Optimization and validation of UHPLC tandem mass spectrometry method for determination of multi-class pesticide residues in bovine liver applying QuEChERS sample preparation - Elizabeta Dimitrieska-Stojkovikj; Alekandra Angjeleska; Hajrulai Musliu, Zehra; Uzunov, Risto; Biljana Stojanovska-Dimzoska; Gordana Ilievska; Goran Stojkovikj (Faculty of Veterinary Medicine-Skopje, Ss. Cyril and Methodius University in Skopje, North Macedonia, 2015)