Analysis of oxytetracycline residue in salmon muscle using a portable analyzer based on EuIII luminescence

In the United States, oxytetracycline (OTC) was approved by the Food and Drug Administration (FDA) for use in salmon, catfish and lobster; worldwide, it is the most prominent therapeutant in aquaculture. In this study, OTC and 4-epiOTC residues in salmon muscle were determined using a portable analyzer based on europium-sensitized luminescence (ESL). Extraction was performed first in EDTA/metaphosphoric acid/NaCl/hexane and then in metaphosphoric acid. After centrifugation, cleanup was carried out using hydrophilic-lipophilic balance cartridges. The ESL intensity, integrated over a 25-1000 mu s interval, was linear (r(2) = 0.9999) over three orders of magnitude. In comparison to xenon flashlamp, light-emitting diode (LED) excitation reduced background noise by sixfold to 6.4 ng g(-1). Without prior chromatographic separation, this ESL method/instrument combination achieved 10.9 ng g(-1) limit of detection and <2% average relative standard deviation. Average recovery was 82.0, 83.6 and 86.8% at 50, 100 and 2000 ng g(-1), respectively.