Sampling, extraction, cleanup and estimation of insecticide residue by various methods

Sampling, extraction, cleanup and estimation of insecticide residue by various methods

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  Sampling, extraction, clean-up and estimation of insecticide residues by various methods Presented By Aaliya Afroz Ph.D. Scholar Department of Entomology, IGKV, Raipur (C.G)
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  Introduction  When cropsare treated with pesticides very small amounts may remain in or on the crop after harvesting or storage.  In order to determine any pesticide residue present in foodstuffs analytical methods capable of accurately measuring extremely small amounts of pesticides are required.  Gas chromatography is the most used equipment in pesticide analysis others include High performance liquid chromatography (HPLC) .
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  Determination of PesticideResidue analysis involves 4 major steps- 1. Sampling 2. Extraction 3. Clean up 4. Analysis
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  1. Sampling:  Samplingcan be defined as the procedure or step adopted to obtain a representative quantity from the large consignment, so that selected representative quantity can be handled conveniently. a. Collection of samples b. Packaging and Transmission of laboratory samples c. Sub-sampling d. General Guidelines e. Compositing f. Homogenization of sample composite g. Sample storage h. Reserve storage
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  a. Collection ofsamples
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  2. Extraction:  Extractionis a fundamental process in pesticide residue analysis because no in-situ technique has yet been invented.  It is the process by which the toxicant is transferred from the treated bulky biological material into a solvent.  The selection of solvents depends on the physical and chemical properties of the toxicant which is to be extracted and on the type of substrate where it persists.
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  Methods for extraction: Surface Rinsing: This method is employed for the extraction of toxicant from the surface of the substrate.  Soxhlet Extraction: This method is employed for the extraction of dry samples.  Macerating & Blending: This method is used to remove the external and internal residues of insecticides from the treated biological material.
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  There are severalextraction approaches employed such as:  Pressurized liquid extraction(PLE)  Supercritical fluid extraction (SFE)  Solid-phase extraction (SPE)  Solid-phase micro extraction (SPME)  Microwave-assisted extraction(MAE)  Accelerated solvent extraction (ASE)  QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method  Matrix solid phase dispersion (MSPD)
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  3. Clean Up Isolation of toxicant from interfering substances or solvent is called clean up.  Clean-up is done to obtain uncontaminated products for analysis. Commonly Used Methods in Clean up (i) Steam Distillation (ii) Partition (iii) Sweep Co-Distillation (iv) Coagulation (v) Oxidation
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  4. Analysis  Theestimation of residues is possible by adopting any one of the analytical techniques. A. Chemical assay: The Commonly used chemical methods are 1) Spectrophotometric method 2) Ultraviolet Spectrophotometry 3) Visible spectrophotometry
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  Spectrophotometric methods:  Thistechnique utilizes the property of selective absorbtion of radient energy by chemical substances.  The quantitative analysis of insecticides in given samples is based on the Beer & Lambert’s law. Ultraviolet Spectrophotometry:  This method is used for the determination of residues of BHC, DDT, Diazinon and Parathion.  In this method the commonly used range is from 220 to 380 nanometers Visible spectrophotometry: This method is most commonly used in residue analysis. In this method the range used is from 400 to 600 nanometers.
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  Chromatographic Methods:  4types of Chromatographic methods are generally used in residue analysis. They are Column Chromatography:  Column chromatography in chemistry is a chromatography method used to isolate a single chemical compound from a mixture.  Chromatography is able to separate substances based on differential adsorption of compounds to the adsorbent; compounds move through the column at different rates, allowing them to be separated into fractions.
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  Paper Chromatography:  Itis an analytical method used to separate colored chemicals or substances[1]. It is primarily used as a teaching tool, having been replaced by other chromatography methods, such as thin-layer chromatography.  A paper chromatography variant, two-dimensional chromatography involves using two solvents and rotating the paper 90° in between. This is useful for separating complex mixtures of compounds having similar polarity, for example, amino acids.
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  Thin layer Chromatography: This technique is used in residue analysis for cleanup, Identification & quantification of some of the organochlorines, OPs and Carbamates. It is a chromatography technique used to separate non-volatile mixtures. Thin-layer chromatography is performed on a sheet of glass, plastic, or aluminium foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide (alumina), or cellulose.
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  IV. Gas Chromatography:
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  Gas-liquid chromatography GC-MS GC-MS is usually used in the analysis of mid- polar to non-polar compounds whereas HPLC technique used for polar compounds. Organophosphate and carbamate pesticides are mid polar in nature thus gas chromatography is well suited for their analysis. GC-MS systems are equipped with extensive mass spectral “libraries” that can be extremely useful for identification and characterization of unknown compounds.
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  Advances in pesticidesresidue analysis  Their has been a trend in advancement of analysis. Chromatography was the 1st invention back in 1906. Gas chromatography came into use in 1960 until late 1900. High performance liquid chromatography was later used in 1970- 1990 era. Gas chromatography mass spectrometry with advances came into use from 2000-to date.
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   In thismethod the living organisms are used for determining the insecticidal residues. Among insects, Drosophila, Adult house flies and larvae of mosquitoes are commonly selected as test insect. The primary disadvantage of this method is an inherent lack of specificity. B. BIO ASSAY: