Determination of tobramycin in serum using liquid chromatography–tandem mass spectrometry and comparison with a fluorescence polarisation assay

We have developed a tandem mass spectrometry (LC–MS–MS) method for measuring tobramycin concentrations in serum samples and have compared it with a fluorescence polarisation immunoassay. After protein precipitation with acetonitrile supernatant was injected into the LC–MS–MS system. A C18 cartridge (4×2 mm) was eluted with a step gradient of 20–100% methanol containing HFBA. The retention times were, tobramycin 1.05 min and sisomycin 1.05 min. The MRM transitions were: m/z 467.8>163 (tobramycin) and m/z 447.8>160 (sisomycin). The limit of quantification was 0.15 mg/l and the assay was linear up to 50 mg/l. Assay precision was <6% within and between batch.