The confirmation and quantification of selected aminoglycoside residues in animal tissue and bovine milk by liquid chromatography tandem mass spectrometry

Aminoglycosides are a large class of antibiotics that are characterised by two or more amino sugars linked by glycosidic bonds to an aminocyclitol component. They are water soluble, highly polar thermally labile compounds with no chromophores or fluorophores and so difficult to assay using standard HPLC, GC or GC-MS instrumentation. This paper reports a robust method to confirm and quantify the levels of dihydrostreptomycin, streptomycin, apramycin, neomycin and gentamicin (C1, C2 and C1a) present in animal tissue and dihydrostreptomycin, streptomycin, neomycin and gentamicin (C1, C2 and C1a) present in bovine milk using liquid chromatography-tandem mass spectrometry. The aminoglycosides were extracted from the samples with perchloric acid, EDTA, phosphate buffer solution, followed by centrifugation and cleanup using weak cation exchange solid phase chromatography. The compounds were separated with a 5 μm C18 HPLC column and a mobile phase consisting of a mixture of acetonitrile, water and 50 mM heptafluorobutyric acid. Matrix matched standards were used to achieve the best accuracy of the method. The Limits of Quantification (LOQ) (0.1-0.5 mg/kg for animal tissue and 0.01-0.1 mg/kg for milk) were based on the requirements of the Australian antibiotic residue monitoring programs. The method was used to measure the levels of aminoglycoside residues in samples submitted by the Australian Regulatory Authorities.