A simple pH-responsive magnetic solid phase extraction method was developed using graphene oxide-coated nanoscale zerovalent iron nanoparticles as an efficient adsorbent prior to HPLC-MS/MS for determination of ultra-trace quinolones in milk samples. Various parameters affecting maghemite synthesis and separation such as pH of sample solution, amount of magnetic adsorbent, eluent type and volume were optimized. The limits of detection are from 3.1 ng L to 13.3 ng L . The intra- and inter-precision values are in the range of 2.9-6.9% and 7.6-15.1%, respectively. Recoveries are from 82.4% to 103.9%. Therefore, this simple and sensitive method is suitable for detecting ultra-trace quinolone residues in milk. This article is protected by copyright. All rights reserved.