USE OF A SILYLATION PROCEDURE AND C-13-NMR SPECTROSCOPY TO CHARACTERIZE BOUND AND SEQUESTERED RESIDUES OF CYPRODINIL IN SOIL

Soil-bound residues of the fungicide cyprodinil (4-cyclopropyl-6-methy l-2-phenylaminopyrimidine), which was labeled with C-13 and C-14 eithe r in the phenyl ring or the pyrimidyl ring, were analyzed by a silylat ion procedure and C-13-NMR spectroscopy. After a 6-month incubation of soil with 3 or 500 ppm cyprodinil, bound residues amounted to about 5 0% and 18% of the initial radioactivity, respectively. The isolated hu mic acid fraction and the NaOH-extracted soil (the humin fraction) wer e suspended in chloroform and silylated by overnight shaking with trim ethylchlorosilane. Analysis of the silylated extracts by C-13-NMR reve aled that the formation of soil-bound residues in the 500 ppm samples involved: (1) sequestration of the unaltered or slightly altered fungi cide in the humin fraction and (2) cleavage of the cyprodinil molecule between the aromatic rings followed by covalent binding of the separa ted moieties to humic acid. The sequestered fungicide (phenyl label) g enerated triplet NMR signals at 121.0, 125.0, 128.7, and 135.8 ppm, wh ich closely coincided with the resonances shown by the silylated stand ard of cyprodinil. TLC analysis indicated that, in the 3-ppm samples, cleavage products were also subject to sequestration in humin. As dete rmined by size-exclusion chromatography, the molecular size of the hum ic acid fraction with the incorporated cleavage products was in the ra nge of 2 x 10(3) Da.