Aminoglycosides are widely applied antimicrobial drugs in current veterinary practice. In the U.S., USDA Food Safety and Inspection Service (FSIS) uses a semi-quantitative microbial assay to determine violative levels of aminoglycosides (and some other antibiotics) in animal tissues.
For positive findings, this assay is followed by a confirmatory LC-MS/MS method based on a laborious sample preparation using cartridge-based solid-phase extraction (SPE). The aim of this study was to develop a streamlined approach for
multiresidue LC-MS/MS analysis of aminoglycosides that would provide fast screening and eliminate the microbial assay and the cartridge-based SPE and evaporation steps. The streamlined sample preparation method involves buffer extraction, followed by a disposable pipette extraction (DPX)
with a weak cation exchange sorbent. The DPX technique uses disposable pipette tips with a small amount of loosely contained sorbent material that is mixed with the sample solution. DPX speeds the SPE process, reduces material cost and solvent use, and enables easy automation. After elution from the DPX tip, twelve target aminoglycosides are analyzed
in ESI positive mode using a fast UPLC-MS/MS method, which employs an ion-pairing agent to retain highly polar aminoglycosides on a reversed-phase column BEH C18 (50 x 2.1 mm, 1.7 µm). During the LC-MS/MS method development,
various aqueous normal-phase chromatography conditions were also tested for LC separation of aminoglycosides using different column chemistries (hydride-based silica bonded C18 and hydrophilic interaction LC, HILIC, columns), dimensions, and mobile phase compositions.