Magnetic solid phase extraction based on graphene oxide/nanoscale zero-valent iron for the determination of tetracyclines in water and milk by using HPLC-MS/MS

A magnetic solid-phase extraction (MSPE) based on graphene oxide/nanoscale zero-valent iron (GO/nZVI) coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was proposed for the determination of trace tetracycline antibiotics (TCs) in water and milk. GO covered nZVI was self-assembled by electrostatic forces by varying the pH. Several important parameters affecting the MSPE procedure have been investigated. The pH value is a key factor in the whole MSPE process. An appropriate pH can not only improve adsorption and desorption efficiency, but also enable the extraction of TCs from GO/nZVI by using deionized water. Optimal conditions were then used for the extraction of TCs from real samples, prior to HPLC-MS/MS determination in the positive ESI mode of multiple reaction monitoring (MRM) using a ZORBAX Eclipse Plus C-18 column. The proposed method achieved low limits of quantitation in the range of 8.05-83.19 ng L-1 and 17.42-182.75 ng L-1 for water and milk samples, respectively, and satisfactory recoveries in the range of 84.2-105.5% with intra-day RSD in the range of 0.6-2.5% and inter-day RSD in the range of 1.2-9.2% for the spiked water sample and from 87.0% to 101.8% with intra-day RSD in the range of 1.1-5.4% and inter-day RSD in the range of 2.0-9.7% for the spiked milk sample.