Simplified Determination of Imidazolinone Herbicides in Soil at Parts-per-Billion Level by Liquid Chromatography/ Electrospray Ionization Tandem Mass Spectrometry

Abstract

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 imidazolinones in soil need to be monitored at low parts-per-billion (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/ECNCI) and for determining imidazolinones in water by using liquid chromatography/electrospray ionization mass spectrometry (LC/ESMS) and liquid chromatography/electrospray ionization tandem MS (LC/ESMS/MS). By merging the extraction and cleanup procedures for determining imidazolinones 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 soil 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. These results were almost identical to those previously reported for GC/ECNCI.