MALDI Imaging SpiralTOF™-plus

MALDI MS imaging was initially developed to focus on high molecular weight compounds such as proteins and peptides. However, with the expanding applications of MALDI MS imaging, the interests have shifted to include smaller molecules such as lipids, pharmaceuticals, and pharmaceutical metabolites. Conventional MALDI-reflectron TOFMS has difficulty discerning small molecule signals from those of matrix. In the case of MALDI MS imaging, signals from unwanted molecules on the specimen surface will often interfere with signals from the target analytes. High selectivity by means of high mass-resolving power is essential for obtaining reliable target analyte spatial distributions.

The SpiralTOF™-plus with its high mass-resolving power is indispensable for MALDI MS imaging.

Above: A tissue section is placed on an ITO-coated glass slide, and matrix solution is sprayed onto the surface.

A special target plate for thick specimens is available as an option. The specimen is moved beneath the focused laser beam to create a time dependent series of mass spectra where each time corresponds to a specific spatial location. Analysis of the data allows the researcher to visualize the spatial distribution of specific compounds on the sample surface. Mass spectrometry imaging data can be analyzed with the JEOL msMicroImager™ software or converted to a common data format imzML which allows data analysis by third party software such as BioMap.

Mouse brain sections contain a variety of lipid classes. A mass spectrum obtained from the tissue section is highly complex, especially in the region of m/z 700 - 1,000. Many of the peaks in the mass spectrum are less than 10% of the base peak, representing minor components. MALDI MS imaging of lipids requires a mass-resolving power high enough to separate the minor peaks from interferences. The bottom mass spectrum below shows the expansion of m/z 820 - 823. Many peaks were separated from each other by less than 0.1 u. The high mass resolving power of the SpiralTOF™-plus clearly separated these isobaric peaks, thus allowing the elucidation of 4 lipid elemental compositions. Moreover, each lipid clearly showed a different spatial distribution. Elucidation of elemental compositions and accurate determination of spatial distributions for each lipid would be difficult with a conventional reflectron TOFMS with moderate mass-resolving power.

The data were acquired in a joint research project with the Mass Spectrometry Group, Project Research Center for Fundamental Sciences, Graduate School of Science, Osaka University.

The tissue section specimen was provided by Awazu laboratory, Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University.

Advanced statistical data analysis was performed based on all of the mass spectral peaks detected in the data above by using SCiLS Lab MVS. Segmentation of the characteristic regions and extraction of the mass spectrum from each segment facilitated by the high mass-resolving power of the JMS-S3000 SpiralTOF™-plus have been achieved. Download the Brochure for licensing details.

Result of pLSA (probabilistic latent semantic analysis)

Segmentation

Relationship between pLSA score plot and Segmentation

Mass spectra from respective segments. Analyzed with SCiLS Lab MVS, Version 2020b Premium3D.

In conventional MS imaging, a MS image is extracted by specifying a specific m/z range. However, since polymers are polydisperse and have molecular weight distributions, the conventional method can generate only a mass image of a specific degree of polymerization, and the spatial distribution of the polymer as a whole cannot be visualized. To solve this problem, msMicroImager™ can generate an image with the number average molecular weight (Mn), weight average molecular weight (Mw), and polydispersity (D) of the polymer. This makes it possible to visualize the spatial distribution of polymers more intuitively by consolidating hundreds of mass images derived from each degree of polymerization / isotope peak into three images.

A conventional method can visualize the distribution of a polymer species with a specific degree of polymerization.

Also see: MSTips No. 305.