Investigation on the Chemical Structure of Nonextractable Residues of the Fungicide Cyprodinil in Spring Wheat Using 13C-C1-Phenyl-Cyprodinil on 13C-Depleted Plants—An Alternative Approach to Investigate Nonextractable Residues

Abstract

¹³C-labelled cyprodinil was applied on ¹³C-depleted wheat plants with 27-fold field application rate. A control experiment applying same amounts of ¹⁴C-cyprodinil showed that main portions of the residues were detected in the cellulose (15% NER), hemicellulose (28.3% NER), and lignin fraction (23.3% NER). 16.7% were detected in water soluble polymers, 6% in both, pectin and protein fraction, and 4% in the starch containing fraction. Free cyprodinil was detectable by TLC in all fractions except lignin. A direct characterization of the residues in vivo by CP-MAS was not successful. Cell wall fractions were further analysed by liquid state NMR to determine the structure of the mobilized highly polymer/polar residues: Within lignin, where most of the residues were located at field application rate, neither intact cyprodinil nor its metabolites could not be detected. The ¹³C-label introduced was probably incorporated in the polymer as natural lignin monomers and thus are not considered as bound residues according to IUPAC definition.