Abstract:

A method of high performance liquid chromatography-quadrupole/electrostatic field Orbitrap high resolution mass spectrometry (HPLC-Q/Orbitrap MS) was developed to determine fructo-oligosaccharides in milk powder. The milk powder samples were dissolved in deionized water. Subsequently, an aqueous solution of zinc acetate was used to precipitate protein. After centrifugation, the final aqueous solution was filtered by a polytetrafluoroethylene (PTFE) membrane with pore size of 0.22 μm. The analytes were separated on a Carbohydrate column (100 mm×2.1 mm, 2.6 μm) through gradient elution with the combination of acetonitrile and 0.1% formic acid aqueous solution. The target-MS/MS templates were performed at isolation window of m/z 4.0 and collision energy of 30 eV in positive mode to extract the accurate product ion mass of analytes. Under the optimal condition, 1-kestose (GF₂), nystose (GF₃) and 1-F-β-fructofuranosyl nystose (GF₄) were well separated and the accuracy of extracted mass routinely detected was below 5×10^-6 (5 ppm). The whole analysis time is only ten minutes. The detection limits for GF₂ and GF₃ were 100 μg/kg, and the detection limit for GF₄ was 55 μg/kg. Good linearities were obtained in their respective linear ranges with correlation coefficients higher than 0.998. The average recoveries at three spiked levels (5, 10 and 20 mg/kg) were in the range of 75.8%-107.3% and the relative standard deviations (RSDs) were in the range of 1.6%-8.3%. The proposed method is simple, sensitive, fast and only in need of precipitation of proteins. The interference of matrix can be eliminated through the selection of product ion. The results were convenient and reliable and thus can be used in the large batch determination of any milk powder.

Key words: fructo-oligosaccharides, high performance liquid chromatography-quadrupole/electrostatic field orbitrap mass spectrometry (HPLC-Q/Orbitrap MS), high resolution mass spectrometry (HRMS), milk powder