Properties and determination of pesticides in fruits and vegetables

The intensive development of agriculture means that more and more toxic organic and inorganic compounds are entering the environment. Because of their widespread use, stability, selective toxicity and bioaccumulation, pesticides are among the most toxic substances contaminating the environment. They are particularly dangerous in fruit and vegetables, by which people are exposed to them. It is therefore crucial to monitor pesticide residues in fruit and vegetables using all available analytical methods.We set out the problems in the determination of organonitrogen and organophosphorus pesticides in samples of fruit and vegetables, including the complexity and the diversity of matrices in biological materials, and the very low level of pesticides present, as a result of which target analytes have to be isolated and then enriched prior to final determination.We discuss the various stages in the determination of pesticide residues in fruit and vegetables. We present results from the literature in the context of Maximum Residue Levels (MRLs) of target pesticides in fruit and vegetable samples. We discuss the merits of the Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) technique and two-dimensional gas chromatography.     

速冻蔬菜中氯氰菊酯残留量的测量不确定度评定

依据GB/T 5009.146-2003《植物性食品中有机氯和拟除虫菊酯类农药多种残留的测定》方法,对速冻蔬菜中氯氰菊酯残留量的测量不确定度进行分析和评定。该测量过程所产生的测量不确定度主要来源于气相色谱仪引入的测量不确定度,其次是氯氰菊酯标准工作溶液引入的测量不确定度。标准溶液引入的测量不确定度则主要来源于标准溶液的稀释过程所产生的测量不确定度。     

Chromatographic determination of carotenoids in foods

In recent years, there has been particular emphasis on obtaining more accurate data on the types and concentrations of carotenoids in foods for various health and nutrition activities. The analysis of carotenoids is complicated because of the diversity and the presence of cis-trans isomeric forms of this group of compounds. In addition, a wide variety of food products of vegetal and animal origin, vegetables and animal samples contain carotenoids, and a great range of carotenoids can be found in these samples. The characteristic conjugated double bond system of carotenoids produces the main problem associated with work and manipulation on carotenoids, that is their particular instability, especially towards light, heat, oxygen and acids. For this reason, several precautions are necessary when handling carotenoids. Another problem associated with analysis of carotenoids is the difficulty in obtaining standard compounds. High-performance liquid chromatographic methods for the determination of carotenoids in foods are reviewed. The sample extraction and treatment, carotenoid purification and standard manipulation are briefly commented on. We present a critical assessment of chromatographic methods developed for the determination of carotenoids in foods. Finally, some methods for carotenoid ester separation are reviewed.     

Selective spectrophotometric determination of ascorbic acid in drugs and foods

A new analytical method was developed for the determination of ascorbic acid. The method is based on the reaction of ascorbic acid with 4-chloro-7-nitrobenzofurazane (NBD-Cl) in the presence of 0.2M sodium hydroxide, where a bluish green colour (lambda(max) 582 nm) is developed after dilution with 50% (v/v) aqueous acetone solution. Beer's law was obeyed in a concentration range of 5-20 microg ascorbic acid/ml with a good correlation coefficient (r = 0.9990). The method was found to be highly specific for the determination of ascorbic acid in the presence of dehydro-ascorbic acid, all other vitamins and minerals possibly present in multivitamin preparations, rutin, salicylamide, acetyl salicylic acid, paracetamol, caffeine, phenylephrine hydrochloride and dipyrone. Moreover, the proposed procedure was also successfully applied for the determination of ascorbic acid in some canned and fresh fruit juices, some vegetables and infant milk products without interference from coloured and other substances present in the plant extracts.     

悬浊液直接进样非火焰原子吸收法测定蔬菜样品中微量铬的研究

本文通过用直接悬浊液进样原子吸收法对新鲜蔬菜中铬的测定,研究了各种实验条件,并建立了实际测定新鲜蔬菜中微量元素的方法。该法将可用于食品。     

Selective trace determination of dithiocarbamate fungicides in fruits and vegetables by reversed-phase ion-pair liquid chromatography with ultraviolet and electrochemical detection

The predominant methods for determination of dithiocarbamate fungicides (DTC) have been based on quantitation of carbon disulfide released by hot acid digestion. Because the subgroups of the DTC family differ in their chemical properties and toxicological behavior, selective determination is required. To meet the demand for a fast, simple, and sensitive procedure, a new reversed-phase ion-pair chromatographic method was developed, consisting of surface extraction followed by direct injection into a liquid chromatographic system equipped with ultraviolet and electrochemical detectors, connected in series. The procedure is applicable to residues of N-methyldithiocarbamates (metam-sodium), N,N-dimethyldithiocarbamates (e.g., ziram and ferbam), ethylenebisdithiocarbamates (e.g., nabam, maneb, zineb, and mancozeb), and propylenebisdithiocarbamates (e.g., propineb) in fruits and vegetables. Limits of quantitation, calculated according to the procedure of the Deutsche Forschungsgemeinschaft, are 9, 12, 8, and 12 microg CS2/L for N-methyl-DTC, N,N-dimethyl-DTC, ethylenebis-DTC, and propylenebis-DTC, respectively, when electrochemical detection is used.     

Time-resolved characterization of laser-induced plasma from fresh potatoes

Optical emission of laser-induced plasma on the surface of fresh vegetables provides sensitive analysis of trace elements for in situ or online detection of these materials. This emergent technique promises applications with expected outcomes in food security or nutrition quality, as well as environment pollution detection. Characterization of the plasma induced on such soft and humid materials represents the first step towards quantitative measurement using this technique. In this paper, we present the experimental setup and protocol that optimize the plasma generation on fresh vegetables, potatoes for instance. The temporal evolution of the plasma properties are investigated using time-resolved laser-induced breakdown spectroscopy (LIBS). In particular, the electron density and the temperatures of the plasma are reported as functions of its decay time. The temperatures are evaluated from the well known Boltzmann and Saha-Boltzmann plot methods. These temperatures are further compared to that of the typical molecular species, CN, for laser-induced plasma from plant materials. This comparison validates the local thermodynamic equilibrium (LTE) in the specific case of fresh vegetables ablated in the typical LIBS conditions. A study of the temporal evolution of the signal to noise ratio also provides practical indications for an optimized detection of trace elements. We demonstrate finally that, under certain conditions, the calibration-free LIBS procedure can be applied to determine the concentrations of trace elements in fresh vegetables.     

高效液相色谱-串联质谱法测定植物源食品中四溴菊酯

建立了测定8种植物源食品中四溴菊酯残留的高效液相色谱-串联质谱分析方法。样品以乙酸乙酯为提取剂,经浓缩、净化,用流动相定容,采用高效液相色谱分离,以串联质谱在多反应监测模式下测定。结果表明,四溴菊酯质量浓度在20～1000μg/L范围内线性良好,相关系数为0.9998;在0.01、0.02和0.1 mg/kg(粮谷类样品)和0.005、0.01和0.05 mg/kg(果蔬类样品)添加水平下的回收率为81.6%～92.1%,相对标准偏差为4.0%～13%,定量限为0.01 mg/kg(粮谷类样品)和0.005 mg/kg(果蔬类样品)。     

Application of Reversed Phase Short End-Capillary Electrochromatography to Herbicides Residues Analysis

Reversed phase capillary electrochromatography was applied to the determination of phenylurea herbicides residues in different samples of vegetables and vegetable processed food. The use of 40% acetonitrile mobile phase content provided a large elution window and strongly reduced the presence of matrix interferences in real samples. The compounds were baseline resolved within 14 min with 97612–113312 N/m range by using the short end injection method. The method was repeatable and linear and applied to the analysis of spiked soya milk and canned soya shoots samples extracted after a reduced sample pretreatment procedure. The analysis of vegetables showed some difficulties arising from the complexity and the strong variability of the matrix.     

Determination of carbaryl, carbofuran and methiocarb in cucumbers and strawberries by monoclonal enzyme immunoassays and high-performance liquid chromatography with fluorescence detection. An analytical comparison

Carbaryl, carbofuran and methiocarb are three of the most important N-methylcarbamate pesticides. In the present work, the application of laboratory-developed monoclonal antibody-based enzyme-linked immunosorbent assays (ELISAs) to the determination of these compounds in fruits and vegetables is described. Cucumbers and strawberries were spiked with the three carbamates at 10, 50 and 200 ppb. After extraction and clean-up, samples were analyzed by immunoassay and by HPLC with post-column derivatization and fluorescence detection (US Environmental Protection Agency Method 531.1). Results obtained by ELISA correlated well with those obtained by HPLC, both in terms of accuracy and precision. Recoveries were in the 60-90% range by ELISA and in the 50-90% range by HPLC, depending on the particular combination of commodity, pesticide, and fortification level under consideration. ELISAs were also applied to the analysis of non-purified sample extracts with excellent results: recoveries close to 100% were obtained, while maintaining similar precision values. This approach avoids the use of solid-phase extraction columns, saves time, and considerably increases the sample throughput. Results clearly indicate that the developed immunoassays may be suitable for the quantitative and reliable determination of carbaryl, carbofuran and methiocarb in fruits and vegetables even without including clean-up steps. These considerations make these ELISAs very useful analytical tools for monitoring and regulatory programs, without the need of complex and expensive instrumentation.     

Phenomenological coefficients in the equations of thermodynamics of irreversible processes for anisotropic media

The phenomenological coefficients of the phenomenological equations (laws) obtained for anisotropic media, in particular, interphase separation regions, were studied. Generally, these coefficients are tensors of rank from 0 to 4. An attempt was made to find a general procedure for the determination of nonzero tensor components when cross phenomenological coefficient are present in phenomenological equations including generalized thermodynamic forces with various tensor ranks.     

Universal extraction/clean-up procedure for screening of pesticides by extraction with ethyl acetate and size exclusion chromatography

Size exclusion chromatography (SEC) is used as a clean-up procedure after extraction of pesticides with the compatible solvent ethyl acetate. Recoveries better than 90% are obained for oranochlorine and organophosphorus pesticides, fungicides and chlorobiphenyls from fats, fish oils, vegetables, fruits, cereals and liver. A comparison with other procedures is made. The use of a 10-mm i.d. SEC column provides the same limits of determination as those attainable with commercial systems by requires only 15% of the amount of solvents normally used.     

Methods for chromatographic determination of amanitins and related toxins in biological samples.

Methods for the chromatographic determination of amanitins, toxins of Amanita phalloides (Fr.), Link mushrooms and related toxins are reviewed; particular emphasis is given to high-performance liquid chromatographic methods. The main chemical and toxicological aspects are discussed, but the focus of the present review is on the analytical problems arising in a laboratory charged with the setting up of a procedure which can direct the appropriate clinical management of an intoxicated patient or solve a forensic case.     

Application of single-drop microextraction coupled with gas chromatography for the determination of multiclass pesticides in vegetables with nitrogen phosphorus and electron capture detection

In the present work the single-drop microextraction (SDME) technique coupled with GC-NPD and GC-ECD was evaluated for the determination of multi-class pesticides in vegetables. The donor sample solution preparation was optimized by testing different mixtures of solvents and dilutions with water. The SDME procedure was optimized by controlling drop organic solvent, drop volume, agitation, and exposure time. The optimum sample preparation was achieved with the use of a mixture of acetone/H(2)O (10/90, v/v) in donor sample solution preparation and the consequent SDME using a toluene drop under mild stirring for 25min. The efficiency of the extraction process was studied in fortified tomato and courgette samples and matrix effects were further estimated. The proposed method showed good linearity, limits of detection at the sub-microgkg(-1) level and high precision (RSD <15%) and was applied with success in real vegetable samples showing that SDME can be a promising way for sample preparation in pesticide residue analysis.     

Determination of polycyclic aromatic hydrocarbons in water by solid-phase microextraction and liquid chromatography.

This study describes the determination of polycyclic aromatic hydrocarbons (PAHs) in water using high-performance liquid chromatography (HPLC) coupled with fluorescence detection (FLD). Because individual PAHs are generally present in water only at trace levels, a sensitive and accurate determination technique is essential. The separation and detection of five PAHs were run completely within 25 min by the HPLC/FLD system with an analytical C18 column, a fluorescence detection, and acetonitrile-water gradient elution. Calibration graphs were linear with very good correlation coefficients (r > 0.9998), and the detection limits were in the range of 2-6 ng/l for five PAHs. Solid phase microextraction (SPME) was performed for sample pretreatment prior to HPLC-FLD determination, and the governing parameters were investigated. Compared to conventional methods, SPME has high recovery, saves considerable time, and reduces solvents waste. The extraction efficiencies of five PAHs were above 88% and the extraction times were 35 min in one pretreatment procedure. One particular discovery is that 1.5 M sodium monochloroactate (ClCH2COONa) can improve the extraction yield of PAH compounds more than other inorganic salts. The SPME-HPLC-FLD technique provides a relatively simple, convenient, practical procedure, which was here successfully applied to determine five PAHs in water from authentic water samples.     

Slurry-electrothermal atomic absorption spectrometric determination of aluminium and chromium in vegetables using hydrogen peroxide as a matrix modifier

Fast heating programmes for determining aluminium and chromium in vegetables using electrothermal atomic absorption spectrometry with slurry sampling are developed using wall atomization. The build-up of carbonaceous residues inside the atomizer is avoided by adding 4% hydrogen peroxide and 1% nitric acid to the slurries instead of using an air-ashing stage. In accordance with fast-programme methodology, the conventional drying and charring steps are replaced by a modified drying stage. simplifying the heating programmes. For suspensions containing 0.1% m/V of ground vegetables, the relative standard deviation (RSD) is about +/-5% for aluminium. For chromium determination, the use of 0.5-1% m/V suspensions leads to RSDs close to +/-4%. Calibration is carried out using aqueous standards. The aluminium and chromium contents of a number of vegetable samples obtained by using the slurry approach agree with those obtained by means of a conventional procedure based on the total dissolution of the samples. The reliability of the procedures is also confirmed by analysing two certified reference materials.     

Three-step extraction procedure for determination of heavy metals availability to vegetables

A three-step sequential extraction procedure was used to determine the concentration of heavy metal speciation forms in soil. The procedure allows one to identify the pool of heavy metals that can be potentially mobilised under changes in soil pH value or redox potential. It has been shown that similar portions of heavy metals are present in reducible, oxidisable and residual fractions. It was found that soil chemical properties significantly affected the distribution of heavy metals among different fractions and their uptake by vegetables. Cadmium was a dominant element which occurred in the exchangeable fraction—the most bioavailable and potentially toxic.     

Kinetic spectrophotometric determination of ascorbic acid by reduction of toluidine blue

A simple kinetic method is described for the determination of ascorbic acid. The procedure is based on the reduction of toluidine blue with ascorbic acid. The rate of reaction is followed by measuring the decrease in absorbance of toluidine blue (lambda(max) = 600 nm) as a result of its decolorization upon reduction by ascorbic acid. Ascorbic acid in the range of 3-35 microg/ml was determined using slope and fixed time methods of analysis, while the variable time method allowed the determination of 5-50 microg/ml of ascorbic acid. The percent relative standard deviation of the method varied from 0.78 to 1.32% depending on the kinetic method used. The high sensitivity of the method also allows determination of low levels of ascorbic acid in some fruits and vegetables such as dew melon, water melon, parsley and coriander.     

Determination of alpha-emitting isotopes of uranium and thorium in vegetables and excreta

A radiochemical procedure for the determination of alpha-emitting isotopes of uranium and thorium in vegetables and excreta has been optimized, involving sample dissolution, separation by ionic exchange resin, electrodeposition and alpha-spectroscopy. Uranium and thorium isotopes were determined separately to prevent interference of ²²⁸Th from ²³²U tracer with ²²⁸Th from natural series of 232Th. This procedure was applied to faeces from people living in the Poços de Caldas plateau, a high natural radioactivity region of Brazil, and vegetables from the Laboratory of Environmental Monitoring (EML/DOE). Results show a chemical recovery of 80–95% for uranium and 46–72% for thorium.     

Determination of dichlorvos by on-line microwave-assisted extraction coupled to headspace solid-phase microextraction and gas chromatography-electron-capture detection

The pretreatment technique of microwave-assisted extraction on-line headspace solid-phase microextraction (MAE-HS-SPME) was designed and studied for one-step in-situ sample preparation prior to the chromatographic analysis of a pesticide on vegetables. The pesticide on chopped vegetables was extracted into an aqueous solution with the aid of microwave irradiation and then directly onto the SPME fiber in headspace. After being collected on to the SPME fiber and desorbed in the GC injection port, the pesticide (dichlorvos) was analyzed with a GC-electron-capture detection system. The optimum conditions for obtaining extraction efficiency, such as the pH, the polarity modifier, and the salt added in sample solution, the microwave irradiation, as well as the desorption parameters were investigated. Experimental results indicated that the proposed MAE-HS-SPME technique attained the best extraction efficiency of 106% recovery under the optimized conditions, i.e. irradiation of extraction solution (10% aqueous ethylene glycol) at pH 5.0 with medium microwave power for 10 min. Desorption at 220 degrees C for 3 min offered the best detection result. The detection was linear at 5-75 microg/l with correlation coefficient of 0.9985. Detection limit was obtained at approximately 1.0 microg/l level based on S/N=3. The proposed method provided a very simple, fast, and solvent-less procedure to collect pesticides directly from vegetables for GC determination. Its application was illustrated by the analysis of trace dichlorvos in vegetables.