Determination of Tetracycline Residues by Liquid Chromatography Coupled with Electrochemical Detection and Solid Phase Extraction

A liquid chromatography based on the reverse phase separation and a solid phase extraction (SPE) procedure using a phenyl-silica sorbent for the simultaneous separation and extraction/preconcentration of six tetracyclines was studied and optimized. An amperometric detector using a polycrystalline gold electrode operating under both DC and IPAD conditions was tested for the determination of the selected tetracyclines. Under optimal SPE and chromatographic conditions, the limit of detection of the investigated tetracyclines comprised between 50 nM (25 mu g L-1) and 75 nM (37 mu L-1), and the dynamic linear range spanned generally over 3 orders of magnitude, when the electrochemical detector was used under DC conditions at a constant applied potential of 1.6 V vs Ag/AgCl. The analytical method was successfully tested for the determination of tetracyclines in milk samples ((UHT low-fat, fresh pasteurized, and powdered milk) with reproducibility and recovery levels ranged between 3.1%-5.6% and 70%-118%, respectively.