Degradation of oxytetracycline in honey as measured by fluorescence and liquid chromatographic assays

Abstract - Federal regulations in many countries do not permit residues of oxytetracycline (OTC) in marketable honey. At or near the low limit of detection by fluorescence assay we have found that unforeseen nectar sources could lead to false positive readings. In an effort to maximize sensitivity and increase confidence in detecting trace amounts of OTC in samples of honey, a rapid HPLC isocratic method has been developed that uses a poly(styrene-60% divinylbenzene) column (Polymer Labs, PLRP-S). Honey is diluted 1:4 with 0.1 N hydrochloric acid and a 200-μl aliquot of the diluted honey sample is injected. The utility of the method was demonstrated by medicating research colonies of the honey bee, Apis mellifera, with OTC and analyzing the honey stored by the foraging bees. Both fluorescence assay and HPLC methods proved suitable for determining the stability of oxytetracycline in aqueous solutions and in honey stored at various temperatures. Between 0.5-50 ppm of OTC in research samples of honey can be determined within 15 min by the new HPLC method described.