ANALYSIS OF SULFONYLUREA HERBICIDES BY GAS-LIQUID-CHROMATOGRAPHY .1. FORMATION OF THERMOSTABLE DERIVATIVES OF CHLORSULFURON AND METSULFURON-METHYL

A method is described to overcome the thermal instability of sulfonylurea herbicides and thus enable their analysis by gas chromatography (GC). Methylation of chlorsulfuron by diazomethane in a variety of solvents usually yielded N-methylchlorsulfuron as the predominant product. This derivative was not stable to GC conditions, forming the N-methylsulfonamide. With diazomethane in either acetone or ethyl acetate and with longer reaction times substantial quantities of the N,N'-dimethyl derivatives of chlorsulfuron and metsulfuron-methyl were formed, which were characterized by GC-MS (EI and CI). These derivatives were thermostable and gave symmetrical GC peaks with good responses to both electron capture and nitrogen-phosphorus detectors. Reaction conditions were optimized in ethyl acetate to maximize yields of the N,N'-dimethyl derivatives. Formation of the derivatives was shown to be linear over the range 0.1-10 mug, and they were suitable for determination at residue levels.