Chlorophenoxy acids

Chlorophenoxy acids are relatively polar pesticides which are usually determined by LC because volatile derivatives have to be prepared for GC analysis. This group of herbicides can be detected by multiresidue methods combined with automated procedures for sample clean-up, although selectivity and sensitivity can be enhanced by coupled-column chromatographic techniques (52). The experimental conditions for Such analyses are shown in Table 13.1. 

Figure 13.11 Column-switcliing RPLC trace of a surface water sample spiked with eight chlorophenoxyacid herbicides at the 0.5 p-g 1 level 1, 2,4-dichlorophenoxyacetic acid 2, 4-chloro-2-methylphenoxyacetic acid 3, 2-(2,4-diclilorophenoxy) propanoic acid 4, 2-(4-cliloro-2-methylphenoxy) propanoic acid 5, 2,4,5-trichlorophenoxyacetic acid 6, 4-(2,4-dichlorophenoxy) butanoic acid 7, 4-(4-chloro-2-methylphenoxy) butanoic acid 8, 2-(2,4,5-tiichlorophenoxy) propionic acid. Reprinted from Analytica Chimica Acta, 283, J. V. Sancho-Llopis et al., Rapid method for the determination of eight chlorophenoxy acid residues in environmental water samples using off-line solid-phase extraction and on-line selective precolumn switcliing , pp. 287-296, copyright 1993, with permission from Elsevier Science.

Chlorophenols, manufacture of, 23 654 Chlorophenoxy acid herbicides, 73 304 (E) -(RS) -1 -(4-Chlorophenyl) -4,4-dimethyl-2-(lH- l,2,4-triazol-l-yl)-pent-l-en-3-ol, 73 47—48. See also 4-Chlorophenyl-4,4- dimethyltriazol pentenol 4-Chlorophenyl-4,4-dimethyltriazol pentenol, 73 40t, 47 48 Chlorophosphazenes, 19 55, 56 in silicone polymerization, 22 556... 

HMSO (1986) Chlorophenoxy acid herbicides, trichlorobenzoic acid, chlorophenols, triazines and glyphosate in water. HMSO, London... 

Gomez, ]., Bruneau, C., Soyer, N., and Brault, A. Thermal degradation of chlorophenoxy acid herbicides. J. Agric. Food Chem., 36(3) 649-653, 1988. 

Uses. Intermediate in production of her-bicidal chlorophenoxy acids such as 2,4-dichlorophenoxyacetic acid... 

Yu, L., Qin, W., and Li, S. F. Y, Ionic liquids as additives for separation of benzoic acid and chlorophenoxy acid herbicides by capillary electrophoresis. Anal. Chim. Acta, 547,165-171,2005. 

Methods for Organochlorine Pesticides and Chlorophenoxy Acid Herbicides in Drinking Water and Raw Source Water Environmental Monitoring and Support Laboratory. U.S. Environmental Protection Agency Cincinnati, OH EPA 600/4-81-053. 

J. V. Sancho-Llopis, F. Hernandez-Hernandez, E. A. Hogendoorn and P. van Zoonen, Rapid method for the determination of eight chlorophenoxy acid residues in environmental water samples using off-line solid-phase extraction and on-line selective precolumn switching , Anal. Chim. Acta 283 287-296(1993). 

Some Common Chlorophenoxy Acid Herbicides Table 2.13.1... 

This is applied to separate acidic or basic organics from neutral organics. The solvent extract is shaken with water that is highly basic. The acidic organics partition into the aqueous layer whereas, the basic and neutral compounds stay in the organic solvent and separate out. After this, the aqueous layer is acidified to a pH below 2, and then extracted with methylene chloride. The organic layer now contains the acid fraction Phenols, chlorophenoxy acid, herbicides, and semivolatile organic pollutants are cleaned up by the procedure described above. 

Chlorophenoxy acid 2,4-D, silvex Sample acidified with H3P04, analytes... 

Chlorophenoxy acids are one of the most important classes of chlorinated herbicides. In these compounds, chlorosubstituted benzene rings are attached to lower carboxylic acids via an oxygen atom, as shown in the following structures ... 

Some of the common chlorophenoxy acid herbicides are listed in Table 2.11.1. 

Aqueous samples are extracted with diethyl ether while soils, sediment, and solid wastes are extracted with acetone and diethyl ether. Prior to extraction, the sample is acidified with HC1 to a pH below 2. Such acidification is necessary due to the fact that in nature or in the environmental matrix, herbicides may occur as acids, salts, or esters. Acidification converts all these forms into chlorophenoxy acids. 

The potassium salts of the herbicides are then converted back to their acids by treatment withH2S04. The aqueous solution is acidified with cold 1 3 H2S04 to pH below 2. The chlorophenoxy acids regenerated are then extracted into ether in a separatory funnel by repeat extractions. The aqueous phase is discarded in order to achieve complete esterification of herbicide acids. The ether extract containing herbicides must be completely free from moisture even at trace level. Therefore, add acidified anhydrous Na2S04 to the extract in excess... 

Chlorophenoxy acids after being extracted out from the sample matrix, separated from organic interferences and concentrated down into a small volume of ether, are now converted into their methyl esters. Such esterification of herbicides is essential for their determination by GC. While chlorophenoxy acids themselves show poor response, their ester derivatives produce sharp peaks with good resolution. 

Packed column 1.8 m x 4 mm ID glass packed with either (1) 1.5% SP 2250/1.95% SP-2401 on Supelcoport (100/120 mesh) (2) 5% OV-210 on Gas Chrom Q (100/120 mesh) or (3) 1.5% OV-17/1.95% QF-1. Efficient separation can also be achieved on a 2 mm ID column. Use 5% argon-95% methane carrier gas at flow rate of 60 to 70 niL/rnin when using a 4 mm ID column while for a 2 mm ID column the carrier gas flow rate should be 20 to 30 mL/min. An oven temperature isothermal between 160° and 190°C should be suitable. Under the above conditions of temperature and carrier gas flow rate, most chlorophenoxy acid methyl esters elute within 10 min on a 4 mm ID packed column. 

The methyl esters can be also determined by GC-FID. Using a 30 m x 0.32 mm ID x 0.25 pm (film thickness) capillary column, such as DB-1701 or equivalent, the compounds can be adequately separated and detected by FID. The recommended carrier gas (helium) flow rate is 35 cm/s, while that of the makeup gas (nitrogen) is 30 cm/min. All of the listed herbicides may be analyzed within 25 min. The oven temperature is programmed between 50 and 260°C, while the detector and injector temperatures should be 300 and 250°C, respectively. The herbicides may alternatively converted into their trimethylsilyl esters and analyzed by GC-FID under the same conditions. FID, however, gives a lower response as compared with ECD. The detection level ranges from 50 to 100 ng. For quantitation, either the external standard or the internal standard method may be applied. Any chlorinated compound stable under the above analytical conditions, which produces a sharp peak in the same RT range without coeluting with any analyte, may be used as an internal standard for GC-ECD analysis. U.S. EPA Method 8151 refers the use of 4,4,-dibromooctafluorobiphenyl and 1,4-dichlorobenzene as internal standards. The quantitation results are expressed as acid equivalent of esters. If pure chlorophenoxy acid neat compounds are esterified and used for calibration, the results would determine the actual concentrations of herbicides in the sample. Alternatively, if required, the herbicide acids can be stoichiometrically calculated as follows from the concentration of their methyl esters determined in the analysis ... 

The molecular weights of herbicide acids are presented under individual compounds listed alphabetically in Part 3. To determine the molecular weights of the respective methyl esters, add 14 to the molecular weights of the corresponding chlorophenoxy acids. 

Analysis for 2,4-D and 2,4,5-T in the air may be performed using NIOSH Method 5001. Other chlorophenoxy acid herbicides such as 2,4,5-TP, 2,4-DB, and MCPA can be analyzed in a same general way. The method involves HPLC determination of herbicides in the form of acids or salts but not their esters. 

Between 20 and 200 L air at a flow rate of 1 to 3 L/min is passed through a glass fiber filter. The herbicides and their salts, deposited on the filter, are desorbed with methanol, and the chlorophenoxy acid anions are determined by HPLC using UV detector at 284 to 289 nm. The LC eluent is a mixture of NaC104-Na2B407 at 0.001 M concentration. Other eluent composition and UV detector wavelength may be used. A stainless steel column 50 cm x 2 mm ID, packed with Zipax Sax or equivalent may be used at ambient temperature and 1000 psi. 

Sherma, J (1986). Determination of triazine and chlorophenoxy acid herbicides in natural water samples by solid phase extraction and quantitative thin layer chromatography. J. Liquid Chromatog., 9(16) 3433-3438. 

Fletcher, C.A., N.C. Meakins, J.M. Bubb, and J.N. Lester (1994). Magnitude and distribution of contaminants in salt marsh sediments of the Essex coast, UK. III. chlorophenoxy acid and. v-lriazinc herbicides. Sci. Tot. Environ., 155 61-72. 

The chlorophenoxy acids, salts and esters are moderately irritating to eyes, skin, respiratory tract and lining of the GI tract. Prolonged and/or repeated dermal contact may result in depigmentation. 

In humans, the ingestion of large amounts of the chlorophenoxy acids ... 

Chlorophenoxy acid herbicides are also widely used to control broadleaf weeds and grass plants. Several immunoassays have been reported for 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).246 247 Several immunosensors have been described using a transducing principle similar to the RIANA system already described in this chapter. Thus, Meusel et al.248 reported the use of monoclonal antibodies in a sensor chip to analyze river and lake water samples, obtaining detection limits of 0.1 ig L 1. Moreover, monoclonal antibodies, produced by Cuong et al.,249 were used in a dipstick immunoassay format to analyze pond water samples. When applied to the 2,4-D compound, this semiquantitative method yielded for an IC50 of 6 ug I. and an LOD of 0.5 pg L-1. 

Occupational Exposure. Exposures to 2,3,7,8-TCDD, one of the most potent of the CDD congeners, have occurred occupationally in workers involved in the manufacture and application of trichlorophenols and the chlorophenoxy acid herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichloro-phenoxyacetic acid (2,4,5-T). Holmstedt (1980) has reviewed the history of industrial exposures that have occurred between 1949 and 1976, and Kogevinas et al. (1997) summarized recent data on these cohorts. 

Bro-Rasmussen F, Lokke H. 1984. Ecoepidemiology a casuistic discipline describing ecological disturbances and damages in relation to their specific causes exemplified by chlorinated phenols and chlorophenoxy acids. Reg Toxicol Pharmacol 4 391-399. 

In both these areas, chemical derivatisation has traditionally played a role and with the advent of gas chromatography an even more important role. The reasons for preparing a derivative suitable for GC analysis are many and varied and have been discussed thoroughly in a number of books and reviews (l- >). For convenience they are summarised in Table I. As can be seen, two different types of chemical derivatisation techniques are mentioned under Item 4 of Criteria, There is the chemical derivatisation of a pesticide as a pre-requisite of the method of analysis, e.g. esterification of the chlorophenoxy acids, as well as derivatisation as a method for confirmation of identity. The former must meet all the requirements associated with a practical, viable analytical procedure while for the latter the emphasis is on speed, ease of operation and reproducibility. 

---