High performance liquid chromatography-tandem mass spectrometry for the analysis of 10 pesticides in water: a comparison between membrane-assisted solvent extraction and solid phase extraction.

This work describes the application of two sample preparation methods: membrane-assisted solvent extraction (MASE) and solid phase extraction (SPE) in combination with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) for the determination of 10 pesticides in surface and ground water. Optimal extraction conditions for MASE were 60 min extraction time at 30 degrees C with a solvent volume of 100 microL toluene. 5 microL of the toluene extract were directly injected in the HPLC-MS-MS system. Concerning SPE, two materials were tested and C18 was superior to Oasis HLB. Complete desorption was ensured by desorbing the SPE (C18) cartridge with 3 mL of an acetonitrile/methanol mixture (1:1). After evaporation, the extract was injected in the analytical system. Analyte breakthrough was not found for the investigated compounds. For both methods, high extraction yields were achieved, in detail 71% (metalaxyl) till 105% (linuron) for MASE and 52% (ethiofencarb) till 77% (prometryne) for SPE (C18). Detection limits were in the low ng/L range for both methods and precision, expressed as the relative standard deviation (RSD) of the peak areas was below 13%. Five real water samples were analyzed applying both extraction methods. The results were in good agreement and standard addition proved that no matrix effects (such as ion suppression) occurred. In this comparison SPE has the potential of larger sensitivity whereas faster analysis and slightly better recoveries were achieved with MASE. MASE shows potential to be a promising alternative to the conventional off-line SPE concerning low to medium polar compounds.