Ionic Liquid As Matrix And Ultrasonic Spray As Matrix Deposition Method For MALDI-MS Imaging Analysis

Matrix-assisted laser desorption/ionization-mass spectrometric imaging?MALDI-MSI?technique provides an extremely powerful tool for the investigation of the compositional distribution in tissues or different tissue states in situ.Through image construction software,MALDI-MSI of tissue section provids"direct"analysis and visualizes tissue distribution information for a wide variety of compounds at the molecular level,and obtains their in situ localization,qualitative and quantitative information of the target components in the tissue.The selection matrix and its deposition way are important to MALDI-MSI research.In the thesis,using FT-ICR-MALDI-MS instrument,we studied the matrix and matrix deposition methods.Ionic liquid as matrix and ultrasonic spray as matrix deposition method are presented to improve uneven distribution of matrix and poor reproducibility encountered in MALDI-MS imaging.?1?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 laserdesorption/ionization-mass spectrometry?MALDI-MS?.In the experiment,ionic liquid matrix was simply covered onto the sample slice using its methanol solution?20%,V/V?,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 the 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^–1were 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?m.The result indicated that the distribution of the three kinds of oligosaccharides was roughly homogeneous in soybean,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.?2?Ultrasonic spraying as matrix deposition method was built and applied in MALDI-MSI using a simple device to obtain micron-sized small cocrystallisation.In the experiment,After comparing seven different matrices,we selected DCTB as a suitable matrix for the detection of triacylglycerol?TAGs?and phosphatidylcholines?PCs?.The DCTB matrices was deposited on the surface of corn sections by the ultrasonic spraying device.By optimizing experimental conditions,the corn sections were then analysed by MALDI-MS using positive ion mode.The simultaneous analysis result of MALDI-MSI obtained more than16 molecules in corn,including TAGs and PCs.The result demonstrated that ultrasonic spraying enables the deposition of small volumes of MALDI matrix solution and provides satisfactory reproducibility and homogeneous matrix crystallisation.