Determination of residual oxytetracycline in honey with an immunoassay kit

Abstract - The application of the ELISA kit Ridascreen 'Tetracyclins' (from R-Biopharm GmbH, Darmstadt, Germany) for the semiquantitative analysis of oxytetracycline (OTC) residues in honey samples was investigated. To assess the extension of the kit to this use, some OTC-positive honey samples, spiked with OTC at concentrations ranging from 2 to 250 ppb, were prepared, purified and submitted to the ELISA test. For every set of positive honey samples, a set of OTC-standard solutions in water at the same concentration value of the positive samples and an OTC-negative (blank) control honey sample, were tested. Also, the efficiency of three different chemical purification procedures of honey samples was studied and verified: (1) the honey samples were diluted in water; (2) the honey samples were purified on a prepacked reversed-phase column (C-18 cartridges); (3) the honey samples were purified by a two-step system using a C-18 cartridge and a Diol-column. The mean recoveries of OTC were 90.4% (CV = 2.6%) for the test using C-18 (2) and 88.6% (CV = 2.1 %) for the test using both C-18 and Diol cartridges (3). The detection limits were lower than 50 ppb.