Gas Chromatographic Determination of Ametryn and Its Metabolites in Tropical Root Crops

Residue analysis of the herbicide ametryn (2-methyIthio-4-ethylamino-s-isopropylamino-s-triazine) is widely known but an analytical method for determining its metabolites has not yet been reported in the literature. A method has been developed for the extraction and determination of ametryn and 3 metabolites, 2-methylthio-4-amino-6-isopropylammo- s-triazine (GS-11354), 2-methylthio-4,6-diamino-.s-triazine(GS- 26831), and 2-methylthio-4-amino-6-ethylamino-s-triazine (GS-11355) in taniers, yams, cassava. Residues were extracted from crops with ethyl acetate-toluene (3 + 1 v/v), using a Polytron homogenizer and anhydrous sodium sulfate added for drying. The extracts were cleaned up by automated gel permeation chromatography on Bio-Beads SX-3 gel in the same solvent system. Quantitative determination was performed by gas chromatographic (GC) analysis on a column packed with 5% DEGS-PS on 100-120 mesh Supelcoport using either an N-P detector or a flame photometric detector (FPD) in the sulfur mode. Minimum detection by the flame photometric detector is 10 ng each for ametryn, GS-11354, and GS-11355 and 21 ng for GS-26831; by the N-P detector, 0.3 ng of each component gives easily quantitatable peaks. On a parts per million basis, starting with 25 g sample, the FPD detected a minimum level of 0.04 p.g/g each for ametryn, GS-11354, and GS-11355, and 0.08 p.g/g for GS-26831. The N-P detector could detect 0.0024 p.g/g for all 4 compounds. In addition to superior sensitivity, instrumental conditions allowed the complete separation of components in 10 min, for the N-P detector; more than 30 min was required for the FPD. Recoveries from fortified crops ranged from 67 to 111% at levels of 0.1-1.0 μg/g.