Its logical that the calculated TOF will be constant among the samples prepared by the same method but that the calculated TOF will change by the preparation method. But I found that the TOF decreases by increasing the metal loading in the same method as the preparation. What does it mean? In another method of preparation, comparing both methods, we found that the TOF increases with increasing the metal loading. What does this mean?
I am not sure what you are asking, but I am guessing that your question is with regard to MALDI-TOF analysis. As you know, one generally mixes a small organic molecule, (the matrix), with the sample. The small organic molecule absorbs most of the energy of the laser while protecting the sample, and transfers it to the higher mass oligomer or polymer molecules that might otherwise be destroyed by the laser. The laser energy causes the sample to desorb from the solid into the gas phase and become charged, enabling its analysis by TOF-MS.
As a variation on this theme, certain metal salts can be used in place of small organic molecules in order to augment the efficiency of sample ionization:
http://www.sciencedirect.com/science/article/pii/S1044030598000385
The augmentation depends on the ratio of metal salt matrix to sample. I am not sure if that is the question that you are asking.
I don't think that you mean the following, but the thickness of the MALDI plate can affect the TOF measurements. Less thick plates will have longer TOF measurements. This can potentially shift peaks in the spectra and make it difficult to compare to other published results due to decrease in resolution or apparent mass.
My question is What does the increasing of TOF with the metal loading mean?
Hi, how are you calculating the number of active sites? A decrease in TOF can be found with an increased loading if you are expecting your number of active sites to keep increasing with loading. However, with higher metal loadings you can cause agglomeration, resulting in much larger particles which may or may not be active for your reaction. For example, if high energy sites like step and edges are the active sites, the proportion of these will continually decrease with larger particles and higher loadings. If your reaction proceeds on large flat terrace sites however, you would expect the number of active sites to increase with loading. Hope that helps.
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