An alternative derivatization reaction to the determination of doramectin in bovine milk using spectrofluorimetry.

The doramectin (DOR), which belongs to the avermectins group (AVM), has a high antiparasitic activity and so it has been widely used in food-producing animals. The DOR shows low fluorescence quantum efficiency and as a consequence, chemical derivatization reactions are necessary to produce derivatives with improved luminescent properties before its determination by fluorimetry. As the presence of this compound in food represents a risk to human health, an easy, clean and low cost derivatization reaction, which is alternative to those usually employed and that enables its spectrofluorimetric determination in milk samples, was developed. Ethanolic solutions of DOR, containing sodium hydroxide at a final concentration of 0.25 mol L(-1), after 60 min of heating at 50 °C, produced fluorescent signals 1000 times higher than the original ethanolic solution. Using these optimized conditions, a linear response range that extended from 50.00 to 1000 μg L(-1), with a value of (R(2)) equal to 0.9970, was obtained. Average recovery of DOR was 92.5±1.5% (n=3) in bovine milk fortified samples submitted to a liquid-liquid extraction at low temperature and pre concentration process, indicating the usefulness and effectiveness of the proposed method. The proposed spectrofluorimetric method is an alternative to high-performance liquid chromatography (HPLC) based methods, allowing rapid and simple detection of doramectin in milk samples.