HPLC Column Switching,a Step Toward the Automation of Sample Cleanup

Abstract

There exists a growing demand for data to meet the pesticide regulation acts and to monitor residues in food and in the environment. Speed and low running cost are very desirable properties of methods used to screen crops or commodities for pesticide residues, therefore evaluation of ways are necessary to carry out the analyses more rapidly and cost-effective. A today status of pesticide residue analysis is given. Weak points of the standard residue analytical procedures are shown. Trace enrichment and multidimensional liquid chromatography are the key-points which are prerequisites to scale down the sample size for the cleanup procedure. Reduction in scale on one hand and transfer of the individual cleanup steps, e.g. filtration, liquid-liquid partitioning, concentration, adsorption chromatography onto mini-columns or cartridges on the other hand, opens the potential to mechanize or automate the prechromatographic sample treatment.

Combination of all these different measures will reduce time and cost without the necessity to invest into expensive apparatus.     

Asulam in Aqueous Solutions: Fate and Removal Under Solar Irradiation

The photodegradation of the pesticide asulam (methyl[(4-aminophenyl)sulfonyl]carbamate) in aqueous solutions (1.0 2 10 m 4 mol L m 1 = 23 mg L m 1 ) has been investigated with and without Fe(III). The asulam disappearance were measured by direct photolysis at 254 nm as a function of pH and oxygen concentration. Different photoproducts have been identified, among them a blue condensation product which was only observed upon selective direct excitation of asulam. In the presence of Fe(III) and by excitation at 365 nm, we obtained the complete mineralisation of asulam, while no complete transformation of organic carbons into CO 2 was observed by direct photolysis. The continuous formation of ” OH radicals generated from the excitation of Fe(III) species allowed the total mineralisation of asulam. Information is also given about the fate of asulam in aqueous solutions under solar irradiation.     

Determination of Organophosphorus and Carbamic Pesticides with a Choline and Acetylcholine Electrochemical Biosensor

Abstract

Pesticides as paraoxon and aldicarb have been determined with an amperometric hydrogen peroxide based choline sensor. These pesticides inhibit the enzyme acetylcholinesterase which in presence of its substrate, acetylcholine, produces choline. When these pesticides are in presence of acetylcholinesterase, the activity of this enzyme decreases; this causes a decrease of choline production which is monitored by a choline sensor and correlated to the concentration of pesticide in solution. Two different procedures were followed: one with both the enzymes acetylcholinesterase and choline oxidase immobilized, the second one with the acetylcholinesterase in solution and the choline oxidase immobilized. Parameters as pH, buffer, enzyme concentration, substrate concentration and reaction and incubation times were optimized. Results showed that these compounds can be detected in the range 10 – 100 ppb. The use of the enzyme in solution gave the best results with a detection limit of 2 ppb pesticide.     

Trends of Pesticides in Norwegian Streams and Rivers (1996-2000)

In Norway twelve streams and medium size rivers have been monitored for pesticides in a four to six years period. During these years the central authorities have accomplished efforts to minimize the risk for pesticides entering the water bodies. Trend analyses have been done on the years 1996-2000 to gain information on whether there have been reductions in the retrieval of the pesticides: (1) Frequency of pesticides detection; (2) Sum concentration of all individual pesticides in each sample; (3) Environmental risk by weighing the concentration of each pesticide against the environmental maximum residue limits (MRL). As a whole, developments in streams and rivers show both positive and negative trends regarding the different parameters studied. The tendency is that the different parameters show the same development within the stream. The situation in these streams has not changed much during this 5 years period, but there are indications towards a slight positive development. Trend analyses might therefore be useful together with careful interpretation.     

Stocastic Measurement of Signals in Flame Atomic Absorption Spectrophotometry

Abstract

In flame atomic absorption spectrophotometry (US) there is usually more than one signal frequency for a given concentration when measured over a time interval. Certain elements have greater variability of signals than others. This study shows there is not much difference in correlation coefficients of a concentration and the mode and concentration and the arithmetic mean of the signals.     

Monoclonal Antibodies Useful in Sensitive Immunoassays for Aldicarb in Either Laboratory or the Field

Although polyclonal antisera have been used for immunodiagnostic measurement of aldicarb, both as components of commercial kits and as stand-alone products, no monoclonal antibody (MAb) reactive to this carbamate pesticide has yet been described. We have generated two MAbs with specificity to aldicarb, which function in our prototypic field immunoassays to identify this chemical in water samples. Further exploitation of these inherently stable immunoreagents should be valuable for point-of-need testing for the presence of aldicarb.     

A Comparison of Sample Preparation Techniques for the Determination of an Organo-phosphorous Pesticide from Water Using Reverse-Phase HPLC

Abstract

A methylene chloride liquid/liquid extraction and Sep-Pak C₁₈ cartridge adsorption techniques were used to quantify the pesticide, Dursban, in contaminated environmental water samples. Results showed a large disparity between Dursban levels using these two techniques, due primarily to the presence of a large adsorbed fraction of pesticide. A Sample Clarification Kit was used to isolate the particulate fraction, which can subsequently be stripped of its adsorbed pesticide compliment by means of a methanol rinse. Lastly, the filtrate from the Sample Clarification Kit may be trace enriched on a Sep-Pak C₁₈ cartridge to isolate the dissolved fraction of pesticide.     

Extraction and Detection of Pesticides by Cholinesterase Inhibition in a Two‐Phase System: a Strategy to Avoid Heavy Metal Interference

Abstract

A novel method of extraction has been developed to avoid the presence of heavy metals during the measurement of pesticides based on acetylcholinesterase (AchE) inhibition. Heavy metals have been in fact demonstrated in this article to interfere when the assay is performed by using the classic spectrophotometric Ellman's method. We present the results obtained with an assay system using two different phases, one organic and the other aqueous, in which the pesticide and the enzyme are, respectively, solubilized. In a first step, the concentration of the substrate acetylthiocholine (1 mM), of the enzyme (7 mU mL^?1), and the reaction time (20 min) for measurement of enzyme activity were optimized in aqueous solution. Next, the effect of an organic phase on the enzyme activity was studied by the addition of various solvents with the activity being evaluated after 10 min of mixing. It was found that by using hexane, the enzyme retained almost 100% of its activity, and this solvent was chosen for further development of the pesticide assay. Hexane was spiked with different concentrations of pesticides and then added to the enzyme aqueous phase. The pesticides were shown to be able to inhibit the enzyme by interaction at the interface between the two solutions. The degree of inhibition obtained with increasing amounts of pesticide was evaluated. A 50% inhibition was observed for a paraoxon solution of 9×10^?7 M.     

Preparation,Homogeneity and Stability of Polar Pesticides in Freeze-Dried Water Interlaboratory Exercise

Abstract

An interlaboratory exercise was carried out to improve the state of the art of some polar pesticide determination in water (atrazine, simazine, carbaryl, propanil, linuron, fenamiphos and permethrin). The preparation, the homogeneity and the stability of freeze-dried water samples containing the above pesticides was studied. The final concentration of each pesticide in water was in the 50–80 μg.^?1 range with a salt content of 2.5 g.l^?1 of NaCl. After the lyophilization the residue was reho-mogenised, filled into amber glass bottles and stored at -20 °C and +20 °C. Every three months, one sample was analysed to verify the stability of the residue.

All pesticides were determined by high performance liquid chromatography with diode-array detection (HPLC-DAD) except permethrin which was determined by gas chromatography with electron capture detection (GC-ECD).

The results obtained show that the atrazine, carbaryl, propanil, linuron and fenamiphos samples were homogeneously distributed, whereas simazine and permethrin were not. With respect to the stability over three months, all pesticides were stable at ?20 °C. Atrazine, simazine, carbaryl, propanil and linuron are also stable for the maximum storage time at +20 °C but the concentration of fenamiphos decreased by about 70% after one month.

The results obtained in the interlaboratory study by the participants were in good agreement for many of the pesticides.     

Development and Comparative Study of Different Immunoenzyme Techniques for Pesticides Detection

Abstract

Different ELISA techniques have been developed for the detemination of four widely used pesticides: 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), simazine and atrazine. Dependences between the assay scheme and the limiting detectable concentration of the pesticide were studied. The cases of preferential applying of the scheme with immobilized antibodies or one with immobilized pesticide-protein conjugate have been revealed. The following approaches resulting in lowering of ELISA sensitivity were proposed: preliminary incubation of the tested sample with antibodies, immobilization of antibodies via staphylococcal protein A, usage of monovalent fragments of antibodies instead of native ones and chemical modification of the pesticide molecules in the sample. Optimal combinations of these approaches permitted to lower the detection limit of the assays in about 5–30 times. The achieved sensitivities were 3 ng/mL for 2,4-D, 5 ng/mL for 2,4,5-T, 0.05 ng/mL for simazine, and 0.1 ng/mL for atrazine, being acceptable for purposes of ecological monitoring.     

Cloud point extraction as a sample enrichment technique for capillary electrophoresis–An overview

Abstract

Cloud point extraction (CPE) is a simple, inexpensive and green sample enrichment technique for different analytes in different matrices. In this technique surfactant solution is used at concentration above critical micelle concentration to extract the analytes from various matrices. Capillary electrophoresis (CE) and family of related techniques have emerged as powerful analytical techniques for pharmaceutical, biomedical, food and environmental analysis. In this review we have described the applications of CPE coupling with CE.     

Immobilization of Acetylcholinesterase onto Carbon Nanotubes Utilizing Streptavidin-biotin Interaction for the Construction of Amperometric Biosensors for Pesticides

Abstract

Carbon nanotubes (CNTs) are very promising materials onto which bioactive molecules can be immobilized in the construction of biosensors. Streptavidin was used as a molecular linker to immobilize biotinylated acetylcholinesterase (AChE) on CNTs in a gentle and controllable fashion for pesticide biosensors. Glassy carbon electrodes coated with the CNT-enzyme complex had high affinity for the substrate acetylthiocholine and produced strong peak oxidation currents in electrochemical assays. We also propose a new method, i.e., the use of relative net slope rather than the percentage of inhibition, in the calculation of pesticide concentrations. The biosensors could detect low levels of the pesticide methyl paraoxon.     

Treatment and Determination of Organophosphorous Pesticides in Waste Water by Using Continuous Flow Methodologies Coupled On Line With High Performance Liquid Chromatography

Abstract

The treatment of waste water containing three organophosphorous pesticides: diazinon, azinphos-methyl and fenthion by using continuous flow methodologies coupled on line with HPLC-UV detection is presented.

Two continuous flow techniques: completely continuous flow and flow injection, both combined with two separation methods: liquid-liquid extraction and adsorption resins are discussed, as well as the influence of physical and chemical parameters on the analysis.

Adsorption resins seem to be more suitalbe for the treatment of waste water at low pesticide concentraions while liquid-liquid extraction is more selective.     

Review of thin-layer chromatography in pesticide analysis: 2014–2016

ABSTRACT

Publications reporting techniques and applications of thin-layer chromatography (planar chromatography) for the separation, detection, qualitative and quantitative determination, and preparative isolation of pesticides and their metabolites are reviewed for the period from November 1, 2014 to November 1, 2016. Analyses are described for a variety of sample types and pesticide classes. In addition to references on residue analysis, studies such as pesticide chromatographic retention, identification and characterization of natural pesticides, metabolism, bioactivity, degradation, soil mobility, and lipophilicity are covered. The unique advantages of thin-layer chromatography in presenting results as a stored image on an open stationary phase are addressed.     

Evaluation of the Fate of Aldicarb and Its Metabolites in Oranges

Abstract

The accumulation, persistence and fate of systemic pesticide aldicarb was melencholy evaluated in orange crops. The concentration of this pesticide and its two toxic metabolites, aldicarb sulfoxide and aldicarb sulfone was determined in leaves, rind and pulp of three orange varieties (Satsuma, Navelina and Clemetina de Nules) and in the top soil of the orange groves. The groves were located in two different places in the Valencia Community (Spain). The analysis showed that the aldicarb concentration was lower than those of aldicarb sulfoxide and aldicarb sulfone. In all cases, the residues persisted at least 160 days in vegetable samples and between 157 and 227 days in soil samples. Residue concentrations measured in the soil samples were highly variable but a relation with the organic matter content can be observed. The residue levels found in vegetal products were higher in leaves than in rind, and in rind than in pulp. The maximum residue values were obtained between 47 and 70 days after the application. One hundred days after treatment (Security period) the residue levels of total fruit were lower than the maximum residue level of 0.2 mg/kg established by law.     

Determination of Morestan Residues in Water and Foodstuffs by Transmitted Room Temperature Solid Phase Spectrophosphorimetry

Abstract

A method for the determination of the pesticide morestan by means of transmitted room temperature solid phase spectrophosphorimetry has been developed. The method is based on the native phosphorescence showed by the morestan when it is fixed in a Whatman No 4 paper as a solid support. The excitation and emission wavelengths were 362 and 527 nm, respectively. The optimum phosphorescent emission was obtained when the delay time was 0.15 ms and the gate time 12.0 ms without need of a heavy atom. The linear dynamic range was between 0.1 and 1.0 μg.ml^?1, and the detection and quantification limits were 0.03 and 0.09 μg.ml^?1, respectively. The precision of the method, expressed as the relative standard deviation of ten samples at the 0.6 μg.ml^?1 concentration level, was 3.0%. The method was applied to the determination of the pesticide in different type of waters, potatoes and vegetables.     

Determination of the Concentration of Gases by Measurement of Pressure

Abstract

For the determination of the concentration of gases by means of pressure measurement, a precise equation of state is given by which analysis can be carried out within an accuracy of 10 ppm. The parameters of the equation of state are explicitely reported for carbon dioxide, argon, and helium.     

Application of Gas Chromatography‐Tandem Mass Spectrometry (GC‐MS‐MS) with Pulsed Splitless Injection for the Determination of Multiclass Pesticides in Vegetables

Abstract

GC‐MS‐MS was used to analyze vegetables for 14 pesticide residues. In the same run, the optimal ionization mode (electron ionization or chemical ionization) for each pesticide was selected. The method includes a simple extraction procedure with acetone and dichloromethane. A solid‐phase extraction tube was used for cleanup. The 1 µL of the final solution was injected into the instrument by pulsed splitless injection mode that can improve the sensitivity. The average recoveries were ranged from 78% to 102%. The relative standard deviation was lower than 18.4%. The calculated limits of detection were equal or lower than 0.02 mg/kg.     

Indirect Determination of the Pesticide Malathion by Atomic Absorption Spectrophotometry

Abstract

A method for the indirect determination of the pesticide malathion by atomic absorption spectrophotometry (AAS) is proposed and compared with the standard spectrophotometric method.

A study of the influence of the different variables on the hydrolysis and extraction is carried out in order to obtain the best experimental conditions.

The proposed method offers clear advantages over the standard procedure because of the instability of the Cu (II) complex formed. Both methods are applied to the determination of malathion in two commercial formulations.     

Wettability of ionic surfactants SDS and DTAB on wheat (Triticum aestivum) leaf surfaces

Abstract

Due to the important use of pesticide formulation, it is necessary to make it clear how ionic surfactant effect the wettability at leaf surface. In this work, we used the sessile drop method to study the wettability of SDS and DTAB on wheat leaf surfaces at different leaf stages, and reveal the relationship between surfactants structures and leaf stages of wheat leaf surfaces on wettability behavior. Results showed that few surfactant molecules adsorbed at the interface at low concentrations. With the concentration increased, the surfactant replaced the air layer partially within the nano/micro structure of leaf surfaces. When the concentration exceeded to CMC, the adsorption of surfactant molecules was saturated at both air-liquid interface and solid-liquid interface, the wetting state was still the transitional state between Cassie-Baxter’s and Wenzel’s state. In all concentrations, the adhesional tension and surface tension showed the linear relationship and the slope values were all below ?1, suggesting there were more surfactant molecules adsorbed at the solid-liquid interface than the liquid-air interface. As SDS is a common wetting agent and DTAB is a common fungicide in agrochemical, this study will provide potential guidance in practical application of pesticide solutions in leaf surface wetting.