Preconcentration of morphine and codeine using a magnetite/reduced graphene oxide/silver nano-composite and their determination by high-performance liquid chromatography.

•A Fe3O4/rGO/Ag nanocomposite (NC) was synthesized and characterized.•The synthesized NC was used as a magnetic solid phase extraction (MSPE) sorbent.•Fe3O4/rGO/Ag NC can be quickly isolated from the sample solution by a magnet.•The MSPE‒HPLC method is accurate and sensitive to detect morphine and codeine.•Various blood and urine samples were analyzed by the presented method.