Simultaneous analysis of kasugamycin and validamycin-A in fruits and vegetables using liquid chromatography-tandem mass spectrometry and consecutive solid-phase extraction

A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for simultaneous determination of two hydrophilic aminoglycosides, kasugamycin and validamycin-A, in a variety of matrices (apples, cabbage, cucumbers, lettuce, tomatoes, and eggplant) has been developed. The proposed method provides sufficient sensitivity and excellent chromatographic performance using a special ReproSil 100 C18 column with 0.1% formic acid as the mobile phase additive. Accurate mass information for both analytes was obtained based on time-of-flight (TOF) mass spectrometry. The methanol/water (70 : 30, v/v) with pH adjusted to 5.5 was selected as the extraction solvent. The combination of hydrophilic–hydrophobic-balanced (HLB) cartridges with strong cation exchange SCX cartridges was used to purify the extracts with strongly polar compounds and satisfactory results were obtained. The consecutive solid-phase extraction minimized signal suppression/enhancement which led to matrix effects in the range of −12.6 to 6.11% only. Recovery experiments were performed for both compounds at three levels (50, 100, and 500 μg kg−1) in six different matrices and yielded good recoveries ranging from 81.7% to 108% with relative standard deviation values below 13%. The limits of quantification (LOQs) for kasugamycin and validamycin-A were 4.1 μg kg−1 and 1.0 μg kg−1, respectively.