Determination of carbamate residues in high-fat cheeses by ultra-high performance liquid chromatography–tandem mass spectrometry using zirconia-based QuEChERS A.M. Hamed, D. Moreno-González, L. Gámiz-Gracia, A.M. García-Campaña Department of Analytical Chemistry, Faculty of Sciences, University of Granada, Campus Fuentenueva s/n, 18071 Granada, Spain amgarcia@ugr.es FQM 302: Quality in food, environmental and clinical analytical chemistry Introduction Carbamate (CRB) are widely used pesticides in agricultural activities, that can enter into the food chain from raw to processed foods, having adverse health effects. Due to their high lipid content, cheese may be considered a good indicator of indirect contamination of foodstuffs by CRB residues. The main components of cheese are fat, proteins, salt and carbohydrates. Due to the complexity of these matrices, the determination of CRB residues in cheese is still a challenge, requiring sample treatments with exhaustive clean-up. In this work, a new method for the determination of 28 CRBs in high-fat cheeses using ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) combined with QuEChERS is proposed as a good alternative. Moreover, a new sorbent (SupelTM QuE Z-Sep+) has been tested for dispersive solid phase extraction (dSPE). CHROMATOGRAPHIC SETTINGS Sample treatment Variable Optimum value Column C18 column (Zorbax Eclipse plus RRHD 50 mm x 2.1 mm, 1.8 mm) Mobile phase composition solvent A: Water (0.01% formic acid) solvent B: MeOH (0.01% formic acid) Gradient program (A:B) 0:0.7 min (95:5) 0.7:1.2 min (80:20) 2.5:3 min (50:50) 6.5:8.5 min (0:100) 8.5:9 min (95:5) 9:10.5 min (95:5) Mobile phase flow rate 500 µl min-1 Sample solvent H2O: MeOH (70:30 v/v) Injection volume 10.0 µl Column temperature 25°C Supel™ QuE Z-Sep+ consists of both C18 and zirconia bound to the same silica particles. The C18 phase binds fats through hydrophobic interaction, while the zirconia acts as a Lewis acid, attracting compounds with electron donating groups. Retention mechanism for fats on Z-Sep+ Z-Sep+ was compared with other sorbents previously reported for dSPE of fatty matrices (i.e. mixture of C18 and PSA), resulting in reduced matrix effects (ME) without any significant decrease of analyte recoveries. Results Extracted ion chromatogram of a spiked Gorgonzola cheese sample applying the proposed method (10 µg kg-1 of each CRB). Diagram of the proposed QuEChERS procedure ANALYTICAL PERFORMANCE CHARACTERISTICS Range of values of studied parameters for 28 CRBs LOQs lower than the default maximum residue limit in the case of milk were obtained for all the CRBs . LODs (µg kg-1): 0.1 -1.6 LOQs (µg kg-1): 0.5 -5.4 Intraday precision (RSD %): 4- 13% (n=9) Interday precision (RSD %): 3 - 13% (n=9) Satisfactory recoveries were obtained for Gorgonzola, Roquefort and Camembert cheeses, with satisfactory RSD, fulfilling current legislation Precision satisfies the requirements established in current legislation Conclusions Recovery: 70 –115 % (RSD: <13%, n=9) UHPLC–MS/MS combined with a QuEChERS based on the use of Z-Sep+ for dSPE is a rapid, convenient and high throughput method for clean-up and determination of CRB residues in high-fat cheese samples at trace concentrations. The results in terms of sensitivity, selectivity, accuracy, cleanliness of extracts and ME indicated that this new sorbent is an interesting alternative for dSPE of matrices with a high fat content. Matrix effect evaluation: ME (%): 2 -31.3% ME were moderate for all CRBs AMH thanks the “Erasmus Mundus - Al Idrisi II program” for a doctoral grant. The authors gratefully acknowledge the financial support of the Junta de Andalucía “Excellence Project Ref: P12-AGR-1647”. Acknowledgment