Graphene particles supported on silica as sorbent for residue analysis of tetracyclines in milk employing microextraction by packed sorbent

This paper describes the use of graphene-based sorbents for determination of four tetracyclines in milk. The synthesized materials were combined with microextraction by packed sorbent (MEPS) to act as the sample preparation step. The extraction performance of these sorbents was compared to commercial phases, and graphene supported on silica provided the best results. The analytical method optimization was carried out by employing experimental design. Firstly, an evaluation of the experimental variables (elution solvent, use of EDTA, ionic force, and pH of the washing solution) was made by a 2(4-1) factorial experimental design. The variables sampling, washing and elution cycles of MEPS were further optimized under a full 2(3) experimental design. The validation parameters were determined under optimized conditions resulting in a linearity ranging from 15 to 110g/L with R-2 values above 0.98, and LOQs ranging from 0.05 to 0.9g/L. The accuracy ranged from 87.9 to 118.4% and intra/inter-day precision reported by the RSDs were lower than 19%. The proposed and validated method was successfully applied to the analysis of 11 milk samples from different animals, revealing traces of tetracyclines in only two of them. This study focused on the evaluation of graphene-based sorbents combined with MEPS for tetracycline analysis provided equivalent or even better results than other proposed methods, suggesting being a sensitive, fast and reliable alternative method for the determination of tetracyclines in milk samples.