Alachlor oxanilic 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%. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

Figure 7 Formation of ethanesulfonic acid and oxanilic acid metabolites from the reaction of a chloroacetanilide herbicide (alachlor) with glutathione and other enzymes (Field and Thurman (1996) reproduced hy permission of American Chemical Society from Environ. Sci. Technol, 1996, 30, 1413-1417).

A variety of neutral degradation products of the chloracetanilide herbicide alachlor was identified [63, 115]. However, the ionic metabohtes such as the oxoethanesulfonic acid derivative appear to be of more significance, as they are readily leached to groundwater. WMe alachlor itself is amenable to GC-MS, its ionic metabolites are not. Initially, GC-MS, LC-UV-DAD, and fast-atom bombardment MS-MS were applied in the analysis and identification of such metabolites [119]. Subsequently, the potential of LC-ESI-MS in this area was recognized [120]. Both oxanilic acid and oxoethanesulfonic acid metabohtes of alachlor, acetochlor and metolachlor were identified in snrface water and gronnd water, and subsequently determined with detection limits at the 0.01-pg/l level using off-hne SPE in combination with LC-MS [120]. 

R.A. Yokley, L.C. Mayer, S.-B. Huang, J.D. Vargo, Analytical method for the determination of metolachlor, acetochlor, alachlor, dimethenamid, and their corresponding ethanesulfonic and oxanillic acid degradates in water using SPE and LC-ESI-MS-MS, Anal. Chem., 74 (2002) 3754. 

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. 

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). 

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