Water for MALDI-ToF
Impact of Water
Although MALDI is more tolerant to contamination than other ionization methods, it is important to use reagents (e.g., matrix) and solvents of the highest purity so as to avoid making the analysis of the mass spectra more challenging than it already is.
- Ions
Ionic contamination, like Na+ and K+, will form adducts with the analytes and make data interpretation/analysis more challenging. Also, high salt concentration could affect crystallization of the matrix and analyte, leading to poor quality spectra.
- Organics
Some organics (detergents, polymers) could suppress the ionization of the analyte molecules. Detergents also disrupt the co-crystallization of matrix and analyte.
- Bacteria
Water for MALDI applications should be bacteria-free because they are sources of macromolecules (proteins, nucleic acids, carbohydrates) that could be detected by the mass spectrometer, complicating data analysis. They are also sources of ions and organics.
Experimental results
Figure 1 shows mass spectra of (A) cytochrome C, and (B) tryptic digest of bovine transferrin using a Bruker Autoflex MALDI-ToF instrument. Figure 2 was obtained in the reflectron mode. Ultrapure water from a Milli-Q® system was used to prepare the matrix. |
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Figure 1: MALDI-ToF spectra of (A) cytochrome C, and (B) tryptic digest of bovine transferrin using a Bruker Autoflex MALDI-ToF instrument. |
Figure 2: Obtained in the reflectron mode. |
Thus, even though MALDI ToF is known to be more tolerant than to ionic contamination compared to electrospray ionization, it is still important to use ultrapure water to obtain clean spectra.
More Information
- http://www.astbury.leeds.ac.uk/facil/MStut/mstutorial.htm
- http://www.molecularstation.com/forum/mass-spectrometry-forum/1614-mass-spectrometry-tutorial-video.html
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