Fabricated ultrathin magnetic nitrogen doped graphene tube as efficient and recyclable adsorbent for highly sensitive simultaneous determination of three tetracyclines residues in milk samples.

In this work, ultrathin magnetic nitrogen doped graphene tube (mNi@N-GrT) is synthetized via a template free graphitization process. The mNi@N-GrT as magnetic solid phase extraction adsorbent is used to extract three tetracyclines (TCs), showing the best extraction ability and adsorption capacity than graphene, MWCNT and magnetic MWCNT (NiFe2O4/MWCNT). The tubular structure of mNi@N-GrT can avoid the aggregation problem, provide higher active surface area and larger conjugated system. The doping of N atom will generate structural defects which will be adsorption sites for three TCs. Furthermore, the mNi@N-GrT with magnetic properties is beneficial to the recovery and recycle. The limits of detections (LODs) (S/N = 3:1) are in the range of 1.29-2.31 ng mL-1 with average recoveries from 91.6 to 109.7% in milk samples. The results demonstrate that the mNi@N-GrT is a hopeful adsorbent in the MSPE of TCs in real samples.