气相色谱——质谱法对土壤中多种农药残留的测定方法

用GC -MS法测定土壤中的农药残留物 ,快速准确 ,回收率 83 %～ 112 %,平均变异系数在 4.8%～ 15 .2 %之间。为科学监测、合理利用土壤资源提供了依据     

Degradation of 2,4-D By Ozone And Light

The decomposition of 2,4-dichlorophenoxyacetic acid in aqueous solutions has bsen studied using ozone and ultraviolet radiation at different pH, ozone production, and initial concentration of pesticide. A mathematical model which incorporates the rate of mass transfer of ozone, the oxidation kinetics of 2,4-D and the kinetics of formation and oxidation of the intermediates was used. A global rate constant was calculated and an empirical equation which correlated that constant with ozone production, initial concentration of 2,4-D and pH at the same temperature was determined.     

Photocatalytic treatment of water-soluble pesticides by photo-Fenton and TiO2 using solar energy

The technical feasibility and performance of photocatalytic degradation of four water-soluble pesticides (diuron, imidacloprid, formetanate and methomyl) have been studied at pilot scale in two well-defined systems of special interest because natural-solar UV light can be used: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. The pilot plant is made up of compound parabolic collectors (CPCs) specially designed for solar photocatalytic applications. Experimental conditions allowed disappearance of pesticide and degree of mineralisation achieved in the two photocatalytic systems to be compared. In order to assure that the photocatalytic results are consistent, hydrolysis and photolysis tests have been performed with the four pesticides. The initial concentration tested with imidacloprid, formetanate and methomyl was 50 and 30 mg/l with diuron, and the catalyst concentrations were 200 mg/l and 0.05 mM with TiO₂ and iron, respectively. Total disappearance of the parent compounds and 90% mineralisation have been attained with all pesticides tested, methomyl being the most difficult to be degraded with both treatments. First-order rate constants, initial rate, time necessary for mineralising 90% of the initial TOC and hydrogen peroxide consumption were calculated in all cases, enabling comparison both of treatments and of the selected pesticide reactivity.     

Detection of the residues of nineteen pesticides in fresh vegetable samples using gas chromatography–mass spectrometry

In this study, we investigated the presence of 19 different agricultural pesticides in 210 samples of eight types of domestic vegetables collected from several vegetable-growing regions in Bangladesh. A multiresidue method was developed to detect the pesticide levels in the collected samples using gas chromatography with mass spectrophotometry (GC–MS). Pesticide residues were detected in 51.30% of the total samples, and among the positive samples, 38.89% contained levels above the maximum residue levels (MRLs). The most frequently detected pesticides were chlorpyrifos (34) followed by carbofuran (17), diazinon (16), carbaryl (14), malathion (11), endosulfan (8), cypermethrin (7) and dimethoate (6). Some (10.47%) of the samples contained multiple residues. It is concluded that the continuous monitoring and strict regulation of pesticide use on food crops, especially vegetables, are necessary.     

Adsorption of MCPA pesticide by MgAl-layered double hydroxides

In the present study, the adsorption characteristics of the herbicide MCPA (4-chloro-2-methylphenoxyacetic acid) on layered double hydroxides (LDHs) were evaluated under laboratory conditions with particular attention to the effect of layer charge, original interlayer anion and morphology. The final objective is the use of LDHs and modified LDH materials as recyclable adsorbents and heterogeneous catalysts for the treatment of contaminated waste waters.The anionic clays tested were [Mg_1−xAl_x(OH)₂]^x+[X_x/m^m−·nH₂O] materials. The MCPA adsorption capacity was determined from adsorption isotherms and a kinetic study. We looked at the influence of the pH, the Mg²⁺/Al³⁺ ratio, i.e. the anion exchange capacity, the nature of the intercalated anion X (CO₃²⁻, NO₃⁻, Cl⁻) and the morphology of the adsorbent on the extent of adsorption. The adsorption isotherms, described by Freundlich model, are of S-type with tendency to L-type for high MCPA equilibrium concentration. Furthermore, the adsorption capacity increases with the layer charge density. Hence, MCPA adsorption on LDHs occurs by anion exchange in two steps, an external exchange followed by an interlayer exchange, which explain these changes of type within the same isotherm. Besides, the adsorption capacity depends on the nature of the starting anions, following the affinity order (NO₃⁻<Cl⁻<CO₃²⁻) proposed by Miyata and increases with the specific surface area.     

Comparison between Ozonation and Photo-Fenton Processes for Pesticide Methomyl Removal in Advanced Greenhouses

So-called “Advanced Greenhouses” are a new approach to the concept of protected agriculture. Among other technological and structural improvements, these facilities give the possibility of recycling the irrigation surplus water, rich in lixiviates, salts, pesticides and its metabolites. After many cycles, the current is so concentrated on those substances that it becomes necessary for the presence of a membrane separation stage which brine, highly concentrated on those named pollutants, has to be treated before being sent to the public sewage system. Advanced Oxidation Processes, among other chemical treatments, can be considered an alternative to process this current effluent. In this work, concentrated aqueous solutions of methomyl as model pesticide (200 mg·L^?1) have been subjected to two of those processes: ozonation and photo-Fenton reaction. Analysis of the elimination of the pesticide itself and the grade of mineralization achieved have shown how, while the ozonation is the most effective process decomposing the pesticide (eliminating the total concentration in 60 minutes), the photo-Fenton reaction mineralizes successfully the 40% of the total organic load (the ozonation only can cope with 20%) but only decompose a 40% of the pesticide. Evolution of biodegradability and toxicity of the effluent along both processes was also analyzed. Intermediates generated both by ozonation and photo-Fenton did not increase the biodegradability of the treated effluents. Nevertheless, while acute toxicity just after 15 minutes of treatment with ozone is notably higher than for raw solution, and it is maintained till the end of the experiment (120 min), though, toxicity along photo-Fenton reaction has two growing and decreasing regions, always shows lower values than the provoked during ozonation. None of the two assayed processes has been proved to increase biocompatibility of highly concentrated methomyl solutions.     

Pesticide residue analysis by RPLC–GC in lycopene and other carotenoids obtained from tomatoes by supercritical fluid extraction

In the present work supercritical fluid extraction (SFE) is used to obtain carotenoids from tomatoes which were previously treated with pesticides. A procedure to determine pesticides in the extracts by RPLC–GC using the TOTAD interface is proposed. Tomatoes growing in an experimental plot were treated with different pesticides, and after picking, pesticide residues in the tomatoes were analysed and the tomatoes were used to obtain carotenoids by SFE. The carotenoid extracts were analysed using the above mentioned method. The data obtained indicated that trace amounts of the pesticides were extracted together with the carotenoids by SFE. The concentration of pesticide obtained in the second separation vessel was higher than that obtained in the first separation vessel. We conclude that only pesticide-free tomatoes should be used to extract carotenoids for applications as a nutritional supplement or in the cosmetic and pharmaceutical industries.     

An overview of solid‐phase extraction of food flavor compounds and chemical residues

Abstract

Solid‐phase extraction (SPE) is a rapid and sensitive sample preparation technique whose use has increased considerably within the last decade. This emerging technology has successfully replaced many tedious conventional methods of isolation and extraction of various chemicals in food, environmental, pharmaceutical, and biological samples. Sample preparation and concentration via SPE can be achieved in a one‐step extraction, and the methodology is appropriate for isolating trace amounts of chemical compounds from complex matrices. This paper gives an overview on the use of SPE as a sample preparation tool for the isolation of flavor compounds and chemical residues in food. Applying SPE in the areas of food science and agriculture will be valuable in assuring the safety and quality of our food products.     

A reliable screening of mycotoxins and pesticide residues in paprika using ultra-high performance liquid chromatography coupled to high resolution Orbitrap mass spectrometry

In this study, an ultra-high performance liquid chromatography (UHPLC) coupled to a high resolution Orbitrap mass spectrometry (Orbitrap-HRMS) was demonstrated as a promising technique in high-throughput method development for the routine analysis and contamination control of mycotoxins and pesticide residues in spices. The method was applied for the analysis of fifty ground paprika samples containing blends of sweet and hot paprika harvested in Brazil and China. The efficiency and detection sensitivity of the used UHPLC-Orbitrap-HRMS technique were compared to the results obtained using a triple quadrupole tandem mass spectrometric detector (UHPLC-QqQ-MS/MS). The values of recovery (75–120%) and repeatability (8–15%) for both methods, calculated as the average (n = 5) from the results of spiked (10–500 μg kg⁻¹), paprika samples, were in good conformity to the relevant EU guidelines. The high resolution of the used Orbitrap-HRMS technique provided a better sensitivity for quantitative determination of several pesticide contaminants in paprika, compared to the results obtained by the QqQ-MS/MS method and were comparable in case of mycotoxins. The results of analysis demonstrated the ubiquitous presence of three mycotoxins (fumonisin B₁, ochratoxin A, and sterigmatocystin) and twelve pesticide residues in paprika. The concentrations of determined contaminants were below the MRLs set by the Regulations of the European Union with exception of iprovalicarb, which violated the EU MRL in two samples of hot paprika. In addition, a notable difference in the concentration of fumonisin B₁ was determined depending on the harvest period (2009–2013), reaching the maximum concentrations of 33 μg kg⁻¹ in sweet paprika and 140 μg kg⁻¹ in hot paprika. There was no significant correlation found between the determined mycotoxin contamination levels and the pesticide residues, with the sole exception of decreased fumonisin B₁ content in samples with an elevated concentration of metalaxyl fungicide.     

Pilot Plant Results with Three Different Types of UV Lamps for Advanced Oxidation

Three different types of ultraviolet lamps were tested for the advanced oxidation process application on pre-treated surface water in a pilot plant. The pilot setup consisted of three parallel reactors with either medium pressure, low pressure or dielectric barrier discharge UV lamps. Four model compounds (atrazine, bromacil, ibuprofen and N-nitroso-dimethylamine (NDMA)) and 0, 5 or 10 ppm hydrogen peroxide were dosed. Low pressure lamps were shown to have the lowest energy demand, calculated as electrical energy per order, followed by dielectric barrier discharge lamps and then medium pressure lamps. Medium pressure lamps gave the highest formation of genotoxic activity and nitrite formation, whereas no formation of genotoxic activity was observed for either of the other lamp types.