Analytical Instrument Documents

MSTips No. 499

Mass spectrometry (MSI) technology using matrix-assisted laser desorption/ionization (MALDI) has been widely used in various fields in recent years. The MALDI method, which is a soft ionization method, can visualize the localization of various molecules. In a typical workflow of MALDI-MSI, a 5-10 μm thick tissue section is prepared and placed on a conductive ITO glass slide. A matrix is ​​uniformly applied on the slice, and MALDI-MSI measurement is performed. One of the challenges of MALDI-MSI is that it is difficult to prepare slices, such as the surface measurement of plants and plastic samples. In particular, fruits and plants contain a lot of water, making it challenging to prepare frozen tissue sections. For such samples, one solution is to transfer the organic compounds on the sample surface to a specially processed plate and measure them. This report used a novel, highly robust transfer plate, Poropare™ (Hamamatsu Photonics), to transfer compounds in strawberries and perform MSI measurement. Poropare™ is made by sintering glass beads of several tens of μm and depositing platinum on them to ensure electrical conductivity (Figure 1). This platinum effect also makes it possible to perform surface-assisted desorption ionization (SALDI-MSI) without a matrix. In this study, we examined both SALDI-MSI and MALDI-MSI. Furthermore, the high-mass resolution MALDI-TOFMS JMS-S3000 "SpiralTOF™-plus 3.0" used in this report employs a SpiralTOF ion optical system consisting of four electric sectors and has a long flight distance of 17 m. This makes it less susceptible to the unevenness of the Poropare™ surface, achieving high resolution. In addition, excluding post-source decay ions by the electric sectors allows for high-sensitivity measurements even in the low molecular weight region.