Matrix ions as internal standard for high mass accuracy MALDI mass spectrometry imaging

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Treu, Axel ; Römpp, Andreas:
Matrix ions as internal standard for high mass accuracy MALDI mass spectrometry imaging.
In: Rapid Communications in Mass Spectrometry. Bd. 35 (20 April 2021) Heft 16 . - No. e9110.
ISSN 1097-0231
DOI der Verlagsversion: https://doi.org/10.1002/rcm.9110

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Abstract

Rationale High mass accuracy is indispensable for reliable identification in MALDI mass spectrometry (imaging). Ubiquitous matrix ions can serve as reference masses for mass calibration, if their sum formula is known. Here we report an overview of ions generated on tissue by eleven common MALDI matrices for use in internal or external mass calibration. Methods Matrices covered in this study were applied onto coronal mouse brain sections using a pneumatic sprayer setup. MALDI imaging was performed on a Q Exactive HF orbital trapping mass spectrometer coupled to an AP‐SMALDI 10 source. Measurements were conducted with high mass resolution (240k FWHM @ m/z 200) and high mass accuracy with an RMSE of better than 1.5 ppm achieved via internal mass calibration using matrix ions. Results MALDI MS imaging was used to investigate ions generated on tissue by eleven common MALDI matrices. An example of using matrix ions for internal mass calibration in MALDI imaging of drug substances and lipids in murine lung sections is presented. Tables containing the cluster composition, sum formulas as well as the measured and theoretical m/z ratios of the identified ions were compiled for each matrix. Conclusion Using matrix ions as reference masses for internal and external mass calibration in MALDI MS imaging is an effective and elegant way to achieve sub ppm mass accuracy as it makes use of ubiquitous signals present in every MALDI MS spectrum without the need for an additional calibration standard.