Submitted to: Pittsburgh Conference
Publication Type: Abstract Only
Publication Acceptance Date: March 10, 1995
Publication Date: N/A
Technical Abstract: An HPLC method is developed for determination of imazethapyr in water. This imidazolinone herbicide, the active ingredient in Pursuit formulation, is used to control many grasses and broadleaf weeds in soybean production. Imazethapyr is extracted and concentrated from acidified water on 1000-mg cyclohexyl solid-phase cartridges. Extracted components are separated on a C18 reversed-phase column, chemically shielded to enhance separations of organic bases. Resolution is achieved through tertiary acetonitrile-water gradients at pH 7.0 and 3.0 so that imazethapyr is isolated from other co-extracted herbicide-derived chemicals. The gradient is unique in that it utilizes a dynamically changing mobile-phase acidity without the use of ionic additives such as buffers, salts, or ion-pair agents; all of which diminish column life. Under these conditions, imazethapyr elutes in 20 minutes. Photometric detection is by photodiode-array, simultaneously at 254, 220, and 199 nm with spectral bandwidths of 6, 6, and 10 nm, respectively. 2-L samples are reduced to 1-mL final volume of extract that is dissolved in initial-conditions mobile-phase. An injection volume of 250-uL furnishes a nominal detection limit of 5 ppb. Qualitative analysis is achieved through spectral comparison with a user-generated library of reference UV spectra. Quantitation is via external-standard multi-point calibration, exhibiting at least a two-order-of-magnitude linearity. Method validation is achieved through spike-recovery studies in authentic agricultural water matrices. Confirmation of analyte identity is by LC-MS through the particle-beam interface.