Chlorinated acid herbicides

A method that uses high performance liquid chromatography/ mass spectrometry (HPLC/MS) for the analysis of chlorinated phenoxyacid herbicides is described. During method development different techniques were used to increase both the sensitivity and the specificity of thermospray HPLC/MS for chlorinated acid herbicides. These included the operation of the instrument in the negative chemical ionization (NCI) mode initiated by discharge and the use of a wire-repeller in the ion source for efficient extraction of positive ions. Single quadrupole repeller-induced and multiple quadrupole collision activated dissociation (CAD) experiments were also performed to increase the structural information of the mass spectra. 

This method complements the U.S. Environmental Protection Agency s gas chromatographic (GC) SW-846 Method 8151 for the determination of chlorinated acid herbicides. Method 8151 prescribes the use of hydrolysis to ensure that these compounds arc in the acid form, reaction of the acids with diazomethane to produce methyl esters, and GC or GC/MS analysis. This HPLC method eliminates the need for most sample preparation steps and allows direct analysis of sample extracts. 

TABLE I. Positive Ion Buffer Assisted Ion Evaporation Mass Spectra of Chlorinated Acid Herbicides... 

In many contributions reporting on acidic pesticides in environmental samples ESI applied as ion spray was predominantly performed to analyse these pollutants. APCl, however, was not as effective as ESI as studies with standard solutions of the pesticide mixtures made obvious [325] when phenoxy acid compounds were determined using both types of interface. MSn quantitative results were used for confirmation. Mass detection after CZE-MS interfaced by ESI was successfully apphed to analyse drinking water spiked with chlorinated acid herbicides. Selected-ion elec-... 

X. Song and W.L. Budde, Determination of chlorinated acid herbicides and related compounds in water by capillary electrophoresis-electrospray negative ion mass spectrometry, J. Chromatogr. A, 829, 327-340, 1998. 

Certain organic compounds are too polar and nonvolatile for gas chromatographic analysis. The chlorinated acid herbicides fall into this category. Included in this... 

DETERMINATION OF NONVOLATILE COMPOUNDS AND CHLORINATED ACID HERBICIDES... 

Another case of high nitrosamine concentration in chlorinated phenoxy- and benzoic acid herbicides was resolved by the elimination by the manufacturer of nitrite salts in the formu-... 

Haugland RA, DJ Schlemm, RP Lyons, PR Sferra, AM Chakrabarty (1990) Degradation of the chlorinated phenoxyacetate herbicides 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid by pure and mixed bacterial cultures. Appl Environ Microbiol 56 1357-1362. 

Renberg [35] used an ion-exchange technique for the determination of chlorophenols and phenoxy acetic acid herbicides in soil. In this method the soil extracts are mixed with Sephadex QAE A-25 anion exchanger and the adsorbed materials are then eluted with a suitable solvent. The chlorinated phenols are converted into their methyl ethers and the chlorinated phenoxy acids into their methyl or 2-chloroethyl esters for gas chromatography. 

Chlorinated phenoxypropanoic acid herbicides have been very widely used following the introduction of products such as Dalapon in the 1950s. More recently Mecoprop and... 

Chlorinated [407,408] and 2,4-dinitrophenoxy acid herbicides [409] have been determined. liquid chromatography particle beam mass spectrometry has been used as an analytical finish [408]. Crescenzi et al. [410] evaluated the feasibility of selectively and rapidly extracting herbicide residues in soils by hot water and collecting analytes with a Carbograph 4 solid-phase extraction cartridge set on-line with the extraction cell. Phenoxy acid herbicides and those non-acidic and acidic herbicides that are often used in combination with phenoxy acids were selected for this study. Five soil samples were... 

Table 6.4 shows first-order rate coefficients and tx/2 values for degradation of a number of pesticides in soils (Rao and Davidson, 1982). The k and t1/2 values calculated from field data are based on the disappearance of the parent compound (solvent extractable). Table 6.4 also includes k and t1/2 values calculated on mineralization (14C02 evolution) and parent-compound disappearance from laboratory studies. The t1/2 values were smaller for field than for laboratory studies. Rao and Davidson (1980) attribute this to the multitude of factors that can affect pesticide disappearance in the field while only one factor is studied in the laboratory. Rao and Davidson (1982) suggested that pesticides be classified into three groups based on values (Table 6.5) nonpersistent (t1/2 < 20 days), moderately persistent (20 < t1/2 < 100 days), and persistent (/1/2 > 100 days). Most chlorinated hydrocarbons are grouped as persistent, while carboxyl-kanoic acid herbicides are nonpersistent. The s-triazines, substituted ureas, and carbamate pesticides are moderately persistent. 

Lindane is relatively non-persistent, especially under anaerobic conditions, and although its more highly chlorinated residues may present the same problems as those of polychlorophenols, the less chlorinated residues should follow pathways similar to those established for the microbial degradation of the chlorinated phenoxyalkanoic acid herbicides. Recent evidence (46) indicates that certain microbes can dechlorinate DDT anaerobically, thereby making available intermediates which may undergo further aerobic attack, leading in principle to total degradation. The ultimate fate of the hexachloronorbornene nucleus of cyclodienes is still uncertain and this question continues to attract attention. 

An early chlorinated phenoxy acid herbicide (2,4-D) was first discovered in 1932. Although this compound rapidly breaks down in the environment, the seed fungicide hexachlorobenzene (HCB), introduced in 1933, was found to be far more persistent.2 The structurally similar insecticide hexachlorocyclohexane or... 

In relation to this article, those chlorinated pesticides which are rapidly degraded in the environment, and considered as non-persistent, will not be discussed. Compounds such as atrazine, chlorpyrifos and the phenoxy acid herbicides (2,4-D), mecoprop, MCPA, etc.) all contain organic chlorine and may... 

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