Study of matrix effects for liquid chromatography–electrospray ionization tandem mass spectrometric analysis of 4 aminoglycosides residues in milk

• Matrix effect for aminoglycoside analysis in milk by LC–MS was explored.
• Consecutive SPE pretreatment was used to reduce matrix effect.
• Lower matrix effect was obtained by optimal strategies.

Matrix effect (ME) is always a major issue for the development of LC–MS/MS method. ME resulting from co-eluting residual matrix components can affect the ionization efficiency of target analytes, leading to quantification errors of the analytes of interest. The present work evaluates MEs of milk samples on simultaneous analysis of four aminoglycosides residues via LC–ESI/MS/MS including streptomycin, dihydrostreptomycin, spectinomycin and kanamycin. Approaches to reduce MEs were examined: optimization of the sample preparation, sample dilution and lower flow rate used. Three commercial sorbents were tested including Oasis MCX, Oasis HLB and Oasis WCX. WCX behaved better for all analytes, but high MEs (80.8–134.9%) were obtained. Therefore, a consecutive SPE of tC18-WCX was found to effectively reduce ME. Milk samples from different manufacturers were analyzed and low MEs (85.6–112.9%) were obtained.