POLAROGRAPHIC-DETERMINATION OF SOME PESTICIDES CONTAINING NITRO-GROUP - APPLICATION TO A STUDY OF ADSORPTION ON LIGNIN

The polarographic method proved suitable for investigation of adsorption of acifluorfen (I) (5-[2-chloro-4-(trifluoromethyl)phenoxy]-2'-nitrobenzoic acid) on lignin. Polarographic reduction of acifluorfen in aqueous buffers (pH < 7) is complicated by adsorption of the reduction product. In acidic media the reduction of the protonated hydroxylamino group occurs at such positive potentials that only a single six-electron wave is observed. In buffers containing 33% (w/w) ethanol the effects of the adsorption are eliminated and the reduction of the hydroxylamino group occurs at more negative potentials, so that one four-electron and one two-electron wave are observed. Splitting of the four-electron wave at pH > 7 is attributed to a decrease in protonation rate of the reduction intermediate. Unsubstituted p-nitrophenyl phenyl ether (II) shows an analogous behavior. Reduction wave of the nitro group can be used for determination of aciflurofen (I), fluorodifen (III), oxyfluorfen (IV), and bifenox (V) in the 1 x 10(-5) to 5 x 10(-4) M range. Adsorption of acifluorfen depends on the nature of the lignin and pH.