Spatial visualization of molecular information on a tissue is of great interest in biomedical research and mass spectrometric imaging can provide that spatially defined information on plant or animal tissue. Mass spectrometry is an appealing imaging technique as it enables simultaneous detection of a large range of compounds without any labeling needs.
Direct profiling of tissue sections by MALDI mass spectrometry, using mass spectrometry imaging, is a powerful technique to study the spatial distribution of large and small molecules directly from a tissue sample. Illustration of mass spectral data as two-dimensional images allows the visualization of spatially distributed molecules.
Highly complex data generated during a MALDI imaging experiment can be processed using Waters High Definition Imaging (HDI), an intuitive informatics solution for simplified and streamlined mass spectral imaging workflow. The HDI software package contains all the data analysis and statistical tools required for a rapid and effective interrogation of a complex imaging data. For example, molecular ions directly corelated to a target compound can be easily identified.
Conventional MALDI Imaging
A limitation of an imaging experiment by a conventional MALDI MS is the absence of a separation step prior to the mass spectrometric detection. A tissue sample has tremendous chemical complexity and often posses a risk of isobaric ion interference during a mass spectrometric imaging analysis. This can very easily result in an inaccurate interpretation of the data and subsequently the biological mechanism. High Definition Imaging with ion mobility allows the separation of ions in gas phase and removes isobaric interference for a more accurate and confident data.
High Definition Imaging with Ion Mobility
The extra dimension of separation provided by ion mobility on MALDI SYNAPT HDMS System can be used to produce images without interference from background ions of similar mass, leading to more precise localization of a drug or metabolite of interest. Ions are separated using ion mobility (IMS) prior to mass analysis.
An example of filtering out interfering ion is shown using the MALDI HDMS Imaging of a kidney cross section. The use of HDMS clearly helps to provide the true spatial tissue distribution of the endogenous metabolite of mass 402.012 Da by removing intensity contribution due the interfering matrix ion of mass 402.072 Da.
Ion image of m/z 402.012, without ion mobility separation.
Ion image of m/z 402.012 (ion of interest) with ion mobility separation. Ion mobility significantly lower background noise level by filtering out the isobaric interference.
Ion image of m/z 402.07 (interfering background ion) with ion mobility separation.