U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

Routine Determination of Sulfonylurea, Imidazolinone, and Sulfonamide Herbicides at Nanogram-Per-Liter Concentrations by Solid-Phase Extraction and Liquid Chromatography/Mass Spectrometry

By Edward T. Furlong, Mark R. Burkhardt, Paul M. Gates, Stephen L.Werner, and William A. Battaglin

This report is available in pdf format: Furlong.pdf

ABSTRACT

Sulfonylurea (SU), imidazolinone (IMI), and sulfonamide (SA) herbicides are new classes of low-application-rate herbicides increasingly used by farmers. Some of these herbicides affect both weed and crop species at low dosages and must be carefully used. Less is known about the effect of these compounds on noncrop plant species, but a concentration of 100 ng/L (nanograms per liter) in water has been proposed as the threshold for possible plant toxicity for most of these herbicides. Hence, analytical methods must be capable of detecting SUs, IMSs, and SAs at concentrations less than 100 ng/L in ambient water samples. The authors developed a two-cartridge, solid-phase extraction method for isolating 12 SU, 3 IMI, and 1 SA herbicides by using high-performance liquid chromatography/ electrospray ionization-mass spectrometry (HPLC/ESI-MS) to identify and quantify these herbicides to 10 ng/L. This method was used to analyze 196 surface- and ground-water samples collected from May to August 1998 throughout the Midwestern United States, and more than 100 quality-assurance and quality-control samples.

During the 16 weeks of the study, the HPLC/ESI-MS maintained excellent calibration linearity across the calibration range of 5 to 500 ng/L, with correlation coefficients of 0.9975 or greater. Continuing calibration verification standards at 100-ng/L concentration were analyzed throughout the study, and the mean measured concentrations for individual herbicides ranged from 93 to 101 ng/L. Mean recovery of herbicides from 27 reagent water samples spiked at 50 and 100 ng/L ranged from 39 to 92 percent and averaged 73 percent. The standard deviation of recoveries ranged from 14 to 26 percent and averaged 20 percent. This variability reflects multiple instruments, operators, and the use of automated and manual sample preparation. Spiked environmental water samples had similar recoveries, although for some herbicides, the sample matrix enhanced recoveries by as much as 200 percent above the spiked concentration. This matrix enhancement was sample and compound dependent. Concentrations of herbicides in unspiked duplicate environmental samples were typically within 25 percent of each other. The results demonstrate the usefulness of HPLC/ESI-MS for determining low-application-rate herbicides at ambient concentrations.