect of photodegradation of prometryn, terbutryn, simazine and atrazine was revealed completely, while in case of prometryn and terbutryn a detailed mechanism of photolytic transformation was established. Four degradation species were detected, as a consequence of two parallel ways of degradation. Both pesticides suffered the loss of thio-methyl groups prior to cleavage of the alkyl groups. Deamination did not occur under the conditions applied. The kinetic behaviour with respect to photodegradation displayed significant differences when comparing the decomposition of s-triazine type pesticides: prometryn decomposed 10 times faster than terbutryn.     

Voltammetric studies of the interaction between lead metal ion and the methyl parathion pesticide

Journal of Solid State Electrochemistry - In this work, the interaction of the pesticide methyl parathion (MP) with the lead metal ion was evaluated using a carbon electrode reused from a zinc...     

Experimental and theoretical studies on the photodegradation of 2-ethylhexyl 4-methoxycinnamate in the presence of reactive oxygen and chlorine species

2-Ethylhexyl 4-methoxycinnamate (EHMC) is one of the most commonly used sunscreen ingredient. In this study we investigated photodegradation of EHMC in the presence of such common oxidizing and chlorinating systems as H₂O₂, H₂O₂/HCl, H₂O₂/UV, and H₂O₂/HCl/UV. Reaction products were detected by gas chromatography with a mass spectrometric detector (GC-MS). As a result of experimental studies chloro-substituted 4-methoxycinnamic acid (4-MCA), 4-methoxybenzaldehyde (4-MBA) and 4-methoxyphenol (4-MP) were identified. Experimental studies were enriched with DFT and MP2 calculations. We found that reactions of 4-MCA, 4-MBA and 4-MP with Cl₂ and HOCl were in all cases thermodynamically favorable. However, reactivity indices provide a better explanation of the formation of particular chloroorganic compounds. Generally, those isomeric forms of mono- and dichlorinated compounds which exhibits the highest hardness were identified. Nucleophilicity of the chloroorganic compounds precursors were examined by means of the Fukui function.      

Determination of photodegradation and ozonation by products of linear alkylbenzene sulfonates by liquid chromatography and ion chromatography under controlled laboratory experiments

A Suntest solar simulator with arc xenon lamp was used to irradiate pure linear alkylbenzene sulfonates (LAS) standard and some commercial LAS solutions. The ozonation treatment was carried out in a pilot plant air-lift type reactor. Kinetic degradation curves were obtained showing an apparent first order reaction in both cases. Extraction and preconcentration of samples was carried out by off-line SPE using polymeric an RP-18 cartridges with recoveries varying from 77 to 93% for the LAS compounds. For LC chromatographic elution of LAS and degradation products an ion pair based on 5 mM triethylamine and 5 nM acetic acid had to the acetonitrile-water or methanol-water mobile phases. Fluorescence detection was achieved at 225 and 295 nm as excitation and emission radiation wavelength, respectively. Degradation by products were identified by liquid chromatography electrospray mass spectrometry detection (LC-ESI-MS). Ion chromatography (IC) was used to analyze refractory species such as oxalate, formate and acetate ions which were present in the treated solution even after 3 h of ozone treatment. The LAS mixture was almost totally degraded in less than 20 min using O₃/H₂O₂, the reaction being faster than in the case of catalyzed photodecomposition. TOC removal reached 84% after 3 h of ozonation process.     

A batch membrane reactor for laboratory studies

A membrane reactor consisting of two recirculating flow systems connected via a membrane module has been constructed and used to study the dehydrogenation of cyclohexane. When the reactor is operated differentially it is possible to obtain the same information that is generated when using more conventional steady flow reactors. The batch system has the advantages of easily varying the ratio of membrane area to reactor volume and sampling a very wide range of effective Damköhler numbers. These are important variables in design studies. This ability has been demonstrated for the dehydrogenation of cyclohexane. The batch system reproduced results from studies using a more conventional flow reactor. In addition, with the batch reactor it was possible to experimentally confirm predictions that were based upon computer simulation but which were outside the range of experimental study for the conventional reactors used.     

Photochemical studies on a phenolic phenylcoumarone lignin model molecule in relation to the photodegradation of lignocellulosic materials. Part 2. Photophysical and photochemical studies

The structure of the photoproducts obtained by irradiation of a phenylcoumarone molecule PCO, model of the photodegradation of lignin, being established, the mechanism of their formation was approached by fluorescence and flash photolysis techniques, low temperature absorption spectroscopy in rigid matrix, and continuous irradiation in solution and in the solid state. Some evidence was given for the formation of a phenoxy radical leading either by oxidoreductive processes to the formation of a catechol IR3, or by coupling with the starting phenol to the generation of a cyclobutane radical dimer, prone to be transformed into stilbene phenoxy radical by retro “2π+2π” reaction. It was proposed that the oxidation of the latter could give the very coloured quinone methide IR1 or the α-carbonylstilbenol IR2. The singlet manifold appears to be the main pathway of the production of IR1, IR2 and IR3 which are formed in the presence of ground state oxygen.     

An overview of laboratory performance studies conducted by the IAEA for marine pollution studies of metals and organic contaminants

Aspects of the International Atomic Energy Agency (IAEA) Analytical Quality Control Services (AQCS) for marine environmental studies are discussed, focusing on recent laboratory performance studies (LPS) and the production of reference materials for trace metals and organic compounds in various marine matrices. The IAEA has organized seventeen global interlaboratory studies for a range of organic contaminants. Of note has been the inclusion of numerous polychlorinated biphenyl congeners (PCBs) and some sterols of anthropogenic origin. Concurrently, there have been eleven worldwide intercomparison exercises for trace metals in the marine environment, most of which included methylmercury. Although such interlaboratory studies can help improve performance in individual laboratories and regional laboratory networks, the results reveal that problems remain in the determination of some metals and many organic contaminants.     

Environmental and ecological studies using proton activation analysis

Multielement analyses of environmental samples have been carried out using proton activation analysis. It has been shown that this technique is suitable for both the analysis of aerosol particulates collected on polystyrene filters and for the analysis of the roots of Eucalyptus trees. Aerosol particulates from around the eastern coast of Australia were found to contain S, Ca, Ti, Cr, Fe, Ni, Cu, Zn, Ga, Se, Sr, Y, Zr, Ru, Pt and Hg ranging in concentration from <0.003 to over 3.0 μg per cubic metre of air. A comparison between the ashed roots of healthy and diseased Eucalyptus trees from the Brisbane Ranges in Victoria showed that the concentrations of Fe and Ti in the diseased tree were only 30% and 59% respectively of that in the healthy tree.     

Utilisation of liquid chromatography in aquatic photodegradation studies of pesticides: A comparison between distilled water and seawater

Summary The advantages of liquid chromatography with diode array and mass spectrometric detection are described for the direct characterization of the photodegradation products of Fenitrothion, Atrazine and Diuron in distilled water and artifical seawater samples. The photodegradation (UV >290 nm) of the herbicides Atrazine and Diuron was examined in distilled water and in artificial seawater containing humic acids. Major photodegradation products were hydroxyatrazine and Monuron, respectively. The results showed a faster degradation in seawater as compared to distilled water for Atrazine whereas for Diuron a quenching effect was observed thus retarding photodegradation. The photodegradation of Fenitrothion was also investigated. For this pesticide, hydrolysis predominates in seawater and photolysis is very slow in distilled water, so that acetone was needed as photosensitizer.Presented at the 5th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region, Blanes, Spain, 2–6 October, 1989.