Direct extraction of tetracyclines from bovine milk using restricted access carbon nanotubes in a column switching liquid chromatography system

•The RACNTs were unprecedentedly used to analyze tetracyclines in bovine milk.•The RACNTs promoted the exclusion of proteins and other interferents from milk.•The developed method exhibited suitable validation parameters.•The method is simple, reproducible, quick and cheap.

This paper describes, for the first time, the use of restricted access carbon nanotubes (RACNTs) in the analysis of tetracyclines from milk samples, in a multidimensional liquid chromatographic system. Milk samples were initially acidified and centrifuged, and then the supernatant was directly analyzed in a column switching system in backflush configuration employing an extraction column of RACNTs. The sorbent was able to exclude all the remained proteins in less than 2.0 min. The method was linear from 50 to 200 μg L−1 and the coefficients of determination (r2) were 0.997, 0.992, 0.994 and 0.998 for oxytetracycline (OXI), tetracycline (TC), chlortetracycline (CTC) and doxycycline (DOX), respectively. The analytical range included the maximum residue limits established by the regulatory agency.