Pure pesticides

A two-step laboratory thermal-decomposition analytical system involving vaporization and thermal destruction was developed in 1975 by the University of Dayton Research Institute for EPA (6). Vaporization of pure pesticide occurred at 200 to 300°C and was followed by decomposition in a quartz tube at temperatures exceeding 900 C. The destruction efficiencies for DDT, Kepone, and mirex exceeded 99.99% at 2-s residence time and greater than 900 C. 

Pesticides applied indoors vaporize from treated surfaces (e.g. carpets and baseboards) and can be resuspended into air on particles. Many pesticides are semivolatile (saturation vapor pressures between 10 kPa and 10 kPa at 25 °C) and tend to vaporize from treated indoor surfaces. The rate of volatilization will depend on the vapor pressure of the compound, the formulation (solvent, surfactants, microencapsulation, etc.), the ambient and surface temperatures, indoor air movement and exchange rates (ventilation), the type of surface treated and the elapsed time after application. The vapor pressure data for pure pesticides is frequently available and may be of value for assessing the relative importance... 

Each laboratory prepared separate calibrants according with their own laboratory procedure. These were used for calibrating the detector within its dynamic range. Calibrants were prepared, avoiding serial dilution. A minimum of five calibration points were required. The coordinator supplied the participants with pure pesticides samples with certified purity. The participants were requested to use these calibrants or to check their own calibrants. For GC and HPLC analysis at least one internal standard was used for the final determination. 

Lindane is one of eight different hexachlorocyclohexane (HCH), C H Cl, isomers and its Chemical Abstract n.2cniQ is la, 2a 3P, 4a, 5a 6P-hexachlorocyclohexane [58-89-9] (y-HCH or y-BHC, ben2ene hexachloride) (80). Commercial products containing lindane are marketed as either a mixture of isomers or as the pure y-BHC isomer. Not unexpectedly, lindane is a highly stable lipophilic compound and it has been used extensively worldwide as an insecticide. In contrast, hexachloropentadiene, C Cl, is an extremely reactive industrial intermediate used as a chemical intermediate in the synthesis of a broad range of cyclodiene-derived pesticides, which include endosulfan, endrin, heptachlor, and several different organohalogen flame retardants (81). 

Soxhlet thimbles and filter papers may contain traces of lipid-like materials. For manipulations with highly pure materials, as in trace-pesticide analysis, thimbles and filter papers should be thoroughly extracted with hexane before use. 

Only particular solvents are suitable for certain purposes. The choice depending, for instance, on their residual water content or their acid-base nature if Rf values are to be reproduced [1, 2]. Halogen-containing solvents may not be employed for the determination of chlorinated pesticides. Similar considerations apply to PAH analyses. Pro analyst grades are no longer adequate for these purposes. It is true that it would be possible to manufacture universally pure solvents that were adequate for all analytical purposes, but they would then be too expensive for the final user [3, 4]. 

Methyl parathion is a pesticide that is used to kill insects on crops. Usually, it is sprayed on the crops. Methyl parathion comes in two forms a pure form of white crystals and a technical-grade solution (brownish liquid), which contains methyl parathion (80%) and inactive ingredients in a solvent. The technical-grade methyl parathion smells like rotten eggs or garlic. Methyl parathion is a manufactured chemical, so it is found in the environment only as a result of its manufacture or use. Methyl parathion has been manufactured in the United States since 1952 and has been used to kill insects on many types of crops since this time. Because methyl... 

When pure P-endosulfan was allowed to equilibrate in the apparatus, the ratio of the P-isomer to the a-isomer in the gas phase became 8 92 at 20 , suggesting that the P-isomer converts to the a-isomer (Rice et al. 1997). Several investigators have reported rapid initial losses of endosulfan residues from treated plant surfaces due to volatilization (Archer 1973 Terranova and Ware 1963 Ware 1967). One research group (Willis et al. 1987) attributed the limited runoff losses found in soybean fields treated with endosulfan to early losses of the compound during application and to volatilization/degradation of the compound from plant surfaces. Air sampling performed in a wind tunnel under defined conditions (20 air velocity 1 m/sec relative humidity 40-60%) showed that 60% of the initial dose of endosulfan is volatilized from Trench bean surfaces after 24 hours (Rudel 1997). Influences of various pesticide application formulations were not tested. 

Chlorinated dibenzo ip-dioxins are contaminants of phenol-based pesticides and may enter the environment where they are subject to the action of sunlight. Rate measurements showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is more rapidly photolyzed in methanol than octachlorodi-benzo-p-dioxin. Initially TCDD yields 2,3,7-trichlorodiben-zo-p-dioxin, and subsequent reductive dechlorination is accompanied by ring fission. Pure dibenzo-p-dioxin gave polymeric material and some 2,2 -dihydroxybiphenyl on irradiation. Riboflavin-sensitized photolysis of the potential precursors of dioxins, 2,4-dichlorophenol and 2,4,5-trichloro-phenol, in water gave no detectable dioxins. The products identified were chlorinated phenoxyphenols and dihydroxy-biphenyls. In contrast, aqueous alkaline solutions of purified pentachlorophenol gave traces of octachlorodibenzo-p-dioxin on irradiation. 

Nitrosamines and Pesticides A Special Report on the Occurrence of Nitrosamines as Terminal Residues Resulting from Agricultural Uses of Certain Pesticides (10), P. C. Kearney, Project Coordinator, Pure and Appl. Chem.,... 

A limited number of pure substances are available from NIST, primarily clini-cally-relevant compounds such as cholesterol, urea, uric acid, creatinine, glucose, cortisol, tripalmitin, and bilirubin (NIST SRM website). These compounds are certified for purity (greater than 99 %) and are used as primary calibrants in definitive methods for these clinical analytes (see below). Several additional pure substances are available for specific applications such as microchemistry, i.e. elemental composition (acetanilide, anisic acid, cystine nicotinic acid, o-bromobenzoic acid, p-fluoro-benzoic acid, m-chlorobenzoic acid), polarimetric standards (sucrose and dextrose), acidimetric standard (benzoic acid and boric acid). Only three pure substance NIST RMs are available for environmental contaminants, namely the chlorinated pesticides, lindane, 4,4 -DDT, and 4,4 -DDE. 

Calibration data (e.g., linearity or sensitivity) are not discussed in detail between laboratories, but a typical calibration starts with 50% of the lowest fortification level and requires at least three additional calibration levels. Another point of calibration is the use of appropriate standards. In 1999 a collaborative study tested the effect of matrix residues in final extracts on the GC response of several pesticides.Five sample extracts (prepared for all participants in one laboratory using the German multi-residue procedure) and pure ethyl acetate were fortified with several pesticides. The GC response of all pesticides in all extracts was determined and compared with the response in the pure solvent. In total, 20 laboratories using 47 GC instruments... 

The following analytical standards were synthesized by Monsanto Company and may be available through the Environmental Protection Agency, National Pesticide Standard Repository (Fort Meade, MD, USA) [l-(methylethyl)phenylamino] oxoacetic acid, sodium salt, >95% pure (NIPA-producing metabolite) and N-isopropylaniline (NIPA), >99% pure. 

R.H. Shimabukuro, G.L. Lamoureux, D.S. Frear, and J.E. Bakke, in Metabolism of s-Triazines and Its Significance in Biological Systems, ed. A.S. Tahori, Pesticide Terminal Residues (Supplement to Pure and Applied Chemistry), Butterworth, London (1971). 

Bates, J.A.R. (1990) The prediction of pesticide residues in crops by the optimum use of existing data, Pure/Appl. Chem., 62 337-350. 

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