Pesticide ionic

Miscellaneous Ionic Compounds. Also several other ionic pesticides exist which do not readily fall into the categories designated as cationic, basic, or acidic compounds. These compounds have weak acidic or basic... 

Benzonitriles. Although there are presently three benzonitrile herbicides used commonly, dichlobenil (Table XI) is the only one which is discussed here. Bromoxynil and ioxynil (Table IV) are hydroxybenzo-nitriles their hydroxy groups are ionizable, and they were discussed in Ionic Pesticides because of their acidic properties and low vapor pressures. 

Compounds less polar than pesticides that separate from pesticides in a rmre polar layer to a less polar one e.g., removal of lipids from acetonitrile extracts by LLP with hexane (loss of lipophilic pesticides) Ionic compounds from neutral pesticides or neutral compounds from ionic pesticides by pH adjustment in the aqueous layer... 

Just as surfactants may determine the mobility behavior of environmental chemicals in the soil, surfactant transport may also be influenced by other accompanying substances. For example, surfactants adsorbed on layer silicates may be exchanged by ionic pesticides, as illustrated in Fig. 18 for a clay mineral precoated with DTAB [20]. The preferentially adsorbed organic dication paraquat (PQ) displaces the single charged DTAB (the substance quantities are given in equivalent quantities (eq) to clarify the comparison). For each equilibrium concentration, the associated adsorbed amounts of PQ... 

Surfactants adsorbed on clays may be displaced by ionic pesticides, i.e., surfactant transport can also be influenced by other accompanying substances. 

The alkah flame-ionisation detector (AFID), sometimes called a thermionic (TID) or nitrogen—phosphoms detector (NPD), has as its basis the fact that a phosphoms- or nitrogen-containing organic material, when placed ia contact with an alkaU salt above a flame, forms ions ia excess of thermal ionic formation, which can then be detected as a current. Such a detector at the end of a column then reports on the elution of these compounds. The mechanism of the process is not clearly understood, but the enhanced current makes this type of detector popular for trace analysis of materials such as phosphoms-containing pesticides. 

Non-ionic surfactants used in detergents, paints, herbicides, pesticides and plastics. Breakdown products, such as nonylphenol and octylphenol, are found in sewage and industrial efffuents Products of combustion of many materials Widely used as plasticisers for PVC. Common environmental pollutants... 

Residue analytical chemistry has extended its scope in recent decades from the simple analysis of chlorinated, lipophilic, nonpolar, persistent insecticides - analyzed in the first Si02 fraction after the all-destroying sulfuric acid cleanup by a gas chro-matography/electron capture detection (GC/ECD) method that was sometimes too sensitive to provide linearity beyond the required final concentration - to the monitoring of polar, even ionic, hydrophilic pesticides with structures giving the chemist no useful feature other than the molecule itself, hopefully to be ionized and fragmented for MS or MS" detection. 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

KoC is an important parameter which describes the potential for movement or mobility of pesticides in soil, sediment and groundwater. Because of the structural complexity of these agrochemical molecules, the above simple relationship which considers only the chemical s hydrophobicity may fail for polar and ionic compounds. The effects of pH, soil properties, mineral surfaces and other factors influencing sorption become important. Other quantities, KD (sorption partition coefficient to the whole soil on a dry weight basis) and KqM (organic matter-water partition coefficient) are also commonly used to describe the extent of sorption. K0M is often estimated as 0.56 KoC, implying that organic matter is 56% carbon. 

From the data given, DDT, a toxic pesticide now banned in the United States, is not very soluble in water, but is soluble in fat and fatty tissue. Therefore, it probably is not ionic, so therefore it does not have ion-ion interactions. It probably does not have hydrogen bonding in operation to any extent, because it is not very soluble in water, but is soluble in fat. So, most likely DDT has only dipole-dipole and dispersion forces in operation between its molecules. 

Historically, organic environmental pollutants were hydrophobic, often persistent, neutral compounds. As a consequence, these substances were readily sorbed by particles and soluble in lipids. In modern times, efforts have been made to make xenobiotics more hydrophilic - often by including ionisable substituents. Presumably, these functional groups would render the compound less bioaccumulative. In particular, many pesticides and pharmaceuticals contain acidic or basic functions. However, studies on the fate and effect of organic environmental pollutants focus mainly on the neutral species [1], In the past, uptake into cells and sorption to biological membranes were often assumed to be only dependent on the neutral species. More recent studies that are reviewed in this chapter show that the ionic organic species play a role both for toxic effects and sorption of compounds to membranes. 

Phosphorescence can also be detected when the phosphor is incorporated into an ionic micelle. Deoxygenation is still required either by degassing with nitrogen or by the addition of sodium sulphite. Micellestabilized room-temperature phosphorescence (MS RTP) promises to be a useful analytical tool for determining a wide variety of compounds such as pesticides and polyaromatic hydrocarbons. 

A possible source of groundwater contamination, which has up to now almost been neglected, is associated with the introduction of surfactants into soils as pesticide additives (Table 6.7.3). Non-ionic surfactants composed of alcohols and fatty acids are most widely recommended as adjuvants to facilitate and enhance the absorbing, emulsifying, dispersing, wetting and penetrating properties of pesticides. Other pesticide adjuvants are silicone-based surfactants,... 

With the exception of picloram and phenols (Fig. 10, Table 3), acidic pesticides are considered nonvolatile from aqueous and soil systems [153]. Some ester formulations of these compounds also behave as herbicides. They do not ionize in solution and are less water-soluble than the acid or salt forms. They are eventually hydrolyzed to acid anions in aqueous and soil systems, but in the ester form are non-ionic and relatively volatile. 

Amitrole (i. e., a weakly basic pesticide) and the insecticide Dimefox (tetra-methyl phosphorodiamidic fluoride) have been shown to be adsorbed by HA through ionic bonding [17, 151-153]. The interaction between the cationic pesticide Chlorodimeform and SPHA was studied and, based on IR data, Maqueda et al. [154] indicated that an ion exchange bonding mechanism occurred. 

A water soluble liquid formulation (WSL) is prepared from pesticides that are highly water soluble. This is, by far, the simplest type of formulation. One distinct advantage of WSL s over other formulations is that the field spray dilutions are infinitely stable as true solutions. Pesticides that are hydrophilic and ionic, such as inorganic or organic metallic salts, often fall into this category. Unfortunately, only a small portion of all pesticides are adequately soluble in water. 

The amount of adsorbed chemical is controlled by both properties of the chemical and of the clay material. The clay saturating cation is a major factor affecting the adsorption of the organophosphorus pesticide. The adsorption isotherm of parathion from an aqueous solution onto montmorillonite saturated with various cations (Fig. 8.32), shows that the sorption sequence (Al > Na > Ca ) is not in agreement with any of the ionic series based on ionic properties. This shows that, in parathion-montmoriUonite interactions in aqueous suspension, such factors as clay dispersion, steric effects, and hydration shells are dominant in the sorption process. In general, organophosphorus adsorption on clays is described by the Freundhch equation, and the values for parathion sorption are 3 for Ca +-kaoUnite, 125 for Ca -montmorillonite, and 145 for Ca -attapulgite. 

Many pesticides degrade to polar products that form organic anions in a water matrix. These are sometimes missed due to the difficulty in extracting trace amounts of the ionic material from a water matrix. A recently developed anion exchange procedure for isolating acidic compounds from dilute aqueous solutions (10-12) was used for recovering the anionic material from liquid samples collected from the two pits. 

In order to more closely represent the volatilization environment that would be encountered in an evaporation pond, Triton X-100, a non-ionic emulsifier similar to those used in some pesticide formulations, was added to prepared pesticide solutions at 1000 ppm. The presence of this emulsifier caused a decrease in the percent pesticide volatilized in one day in all cases except for mevinphos (Table VI). Three mechanisms are probably in operation here. First, Triton X-100 micelles will exist in solution because its concentration of 1000 ppm is well above its critical micelle concentration of 194 ppm (30). Pesticide may partition into these micelles, reducing the free concentration in water available for volatilization, which will in turn reduce the Henry s law constant for the chemical (31). Second, the pesticides may exhibit an affinity for the thin film of Triton that exists on the water surface. One can no longer assume that equilibrium exists across the air-water interface, and a Triton X-100 surface film resistance... 

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