Microwave-Assisted Extraction Coupled with Gas Chromatography/Electron Capture Negative Chemical Ionization Mass Spectrometry for the Simplified Determination of Imidazolinone Herbicides in Soil at the ppb Level

The imidazolinones are a significant new class of low-use-rate, reduced-environmental-risk herbicides for protection of a wide variety of agricultural commodities. Because of their low rates of application, residues of the imidazolinones in soil need to be monitored at the low ppb level. Current methodology for this purpose involves an exhaustive base extraction followed by a laborious, time-consuming cleanup procedure to permit analysis at the 5 ppb level. Using imazethapyr, the most widely utilized member of the class, as a representative, we have achieved not only a limit of quantitation of 1 ppb but also a greatly simplified cleanup procedure by combining microwave-assisted extraction technology with gas chromatography/electron capture negative chemical ionization mass spectrometry. On a variety of soil types covering a fortification range of 1−50 ppb, an average recovery of 92% with a standard deviation of 13% was achieved. Control soil extracts gave apparent residues of