Pesticides and related compounds

Although fluorimetric analysis has been in use for a number of years in biochemistry, biology and related areas, it has had only limited use for pesticide residues and has been restricted to those compounds which exhibit a sufficiently strong intrinsic fluorescence. 

The initial studies on fluorimetry of pesticides were made in solution. The fluorescence behaviour of compounds such as Guthion (azinphosmethyl), Potsan, Warfarin and piperonyl butoxide was investigated for possible uses in the analysis of their residues [145]. Much work has been done by Sawicki and his co-workers in connection with fluorescent air pollutants and this has recently been reviewed [146]. However, most of the fluorimetric analyses of pesticides require pre-treatment of the compounds in order to convert them into fluorescent species. 

Most of the older methods of fluorimetric analysis of pesticides involved hydrolysis to form fluorescent anions. Co-ral (coumaphos) [147] was hydrolyzed in alkali to the hydroxybenzopyran, which was subsequently determined by means of its fluorescence. Guthion (azinphosmethyl) was hydrolyzed to anthranilic acid for fluorimetric analysis [148,149]. A method was developed [150] for Maretin (N-hydroxynaphthalimide diethyl phosphate) in fat and meat which involved hydrolysis in 0.5 M methanolic sodium hydroxide followed by determination of the fluorescence of the liberated naphthalimide moiety. Carbaryl (1-naphthyl N-methylcarbamate) and its metabolites have been determined by a number of workers using base hydrolysis and the fluorescence of the resulting naphtholate anion [151-153]. Nanogram quantities of the naphtholate anion could be detected. Zectran (4-dimethylamino-3,5-xylyl N-methylcarbamate) has been determined by the fluorescence of its hydrolysis product [154]. The fluorescence behaviour of other carbamate insecticides in neutral and basic media has been reported [155]. Gibberellin spray used on cherries has been determined fluorimetrically after treatment with strong acid [156]. Benomyl (methyl N-[l-(butylcarbamoyl)-2-benzimidazolyl]carbamate) has been analyzed by fluorimetry after hydrolysis to 2-aminobenzimidazole [157]. 

The use of chromatography with the above techniques has not yet been reported, but could prove to be very useful since the hydrolysis products could be chromatographed in a suitable system and detected directly under suitable conditions (either TLC or HPLC). 

The use of pH-sensitive fluorescent indicators as spray reagents has been recently examined for the determination of sulphur-containing pesticides and amino acids separated by TLC [158,159]. The procedure is adapted from a ligand-exchange method of Frei and Mallet [160]. The separated pesticides are brominated directly on the TLC plate. This treatment oxidizes the pesticides and liberates hydrobromic acid as a side product. On 

Chlorophenols, such as 2,4-dichlorophenol, occur as impurities in chlorophenoxy herbicide formulations at concentrations of about 1% (w/w) of the herbicides. Akerblom and Lindgren used serial UV (280 nm) and ED (carbon paste electrode, + 1.05 V vs Ag/AgCl) for the herbicides and chlorophenols, respectively. The analytical column was ODS-modified silica and the eluent was methanol-aq. acetic acid (0.1 mol L ) (9 + 11 to 11 + 9 depending on the formulation under analysis). This approach could prove useful for the analysis of these compounds in biological specimens. 

ODS-based columns and eluents of pH 2.5-6.0 were evaluated. Detection was at a GCE (+1.25 V V5 Ag/AgCl). 

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Hall GL, Whitehead WE, Mourer CR, et al. 1986. A new gas chromatographic retention index for pesticides and related compounds. J High Resolut Chromatogr Commun 9 266-271. 

There are a large number of literature references that refer the use of SPE cartridges for the extraction of pesticides from water. There are several comprehensive reviews of the use of SPE, including that by Soriano et al. who discussed the advantages and limitations of a number of sorbents for the analysis of carbamates. Hennion reviewed the properties and uses of carbon based materials for extraction of a wide multiclass range of pesticides. Thorstensen et al. described the use of a high-capacity cross-linked polystyrene-based polymer for the SPE of phenoxy acids and bentazone, and Tanabe et al reported the use of a styrene-divinylbenzene copolymer for the determination of 90 pesticides and related compounds in river water. SPE cartridges are also widely used for the cleanup of solvent extracts, as described below. 

Organochlorine pesticides and related compounds Use Detected residues mcg/kg)... 

Haggblom, M. M. (1992). Microbial breakdown of halogenated aromatic pesticides and related compounds. FEMS Microbiology Reviews, 103, 29-72. 

Y Pico, JC Molto, J Manes, G Font. Solid phase techniques in the extraction of pesticides and related compounds from foods and soil. J Microcol Sep 6 331-359, 1994. 

Tanabe, A. and K. Kawata (2004). Determination of triazine pesticides and related compounds in environmental water by liquid chromatography-mass spectrometry. Analyt. Sci., 20 227-230. 

THE ORGANOHALOGEN AROMATIC AND CYCLIC PESTICIDES AND RELATED COMPOUNDS... 

Manual for Analytical Quality Control for Pesticides and Related Compounds in Human and Environmental Samples. U.S. Environmental Protection Agency. Health Effects Research Laboratory. Research Triangle Park, North Carolina. 

If present trends toward increased use of pesticides and related compounds continue, it is quite possible that quantities of these materials... 

Table IV. Absorption Maxima of Some Chlorinated Hydrocarbon Pesticides and Related Compounds...

Most applications of DLI LC-MS deal with qualitative analysis, where in most cases only molecular-mass information is obtained. DLI LC-MS found extensive apphcation in the analysis of pesticides and related compounds [35], in the quahtative and quantitative determination of corticosteroids and metabolites in equine urine [36]. Highly labile compounds such as vitamin B12 (molecular weight 1354) and erythromycin A (molecular weight 733) were analysed by DLI negative-ion Cl LC-MS [33]. As an example, the negative-ion Cl spectram of 92 ng vitamin B12 is shown in Figure 4.7. 

LC-MS plays an important role in the analysis of pesticides and related componnds, e.g., herbicides, insecticides, acaricides, as well as their degradation prodncts and metabolites. The analysis of pesticides is relevant for environmental studies, food safety, toxicology, and occupational health. Pesticides have to be analysed in environmental samples, such as different water compartments, soil, sediments, sludge, and animal tissue like fish, in food, especially fruit and vegetables, and in (human) body fluids and tissues. Many modem pesticides and related compounds are not amenable to GC-MS analysis, or only after derivatization. Therefore, LC-MS has been evaluated as an alternative. Various review papers on the analysis of pesticides and related compounds in various sample matrices were published [1-8]. 

This chapter is devoted to the analysis of pesticides and related compounds. LC-MS characteristics of various classes of pesticides are described, i.e., the mass spectral information obtained using electrospray ionization (ESI) and atmospheric-pressure chemical ionization (APCI). Next, typical strategies with the analysis of pesticides in environmental samples and in fmit and vegetables are discussed. 

Many papers on the LC-MS analysis of pesticides and related compounds deal with the characterization of interface and ionization performance, the improvement of detection limits by variation of experimental conditions, and the information content of the mass spectra. As far as ESI and APCI ate concerned, this type of information is reviewed for various pesticide classes in this section (see Ch. 4.7.4 for results with thermospray and Ch. 5.6.1 with particle-beam interfacing). 

Tamura H, Yoshikawa H, Gaido KW, Ross SM, DeLisle RK, Welsh WJ, Richard AM. Interaction of organophosphate pesticides and related compounds with the androgen receptor. Environ Health Perspect 2003 111 545-52. 

For a good discussion of on-line SPE coupled to HPLC, the work of Hennion and Pichon (1994) and Hennion and co-workers (1990) discuss environmental applications. In their work, the styrene-divinylbenzene copolymers are used as SPE columns with good capacity for many of the environmentally relevant contaminants and allow for direct analysis by HPLC. Hennion and Pichon (1994) discuss and review a number of studies on pesticides and related compounds by on-line SPE. There is also more discussion of on-line SPE methods coupled to GC/MS in Chapter 10. 

Slobodnik, J., B.L.M. van Baar, and U.A.Th. Brinkman. 1995. Column liquid chromatography-mass spectrometry seleded techniques in environmental applications for polar pesticides and related compounds. J. Chromatogr. A 703 81-121. 

Rathore, H. S. and Begum, T., Thin-layer chromatographic behavior of carbamate pesticides and related compounds, J. Chromatogr., 643, 321-329, 1993. 

Depending on the duration, frequency, and level of exposure, anti-AChE pesticides and related compounds can adversely affect one or all three components of the matemal-placental-fetal unit, The outcome of placental toxicity to these pesticides can be Influenced by three major factors maternal toxicity, placental tran.sfer, and placentai-fetal metabolism. Evidence suggests that the pesticide residue is present not only in the exposed mother... 

Kupfer, D. (1967). Effects of some pesticides and related compound. on steroid function and metabolism. Residue Rev. 19, 11-30. 

Figure 7.4 Some pesticides and related compounds measured by HPLC-ED (MHBC — methyl 5-hydroxy-2-benzimidazole carbamate, glufosinate is the ammonium salt of phosphinothricin).

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