Multiresidue determination of pesticides in drinking and related waters bygas chromatography/mass spectrometry after solid-phase extraction: Interlaboratory study

As part of a project funded by the European Commission (EC) for the develop ment and evaluation of multiresidue methods for analysis of drinking and re lated waters, 15 European laboratories evaluated a method using styrene-div inylbenzene copolymer solid-phase extraction followed by gas chromatography /mass spectrometry. The main aim of the study was to evaluate whether the m ethod meets the requirements of EC Directive 98/83 in terms of accuracy, pr ecision, and detection limit for 22 pesticides according to the following r equirements: limit of detection, less than or equal to0.025 mug/L; accuracy , expressed as recovery between 75 and 125%; and precision, expressed as re peatability relative standard deviation of the method of < 12.5% and as rep roducibility relative standard deviation of the method of < 25%. Analyses f or unknown concentrations were performed with fortified commercial bottled and tap waters. All laboratories were able to achieve detection limits of 0 .01 mug/L for all pesticides except dimethoate and desisopropylatrazine (0. 02 mug/L). The criteria for repeatability were met for all compounds except trifluralin, dimethoate, and lindane in bottled water and chlorpyrifos, di methoate, and lindane in tap water. The criteria for reproducibility were m et for all compounds except trifluralin, dimethoate, and lindane in bottled water and pendimethalin, chlorpyrifos, dimethoate, terbutryn, and lindane in tap water. In terms of accuracy, the method meets the requirements for a ll pesticides in both matrixes, except for lindane in bottled water and lin dane and chlorpyrifos in tap water.