Pesticide separation

So far, capillary electrochromatography has found only a few applications to pesticides. Separation of cinosulfiiron and its by-products can serve as a good example. The separation was done with a C-8 non-endcapped 3 pm packing in a capillary whose dimensions were 33.5 cm (25.0 cm to the detector) x 100 pm internal diameter. A typical separation is presented in Fig. 10.27 [128],... 

Pesticides Separated on a CN-Bonded Polar Phase. Figures 3 and 4 contain the chromatograms obtained for several of the pesticides listed in Table 2. Various mobile phases were used to facilitate separation on the CN-bonded polar phase. Detection is shown in both absorbance and fluorescence modes. It would appear that fluorescence detection is more sensitive for some pesticides, while absorbance detection is more sensitive for others. However, comparisons of one manufacturer s absorbance monitor with another manufacturer s fluorescence monitor could be misleading. (I will refer to this under Instrumental Parameters.) Furthermore, the ultimate useful comparison is obtained when practical samples are chromatographed since these... 

For analyzing water pollution it is necessary to know the area where the sample(s) were harvested. Among the primary water pollutants are pesticides, since they are slowly degraded and require dissemination. The chlorinated pesticides are lipophilic and are slowly accumulated in animals. The effect is due to metabolic system perturbation. Other water pollution sources are heavy metals, which are determined by the highly sensitive and selective analytical method ICP-AES.29 The sampling process, in this case, consists of chromatographic separation techniques for pesticide separation.30... 

Both electron impact (El) and chemical ionization (Cl) are currently used as ionization techniques in MSD, in addition to the positive or negative ion monitoring modes. The use of the selective ion monitoring (SIM) feature improves the sensitivity greatly, although some structural confirmation is lost. In Table 8, the ion fragments frequently monitored in MSD for some pesticides separated by GC are listed. 

Table 8 Major m/e signals in the mass spectra of some pesticides separated in gas chromatography with mass spectrometric detection (ionization by electron impact) ...

For pesticide separations by LC, different calibration approaches were studied. Among external solvent solubilized standard , internal standard , external matrix-matched standard , and echo peak internal standard approaches, the last two procedures generate better results. The echo peak internal standard is a novel technique based on the possibility of producing a delayed injection of an internal standard having the same identity as the target compound. 

Because GC is excellent for quantitative analysis, it has found wide use for many different applications. Sensitive, quantitative detectors provide fast, accurate analyses, and at a relatively low cost. A pesticide separation illustrating the high speed, sensitivity, and selectivity of GC is shown in Figure 1.7. 

Example chromatograms of the common organochlorine pesticides separated by these conditions are shown in Figure 15.19. The chromatograms are generated from a continuous calibration standard in hexane with each pesticide in the range of 10-20 ng/mL. The surrogate standards, tetrachloro-meto-xylene (TCX) and decachlorobiphenyl (DCB), are present at approximately 40 ppb. 

Two examples from the analysis of water samples illustrate how a separation and preconcentration can be accomplished simultaneously. In the gas chromatographic analysis for organophosphorous pesticides in environmental waters, the analytes in a 1000-mL sample may be separated from their aqueous matrix by a solid-phase extraction using 15 mb of ethyl acetate. After the extraction, the analytes are present in the ethyl acetate at a concentration that is 67 times greater than that in... 

This publication provides several examples of the use of solid-phase extractions for separating analytes from their matrices. Some of the examples included are caffeine from coffee, polyaromatic hydrocarbons from water, parabens from cosmetics, chlorinated pesticides from water, and steroids from hydrocortisone creams. Extracted analytes maybe determined quantitatively by gas (GC) or liquid chromatography (LG). 

A chromatographic analysis for the chlorinated pesticide Dieldrin gives a peak with a retention time of 8.68 min and a baseline width of 0.29 min. How many theoretical plates are involved in this separation Given that the column used in this analysis is 2.0 meters long, what is the height of a theoretical plate ... 

The value of many chemical products, from pesticides to pharmaceuticals to high performance polymers, is based on unique properties of a particular isomer from which the product is ultimately derived. Eor example, trisubstituted aromatics may have as many as 10 possible geometric isomers whose ratio ia the mixture is determined by equiHbrium. Often the purity requirement for the desired product iacludes an upper limit on the content of one or more of the other isomers. This separation problem is a compHcated one, but one ia which adsorptive separation processes offer the greatest chances for success. 

Sprays. Aerosol spray emulsions are of the water-in-oil type. The preferred propellant is a hydrocarbon or mixed hydrocarbon—hydrofluorocarbon. About 25 to 30% propellent, miscible with the oil, remains in the external phase of the emulsion. When this system is dispensed, the propellant vaporizes, leaving behind droplets of the w/o emulsion (Fig. 2b). A vapor tap valve, which tends to produce finely dispersed particles, is employed. Because the propellant and the product concentrate tend to separate on standing, products formulated using this system, such as pesticides and room deodorants, must be shaken before use. 

MIBK is a highly effective separating agent for metals from solutions of their salts and is used in the mining industries to extract plutonium from uranium, niobium from tantalum, and zirconium from hafnium (112,113). MIBK is also used in the production of specialty surfactants for inks (qv), paints, and pesticide formulations, examples of which are 2,4,7,9-tetramethyl-5-decyn-4,7-diol and its ethoxylated adduct. Other appHcations include as a solvent for adhesives and wax/oil separation (114), in leather (qv) finishing, textile coating, and as a denaturant for ethanol formulations. 

Methyl- and dimethylnaphthalenes are contained in coke-oven tar and in certain petroleum fractions in significant amounts. A typical high temperature coke-oven coal tar, for example, contains ca 3 wt % of combined methyl- and dimethylnaphthalenes (6). In the United States, separation of individual isomers is seldom attempted instead a methylnaphtha1 ene-rich fraction is produced for commercial purposes. Such mixtures are used for solvents for pesticides, sulfur, and various aromatic compounds. They also can be used as low freezing, stable heat-transfer fluids. Mixtures that are rich in monomethyinaphthalene content have been used as dye carriers (qv) for color intensification in the dyeing of synthetic fibers, eg, polyester. They also are used as the feedstock to make naphthalene in dealkylation processes. PhthaUc anhydride also can be made from m ethyl n aph th al en e mixtures by an oxidation process that is similar to that used for naphthalene. 

Field studies are required to provide a more reaUstic picture of the dissipation of the parent compound and those degradates determined to be significant. Under field conditions pesticides are exposed simultaneously to the individual dissipation processes that were examined separately in the laboratory studies. Thus, in field studies, some dissipation processes may be altered due to competition and interaction. Requirements for spray drift data were outlined in draft Subdivision R, but the EPA agreed that data generated on a generic basis by an industry consortium could represent the potential for drifting of individual pesticides. 

Sorption and Desorption Processes. Sorption is a generalized term that refers to surface-induced removal of the pesticide from solution it is the attraction and accumulation of pesticide at the sod—water or sod—air interface, resulting in molecular layers on the surface of sod particles. Experimentally, sorption is characterized by the loss of pesticide from the sod solution, making it almost impossible to distinguish between sorption in which molecular layers form on sod particle surfaces, precipitation in which either a separate soHd phase forms on soHd surfaces, covalent bonding with the sod particle surface, or absorption into sod particles or organisms. Sorption is generally considered a reversible equdibrium process. 

Uses. Tballium compounds have limited use in industrial appHcations. The use of thaHous sulfate in rodenticides and insecticides has been replaced by other compounds less harmful to animals (see Insect control technology Pesticides). Tb allium sulfide has been used in photoelectric cells (see Photovoltaic cells). A thallium bromide—thallium iodide mixture is used to transmit infrared radiation for signal systems. ThaHous oxide is used in the manufacture of glass (qv) that has a high coefficient of refraction. Tb allium formate—malonate aqueous solutions (Cletici s solution) have been used in mineral separations. Many thallium compounds have been used as reagents in organic synthesis in researchlaboratoti.es. 

A multiresidue analytical method based on sohd-phase extraction enrichment combined with ce has been reported to isolate, recover, and quantitate three sulfonylurea herbicides (chlorsulfuron, chlorimuron, and metasulfuron) from soil samples (105). Optimi2ation for ce separation was achieved using an overlapping resolution map scheme. The recovery of each herbicide was >80% and the limit of detection was 10 ppb (see Soil chemistry of pesticides). 

We can list the following areas as prime targets essential oil and natural product analysis, chiral analysis (e.g. of fragrances), trace multi-residue analysis, pesticide monitoring, and further petroleum products applications, in fact any separation where simply greater resolution and sensitivity is demanded-which means probably almost... 

Z. Liu, S. R. Siiimanne, D. G. Patterson-Jr, L. L. Needham and J. B. Phillips, Comprehensive two-dimensional gas cliromatography for the fast separation and determination of pesticides exrtacted from human serum . Anal. Chem. 66 3086-3092 (1994). 

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Figure 10.14 Schematic representation of the SFSPE/SFC set-up developed by Murugaverl and Vooi hees (67). Reprinted from Journal of Microcolumn Separation, 3, B. Mumgaverl and K. J. Vooi hees, On-line supercritical fluid exti aaion/chromatography system for ti ace analysis of pesticides in soybean oil and rendered fats , pp. 11-16, 1991, with permission from John Wiley and Sons, Inc.

Today, however, GC-GC coupling is seldom used to determine pesticides in environmental samples (2), although comprehensive MDGC has been applied to determine pesticides in more complex samples, such as human serum (19). On the other-hand, new trends in the pesticide market, which is now moving towards the production of optically active enantiomers and away from racemic mixtures, may make this area suitable for GC-GC application. The coupling of non-chiral columns to chiral columns appears to be a suitable solution to the separation problems that such a trend might cause. 

---