Innovative mixture of salts in the quick, easy, cheap, effective, rugged, and safe method for the extraction of residual macrolides in milk followed by analysis with liquid chromatography and tandem mass spectrometry.

A simple extraction technique has been developed for seven macrolide antibiotics in milk. The procedure involves a modified quick, easy, cheap, effective, rugged, and safe method based on acetonitrile extraction, followed by the addition of a mixture of salts (sodium sulfate, sodium chloride, and potassium carbonate) not yet reported in literature. The method was validated for tylosin and was selective, free of matrix effect, and linear in the range of 0.78-18.75 ng/mL in the final extract, corresponding to 0.125-3 times the maximum residue limit. The limit of detection, limit of quantification, decision limit, and detection capability were, respectively, 0.84, 2.79, 58.4, and 71.7 μg/kg. The overall average recovery at 25, 50, and 75 μg/kg ranged from 89-97%. Repeatability and intermediate precision expressed by relative standard deviations were below 10.5 and 12%, respectively. The extension of the validation for spiramycin, throleandomycin, oleandomycin, roxithromycin, erythromycin, and clarithromycin is under consideration since the procedure proved to be able to efficiently extract all studied macrolides, with recoveries from 74-104% at 50 μg/kg for tylosin, erythromycin, spiramycin, and oleandomycin and 20 μg/kg for throleandomycin, roxithromycin, and clarithromycin.