SIMPLIFIED DETERMINATION OF IMIDAZOLINONE HERBICIDES IN SOIL AT PARTS-PER-BILLION LEVEL BY LIQUID-CHROMATOGRAPHY ELECTROSPRAY-IONIZATION TANDEM MASS-SPECTROMETRY

Imidazolinones are a significant new class of low-use-rate, reduced-en vironmental-risk herbicides for protection of a wide variety of agricu ltural commodities, Because of their low rates of application, residue s of imidazolinones in soil need to be monitored at low parts-per-bill ion (ppb) levels, Greatly simplified cleanup procedures were reported recently for determining imidazolinones in soil at the 1 ppb level by combining microwave-assisted extraction (MAE) with gas chromatography/ electron capture negative chemical ionization mass spectrometry (GC/EC NCI) and for determining imidazolinones in water by using liquid chrom atography/electrospray ionization mass spectrometry (LC/ESMS) and liqu id chromatography/electrospray ionization tandem MS (LC/ESMS/MS). By m erging the extraction and cleanup procedures for determining imidazoli nones in soil with LC/ESMS/MS, instrumental analysis time was reduced to that approximating sample preparation time, and the drawbacks of in situ methylation required for GC/ECNCI were eliminated, Recoveries of imazethapyr, the most widely used imidazolinone, from a variety of so il types fortified at 1-50 ppb averaged 92% with a standard deviation of 9.7%. Control soil extracts gave apparent residues of < 0.2 ppb. Th ese results were almost identical to those previously reported for GC/ ECNCI.