Laboratory experimentation is essential for our understanding of the fate and behaviour of pollutants. Many analytical techniques exist, but they all have disadvantages either in terms of sensitivity or of selectivity. The number of samples that can be analysed, the low volume of samples available during the experiment and the need to identify different degradates are all obstacles that new techniques are able to overcome. The work presented here summarizes progress in the field of metrology as concerns online solid phase extraction technology coupled with liquid chromatography followed by tandem mass spectrometry detection. Recently developed analytical techniques were validated for both 18 pesticides and their degradates and 17 pharmaceuticals and their degradates. Limits of quantification from 20 to 70 ng L(-1) for pharmaceuticals and from 15 to 25 ng L(-1) for pesticides and metabolites have been obtained, with linearity range up to 1 μg L(-1). The limits of quantification of a few nanograms per litre, the possibility of working on less than 1 mL of sample and the simultaneous quantification of the target products and their transformation products are all advantages that are demonstrated by two environmental applications. The first application concerns the evaluation of ecotoxicological effects of pesticides on aquatic organisms exposed in mesocosms. The second application aims to determine the adsorption constants of pharmaceutical molecules on soils and river sediments. For both applications, the robustness, range of linearity and limit of quantification of the developed analytical methods satisfy the requirements for laboratory experiments conducted under controlled conditions. Specific constraints generated by this type of experiment (adding CaCl2 for the adsorption study and filtration of the water coming from the mesocosms) were not found to limit the use of online SPE. These two preliminary studies show that new experimental fields are possible thanks to online solid phase extraction coupled with liquid chromatography.