Restricted access materials for sample clean-up in the analysis of trace levels of tetracyclines by liquid chromatography: Application to food and environmental analysis

Restricted access materials (RAM) based on alkyl diol silica (ADS) porous particles were evaluated for the sample clean-up in tetracyclines analysis in milk and water samples by liquid chromatography. RAM with C4, C8 and C18 bonded to the inner pore surfaces were tested, with C8 providing the best performance. A switching column LC system which combines an ADS C8 RAM column and an analytical C18 column connected to a fluorimetric detector was used for tetracyclines analysis. The RAM clean-up removed large peaks that otherwise appeared in the initial time window of the chromatograms, attributed to proteins in milk samples and humic substances in water samples. Thus, quantification of analytes in real samples, especially of the most polar compounds such as oxytetracycline and tetracycline, was clearly improved.