Abstract
Oxytetracycline (OTC) residue in honey is detected using a portable analyzer designed to specifically target tetracycline (TC) drugs based on europium-sensitized luminescence (ESL). A 385 nm light emitting diode (LED) is used as the excitation source and a photomultiplier tube as the light detector. OTC is extracted from honey and cleaned up by solid phase extraction (SPE) using Strata X-WC weak cation exchange cartridges. To the eluate Eu(III) is added to form a Eu-TC chelate at pH 8.5. Efficient intrachelate energy transfer allows sensitive OTC detection at λ<sub>ex</sub>=385 nm and λ<sub>em</sub>=610 nm. After a 25-µs time delay, the ESL signal is integrated over a 25-1000 µs interval. The signal intensity reveals a linear relationship (R<sup>2</sup>=0.972) to OTC concentrations in the 10-200 ng/g range. The limit-of-detection is 6.7 ng/g with an average 5.8% relative standard deviation. The background signal corresponds to ~10 ppb. This instrumentation and method combination enables field analysis that is especially useful for beekeeping industry.
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