Hi, I am trying to analyze a protein via MALDI and I'm having trouble getting a spectrum of it. I'm limited to using positive ion mode. The protein is highly negative (charge of -67 @ pH 7) and it's pI=3.94. I suspect that acidic matrix solution (50/50 MeCN:H2O, 0.1% TFA, and sinapinic acid) is causing precipitation of the protein and thus the vacuum sucks up the precipitated analyte. Is there a way to run MALDI on the sample in a more basic matrix. Your time and advice would be much appreciated!
You might try prespotting the matrix only to create the dry MALDI matrix spot, then overlay the protein solution in as dilute a buffer as possible. Let that dry. This will often work, but if you mix the prespotted matrix with the overlay using a drop of acetone after everything in dry, you can sometimes get better results.
Mr. Fox,
Please, consider sample preparation methods for solids by MALDI in work [1].
Importantly, there has been shown a new quantification method for analysis of MS intensity together with quantitative correlations between experimental MS parameter ''intensity'' and 3D structures of the analytes.
Work [2] demonstrates the same quantitative method applied to ESI-MS spectra of oligopeptides in solution. The analysis of these objects is directly applicable to analysis of proteins.
In other words, the quantitative method described in [1,2] - it is our development -is applicable to MALDI and ESI MS results, i.e. to condense phase analyses.
[1] https://www.grin.com/document/425061
[2] Stochastic dynamic electrospray ionization mass spectrometric diffusion parameters and 3D structural analysis of coordination species of copper(II) ion with glycylhomopentapeptide and its dimeric associates, Journal of Molecular Liquids, 282, 2019, 70-87, Bojidarka Ivanova, Michael Spiteller
Luke V Schneider , thank you for your suggestion. I will definitely give it a shot.
Bojidarka B. Ivanova, thanks for the articles that you recommended. I will check them out.
Hi Dr. Luke V Schneider , I tried what you recommended, but to no avail. I added 2uL of matrix to the plate and allowed it to dry. I then overlayed 1 uL of 30 uM protein analyte (3 mM HEPES, 42 mM NaCl, pH 7.4) and allowed to dry. I also tried adding 1 uL of acetone on top after the matrix and sample were dry. Just wanted to confirm that I executed your suggestion properly.
Try removing the NaCl. You might also try pyridinium acetate as the buffer
I really do appreciate these pointers. I will give it another shot considering what you’ve said. And Yes, I’m using TOF-TOF. Once again, thank you for your time.
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