Homogenous dispersive solid phase extraction combined with ionic liquid based-dispersive liquid–liquid microextraction of gentamicin and streptomycin from milk prior to HPLC-MS/MS analysis

Abstract

A salt-induced homogenous dispersive solid phase extraction method combined with an ionic liquid based-dispersive liquid–liquid microextraction was developed for the extraction of two aminoglycoside antibiotics (gentamicin and streptomycin) form milk samples prior to their determination by high performance liquid chromatography-tandem mass spectrometry. For this purpose, 15 mL milk sample mixed with 300 mg trichloroacetic acid to precipitate the sample proteins. After vortexing (1 min) and centrifugation (for 3 min at 5000 rpm), the supernatant was transferred into another test tube. After adjusting the solution pH at 10, polyvinylpyrrolidone (75 mg) was dissolved in it. The homogenous phase was broken by adding sodium chloride (20%, w/v) and polyvinylpyrrolidone was precipitated as fine particles which acted as a sorbent. After centrifugation, the supernatant phase was discarded and the analytes were eluted from the sorbent surface using 1.25 mL methanol. Subsequently, methanol was mixed with 85 µL trihexyl(tetradecyl)phosphonium chloride and the mixture was quickly injected into sodium chloride solution (10%, w/v). After a few seconds, the extraction solvent collected on the top of the solution was used in determination of the analytes. Under optimal conditions calibration curves of the analytes were linear in the range of 1–500 ng mL⁻¹. Also, limits of detection and quantification were 0.29 and 0.18 ng mL⁻¹; and 1.0 and 0.61 ng mL⁻¹ for gentamicin and streptomycin, respectively. The extraction recoveries were 87 and 93% for gentamicin and streptomycin, respectively. Acceptable relative standard deviations ≤ 6.1% were also obtained. At last, the studied antibiotics were successfully determined in milk samples.