A method for the simultaneous determination of selected maize and grain herbicides (amidosulfuron, N-([{[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl}amino)sulfonyl]-N-methylmethanesulfonamide; bentazone, 3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-one2,2-dioxide; 2,4-D, (2,4-dichlorophenoxy)acetic acid; MCPA, (4-chloro-2-methylphenoxy)acetic acid; metosulam, N-(2,6'-dichloro-3-methylphenyl)-5,7-dimethoxy[1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonamide) and their transformation products (TPs) (8-hydroxybentazone, 1H-2,1,3-benzothiadiazin-4(3H)-one,8-hydroxy-3-(1-methylethyl)-2, 2-dioxide; bifenox acid, 5-(2,4-dichlorophenoxy)-2-nitrobenzoic acid; clodinafop acid; 2,4-dichlorophenol; 4-chloro-2-methylphenol) in environmental waters was developed. The procedure combines a solid-phase extraction (SPE) with column liquid chromatography-tandem mass spectrometry detection utilizing a pneumatically assisted and heat-assisted electrospray interface in negative mode. The extraction of analytes from filtered drainage or river water samples was performed using as sorbent a graphitized carbon. The recovery, for drinking water, ranged from 91 to 98%, and from 84 to 95% for river water. Excellent method precision was demonstrated with percent relative standard deviation of less than 10% for all analytes at fortification level. Detection limits were at level of few nanograms per liter, except for 2,4-dichlorophenol and 4-chloro-2-methylphenol, that was in the range of tens of nanogram per liter. The present methodology was used for searching in river and drainage waters of maize-grain fields of the Tiber valley, during a typical period of herbicides application from April to July 2001. The levels detected of four compounds were in the range of: non-detectable (ND)-6.1, ND-27, ND-1.9 and ND-0.5 mug l(-1), for MCPA, bentazone, 8-hydroxybentazone and 2,4-D, respectively. Detectable amounts of bentazone-8-hydroxy at level of 0,3 mug l(-1) was found to be transported into river. The highly satisfactory results for all target analytes demonstrate the potential of liquid chromatography-tandem mass spectrometry for the identification and the quantification of the polar and acidic herbicides at below 100 ng l(-1) levels. (C) 2002 Elsevier Science B.V. All rights reserved.