Identification and quantification method of spiramycin and tylosin in feedingstuffs with HPLC-UV/DAD at 1 ppm level

The use of the two macrolides antibiotics Spiramycin (S) and Tylosin (T) as growth promoters in animal feeding has been recently withdrawn in the European Union due to a concern about the outbreaks of farmacoresistance fenomena as a possible hazard for humans. For feed additives monitoring purposes, an analytical method has been developed for their extraction, purification and identification in different animal feedingstuffs (pelleted beef, pig, poultry feeds and calves milk replacer) at a minimum performance required limit (MRPL) of 1 microg g(-1) (ppm). Such limit has been established according to the lowest dosage of additives still able to elicit an appreciable growth promoting effect. Blank feeds were spiked at two concentration levels, 1.0 and 2.5 ppm in six replicates. After methanolic extraction, samples were cleaned up on SPE CN columns and extracts analysed in HPLC-UV/DAD, using a gradient elution. Detection limits, calculated as the tree time mean noise of 20 blank feeds, were 176 and 118 ng g(-1) for S and T, respectively. Results show good repeatability (CV% not exceeding the value of 15) and mean recovery in the range of 99-74% and 81-53% for S and T, respectively, at 1 ppm. When the standards were injected up to 250 ng the chromatographic method can resolve the components of analytes (Spiramycin I, II and III; Tylosin A and B) but can not resolve the components on real feed samples at the spiked levels considered. For this reason the identification and quantification of analytes on matrix were carried out considering the main compound of the drugs (Spiramycin I and Tylosin A). As a verification, the overlapping of UV spectra in the range 220-350 nm between analytical standards and the compounds in the matrix were considered.