Stir bar sorptive extraction coupled to liquid chromatography-tandem mass spectrometry for the 2 determination of pesticides in water samples: method validation and measurement uncertainty

Authors 4 Christelle Margoum, Céline Guillemain, Xi Yang, Marina Coquery 5 a Irstea, UR MALY, 5 rue de la Doua, CS 70077, F-69626 Villeurbanne Cedex, France 6 b State Key Laboratory of Pollution Control and Resource Reuse, Nanjing University, 210093 Nanjing, China 7 *corresponding author Tel. +33472208711; fax: +33478477875; E-mail address: [email protected] 8 9 10 Abstract 11 Stir bar sorptive extraction followed by liquid desorption and high performance liquid 12 chromatography with tandem mass spectrometry (SBSE-LD-LC-MSMS) has been developed for the 13 determination of 15 pesticides or selected metabolites from different families (herbicides, insecticides, 14 fungicides) in surface water samples. The optimization of parameters that could influence SBSE-LD 15 efficiency was carried out by means of experimental design. Optimized conditions were established as 16 follows concerning extraction time, stirring speed, aqueous medium characteristics (ionic strength and 17 polarity) and back desorption solvent and time, respectively: 3 h (800 rpm), addition of 10% of sodium 18 chloride, no addition of methanol as organic modifier, and 15 min ultrasonic desorption in equivolume 19 mixtures of acetonitrile-methanol. A specific and thorough cleanup procedure was developed and 20 applied to each stir bar to avoid possible carry-over between consecutive extractions with the same stir 21 bar. Pesticide quantification in water was achieved thanks to matrix matched calibration. Mean 22 recoveries ranged from 93 to 101% (RSD < 17%, n=30). Validated limits of quantification in matrix 23 were between 0.02 and 1 μg L, depending on the compound. A specific experimental design was 24 conducted to evaluate the measurement uncertainty, which was comprised between 13 and 51%, 25 whatever the pesticide and the concentration level. The applicability of the SBSE-LD-LCMSMS 26 method was evaluated by analyzing surface water samples and by comparing with conventional solid 27 phase extraction-LC-MSMS procedure. 28 29