Matrix-assisted Laser Desorption/Ionization-Mass Spectrometry Imaging of Oligosaccharides in Soybean and Bean Leaf with Ionic Liquid as Matrix

Abstract

Abstract The ionic liquid butylamine 2,5-dihydroxybenzoate (DHB-BuN) was chosen as the matrix for improving reproducibility of oligosaccharides quantification, and imaging oligosaccharides in soybean and leaf by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). In the experiment, ionic liquid matrix of methanol solution (20%, V/V) was simply covered onto the sample slice, and MS imaging experiment was thus performed to analyze oligosaccharides and their distribution in soybean and soybean leaf in positive ion mode with laser power of 70%. As a result, the MALDI-MS analysis of three oligosaccharides including sucrose, raffinose and stachyose was performed using the ionic liquid matrix, and the reproducibility RSD was less than 3% for in-spot and less than 4% for spot-to-spot. The linear correlation coefficients (R2) of standard curves between MS peak intensity and oligosaccharides concentrations raging from 0.062 mg mL−1 to 1.00 mg mL−1 were all no less than 0.996, which showed a great potential in quantitative analysis of oligosaccharides by MALDI-MS. The matrix was then used for the imaging analysis of disaccharide, trisaccharide and tetrasaccharide on the surfaces of soybean chip and soybean leaf by MALDI-MS, and the mass spectrometric imaging of the three kinds of oligosaccharides was obtained with a spatial resolution of 150 μm. The result indicated that the distribution of three kinds of oligosaccharides in the soybean was roughly homogeneous, and mostly at its tip part in the leaf. The contents of the three oligosaccharides could be estimated by their MS peak intensity and above standard curve. This study suggested that the ionic liquid DHB-BuN matrix could be well applied in MALDI-MS imaging analysis of oligosaccharides in different samples.