Alachlor sulfonic acid

Limits of detection for each of the six soil metabolites in surface water and ground-water were determined by using an estimate of variability for the 0.25 pgL fortifications from samples analyzed along with hundreds of surface water and groundwater sets during the years 1999-2001. During these years, the estimated LODs were below 0.1 ug for acetochlor sulfonic acid, acetochlor oxanilic acid, alachlor oxanilic acid, metolachlor sulfonic acid, and metolachlor oxanilic acid and about 0.1 igL for alachlor sulfonic acid. If the actual concentration of an analyte is at this detection limit or greater, there is at least a 95% chance of detection. 

LOQs for each of the six soil metabolites in surface water and groundwaters were determined using analytical results (not corrected for background) of samples fortified at the lowest fortification level, 0.25 igL during the analysis in years 1999-2001. The calculated LOQs for acetochlor oxanilic acid, metolachlor sulfonic acid and metolachlor oxanilic acid are below 0.25 ig L. The calculated LOQs for acetochlor sulfonic acid, alachlor sulfonic acid, and alachlor oxanilic acid are below 0.10 igL. If the true concentration of an analyte is at the LQQ or greater, the standard error of individual measured concentration values relative to the true concentration is at most 10%. 

D.S. Aga, E.M. Thurman, and M.L. Pomes, Determination of alachlor and its sulfonic acid metabolite in water by solid-phase extraction and enzyme-linked immunosorbent assay. Anal. Chem. 66, 1495-1499 (1994). 

Methidathion oxon, see Methldathion Methiocarb sulfone, see Methlocarb Methiocarb sulfoxide, see Methiocarb Methionine, see Thiram Methoxyacetaldehyde, see Alachlor Methoxyacetic acid, see 1,4-Dioxane p-Methoxybenzaldehyde, see Methoxychlor p-Methoxybenzoic acid, see Methoxychlor... 

It was of particular interest to determine whether soil metabolites of alachlor would show significant antibody reactivity, since such metabolites might occur in environmental samples for which alachlor ELISA analysis could be used. The two major soil metabolites of alachlor have been identified as the oxanilic (11) and sulfonic acids (12) (IQ). The cross-reactivity of the antibodies for these compounds was found to be 2.5% and 2.3%, respectively (Figure 3). 

Another concept to consider in reversed-phase elution is selective elution. Selective elution consists of using sequential elution solvents to selectively remove several classes of solutes, or using wash solvents to remove impurities that will interfere with the analysis. An example of selective elution is the separation and isolation of herbicides and their metabolites by a reversed-phase C-18 mechanism. Figure 3.5 shows the separation of alachlor, a herbicide, and its sulfonic-acid metabolite. In this method, both compounds are sorbed to the C-18 resin by a reversed-phase mechanism. Even the ionic sulfonic acid is bound to the C-18 bonded phase. The metabolite, whose structure is shown in Figure 3.5, is a surface-active compound and is bound by reversed phase with its ionic functional group solvated by the aqueous phase. The parent compound is eluted with ethyl acetate while the ionic metabolite stays bound to the C-18 resin. Apparently the solubility of the ionic metabolite in ethyl acetate is too low for dissolution. When methanol is applied to the column, the sulfonic acid metabolite elutes from the column. Thus, a fractionation is obtained by selective elution (Aga et al., 1994). 

Figure 3.5. Example of selective elution of alachlor and its sulfonic-acid metabolite with ethyl acetate and methanol.

Sulfonic acids are produced as metabolites of alachlor and meto-lachlor, and the metabolite from metolachlor has been synthesized for FAB-MS comparison with the compound isolated from soil (Aga et al. 1996). 

Aga, D.S. Thurman, E.M. Formation and transport of the sulfonic acid metabolites of alachlor and metolachlor in soil. Environ. Scl Technol 2001,35,2445-2460. 

Fig. 4.4 LC-TOF MS spectra and accurate measurements for the secondary amides of alachlor (a) and acetochlor (b) sulfonic acid in a groundwater sample. The correct elemental composition for both analytes ranks at the second score position. The physico-chemical properties and the chromatographic retention times were predicted from the molecular structure (Ferrer and Thurman 2003, Fig. 4.3, with permission)...

An early investigation of alachlor metabolism by a pure culture of fungus showed significant production of 2,6-diethylaniline, which could be further metabolized (42.) More recent research, however, has shown that alachlor is dechlorinated in soil followed by conjugation with glutathione (J. Malik, Monsanto Agricultural Products Co., personal communication). The conjugates are then further metabolized to yield sulfonic and oxanilic acid derivatives of alachlor (22.), which would be very water soluble. 

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