Determination of herbicides by solid phase extraction gas chromatography-mass spectrometry in drinking waters

Asolid phase extraction (SPE) method has been optimized for the gas chromatography–mass spectrometry (GC–MS) simultaneous determination of herbicides belonging to the following different families: carbamate (molinate), atrazines (atrazine, propazine, simazine, ametryne, cyanazine, terbutylazine, deethylterbutylazine, deethylatrazine), dinitroaniline (trifluralin, pendimethalin), chloroacetamide (alachlor, metolachlor). Different solid substrates have been compared (C18, cyano, styrene–divinylbenzene, phenyl, graphitic carbon). The type of conditioning and elution solvent, its volume, and the sample flow rate have been considered as variables affecting the recovery yields of the herbicides. The optimized experimental conditions are C18 phase conditioned with 3mL acetone, loaded with 1 L water sample at 5mL min−1, and eluted with 3mL acetone. Good recoveries (included between 79% and 99%) and R.S.D. (included between 2% and 12%) have been obtained for all analytes, except for deethylatrazine whose recovery was 46±7%. The recovery of deethylatrazine increases up to 94±17% if a non-porous graphitic carbon is coupled to the C18 phase, keeping the other parameters constant as optimized. The optimized method has been successfully checked for the identification and quantitation of the selected herbicides in raw and drinking water samples, with quantitation limits as low as 0.01gL−1, fully in agreement with the current legislation. The method is easily routinable. After development, the method is currently routinely applied for the analysis of herbicides in waters and, up today, more than one thousand samples have been analysed at the “Laboratorio della Societ`a Metropolitana Acque di Torino” (Laboratory of the Municipal Waterworks of Turin) in charge of the control of drinking water quality in Torino.