Introduction Sulfonylureas are an important group of systemic herbicides mainly used for the control of annual and perennial weeds in cereals or root crops in early growth stages of the cultivations. They are characterised by their broad spectrum weed control at low application rates, good crop selectivity and low acute and chronic animal toxicity. They are widely applied as selective pre and post- emergence herbicides and therefore, high is the possibility their residues to contaminate water, soil and air and also be accumulated in grains. Comparison of the determination of sulfonylurea herbicides residues with two analytical techniques by LC/MS/MS Kappatos Petros 1, Bempelou Eleftheria 2, Vontas John 1, Liapis Konstantinos 2 1 Pesticide Science Laboratory, Agricultural University of Athens, 75, Iera Odos str., GR , Athens, Greece, 2 Laboratory of Pesticide Residues, Benaki Phytopathological Institute, 8 St. Delta str., GR Kifissia, Greece In the present study, the determination of nicosulfuron, thifensulfuron-methyl, tribenuron-methyl, triasulfuron, azimsulfuron, metsulfuron-methyl and rimsulfuron has been achieved in wheat flour with the use of two different sample preparations. The first was based on Quechers method and the second one on a multiresidue method based on extraction with ethyl acetate. Chromatographic separation and determination was common for both techniques and was achieved by LC/MS/MS. Both methods were validated in three fortification levels, 0.01mg/kg, 0.05mg/kg and 0.1mg/kg in accordance with the requirements of SANTE/11945/2015. The Maximum Residue Level for all the sulfonylureas tested in wheat is 0.01mg/kg (EU Reg 617/2014). The assumption of a conversion factor equal to 1 was adopted. Linearity was examined with the analysis of matrix-matched standards of mg/kg (5 levels) for both methods. MS detector gave linear response over the studied range of concentrations and the least–squares linear regression analysis of the data provided excellent correlation for all compounds tested (r>0.99). All the calculated RSD values were ≤ 20%. The comparison of the obtained results was in favor of the modified method of the multiresidue method based on extraction with ethyl acetate for the determination of sulfonylureas in cereals. Therefore, this method is considered to be accurate, precise, and sensitive for quantitative and qualitative analysis of sulfonylurea herbicides in cereals at low levels required by legislation. Both the tested analytical techniques were successfully applied to different domestic and imported samples of cereals and no residues were determined. Results REFERENCES 1. European Union Reference Laboratory for Pesticide Residues in Fruits & Vegetables. Analysis of pesticide residues in fruit and vegetables with ethyl acetate extraction using gas and liquid chromatography with tandem mass spectrometric detection. Almeria, Spain. 2. Anastassiades M., Lehotay S.L., Stajnbaher D., Schenck F.J. (2003). Fast and easy multiresidue method employing acetonitrile extraction/ partitioning and “Dispersive Solid Phase extraction” for the determination of pesticide residues in produce. J. AOAC Int., 86 (2003) 3.Commission of the European Union, Doc No SANTE/11945/2015. Guidance document on analytical quality control and method validation procedures for pesticides residues analysis in food and feed. Chromatographic analysis and validation of analytical methods A Varian [2x prostar 210 (LC) and 1200 L (quadrupole MS/MS)] LC- MS/MS was used for the determination sulfonylureas. Column: Varian Polaris C18-A column, (5 cm length, 2 mm internal dimension and 5 μm particle size) at ambient temperature (25 ± 4 o C). Elution solvents: water supplemented with HCOOH (A) and acetonitrile supplemented HCOOH (B). Flow: 0.25 mL/min Elution program: gradient, starting with 80% of solvent A and 20% of solvent B, reaching the 100% of solvent B at 9 min, remaining there for 6 min and returning to its first constitution at min and remaining until min. The electrospray ionization mode was either in positive or in negative mode, using nitrogen as nebulizer gas at 50 psi. The compounds were grouped according to their optimum determination in each ionization mode. Figure 1. Determination of sulfonylureas residues in wheat flour in three fortification levels (0.01, 0.05 and 0.1mg/kg) based on extraction with ethyl acetate, in either positive or negative ionization mode. Figure 2. Determination of sulfonylureas residues in wheat flour in three fortification levels (0.01, 0.05 and 0.1mg/kg) based on Quechers, in either positive or negative ionization mode. As proved, Quechers did not provide acceptable results at the lowest fortification level, which is equal to the MRL set by the EU, in neither ionization mode. Negative mode Positive mode Analyte Product Ion (m/z) Parent Ion (m/z) Collision energy (eV) Capillary (V) Positive ionization Nicosulfuron411182, 213, Thifensulfuron- methyl , 205, 141 Tribenuron-methyl396155, 181, 199 Triasulfuron402167, 141, 167 Negative ionization Azimsulfuron423214, 135, Metsulfuron-methyl380182, 139, 107 Rimsulfuron430186, 179, 275 Table 1. Parent and product ions for the determination of sulfonylureas herbicides in wheat flour using LC/MS/MS.