Methods of analysis by the U. S. Geological Survey National Water Quality Laboratory-Determination of organonitrogen herbicides in water by solid-phase extraction and capillary-column gas chromatography/mass spectrometry with selected-ion monitoring - Sandstrom, Mark; Wydoski, Duane; Schroeder, Michael; Zamboni, Jana; Foreman, William T. (Open-File Report, 1992)