Development of a High Pressure Liquid Chromatography with Diode Array Detection Method for the Determination of Four Tetracycline Residues in Milk by Using QuEChERS Dispersive Extraction

QuEChERS (quick, easy, cheap, effective, rugged and safe) dispersive extraction was applied for the extraction of tetracyclines (oxytetracycline, tetracycline, chlorotetracycline and doxycycline) from milk. Target analytes were determined by an accurate and sensitive chromatographic analytical method, which was validated in terms of 2002/6572/EC decision. The analytes were separated on an Orbit 100C4 (5 &mu
m, 250 &times
4.0 mm) analytical column under a gradient mobile phase composed of a mixture of 0.01 M oxalic acid, 10&minus
4 M Na2EDTA and acetonitrile. For the extraction of isolated compounds from sorbent, a methanol and 0.01 M oxalic acid mixture (1:1 v/v) was used, leading to relative recovery rates from 83.07% to 106.3% at concentration levels in the range 100&ndash
200 &mu
g/kg. The within-laboratory reproducibility, expressed as a relative standard deviation, was &lt
15.5%. Decision limits ranged between 100.3 &mu
g/kg and 105.6 &mu
g/kg and the detection capability varied between 100.6 &mu
g/kg and 109.7 &mu
g/kg. Ruggedness was evaluated by following the Youden approach, in terms of milk mass, sorbent mass, centrifugation time, vortex time, type and volume of organic solvents and evaporation temperature.