Validation of a new method based on salting-out assisted liquid-liquid extraction and UHPLC-MS/MS for the determination of betalactam antibiotics in infant dairy products.

In this work a new multiresidue method has been developed for the determination of 15 betalactam antibiotics in infant milk and yogurt based on follow-on milk by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The separation was achieved in 6min, using a Kinetex Biphenyl Core-Shell column (50mmx2.1mm, 1.7µm), with a mobile phase of water with 0.05% acetic acid and methanol. The analytes were detected in ESI+ with multiple reaction monitoring mode and fragmentation conditions were optimized to obtain the highest sensitivity. The use of a biphenyl bonded column allowed to obtain a satisfactory selectivity for all the studied analytes. Moreover, ion-pair salting-out assisted liquid-liquid extraction (IP-SALLE) has been proposed as sample treatment and optimized by means of experimental design. Under optimum conditions, the recoveries for fortified samples ranged from 79% to 93%, (RSD <7.5%). The limits of quantification were lower than 9.0µgkg-1, showing the high sensitivity and applicability of this fast and simple method. The results in terms of analysis time, sensitivity and accuracy showed the suitability of this procedure for the monitoring of betalactam residues in different infant foods.