Matrix Recrystallization for MALDI-MS Imaging of Maize Lipids at High-Spatial Resolution

Abstract

Abstract. Matrix recrystallization is optimized and applied to improve lipid ion signals in maize embryos and leaves. A systematic study was performed varying solvent and incubation time. During this study, unexpected side reactions were found when methanol was used as a recrystallization solvent, resulting in the formation of a methyl ester of phosphatidic acid. Using an optimum recrystallization condition with isopropanol, there is no apparent delocalization demonstrated with a transmission electron microscopy (TEM) pattern and maize leaf images obtained at 10 μm spatial resolution.

High‐Spatial Resolution Mass Spectrometry Imaging: Toward Single Cell Metabolomics in Plant Tissues

“…We successfully applied this recrystallization strategy to plant tissues with DAN as a matrix and demonstrated no delocalization was present at 10 mm spatial resolution. [66] Recrystallization with 5 % isopropyl alcohol at 55 8C for 2 minutes was most optimal and increased ion signals by three times when applied to the imaging of maize leaves. More importantly, we found methanol was not a good recrystallization solvent due to side reactions with phosphatidic acids, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 indicating some care must be taken when using recrystallization methods.…”

“…It has been demonstrated that a recrystallization step can enhance the sensitivity of proteins without inducing delocalization of analytes, but this has been demonstrated only for animal tissues. We successfully applied this recrystallization strategy to plant tissues with DAN as a matrix and demonstrated no delocalization was present at 10 μm spatial resolution . Recrystallization with 5 % isopropyl alcohol at 55 °C for 2 minutes was most optimal and increased ion signals by three times when applied to the imaging of maize leaves.…”

Spatial distribution mapping of molecules in the grains of different rice landraces, using desorption electrospray ionization mass spectrometry

“…A study on maize embryo imaging by MALDI‐MS reported that the ions at m/z 685.4 and 709.4 are methyl phosphoesters of PA 34:2 ( m/z 671.4) and PA 36:4 ( m/z 695.4), respectively. It was also mentioned that the phosphoesterification of phosphatidic acid was detected only when 5% methanol was used as the solvent for matrix recrystallization …”

Improving the analyte ion signal in matrix‐assisted laser desorption/ionization imaging mass spectrometry via electrospray deposition by enhancing incorporation of the analyte in the matrix

“…Sublimation of the matrix onto the sample to be analyzed has been widely used, but typically requires a conditioning or recrystallization step to promote analyte incorporation . This conditioning has been performed with different solvents and parameters and shown to potentially introduce unexpected side reactions . Microspotting of matrices directly onto tissues has also been performed but results in a heterogeneous matrix overlayer as compared to those produced with sublimation or spraying of matrix solution …”

“…[22,23] This conditioning has been performed with different solvents and parameters and shown to potentially introduce unexpected side reactions. [24] Microspotting of matrices directly onto tissues has also been performed [25] but results in a heterogeneous matrix overlayer as compared to those produced with sublimation or spraying of matrix solution. [2] In the context of conventional MALDI sample preparation, electrospray deposition (ESD) has been shown to produce highly homogenous and reproducible samples.…”