I'm trying to get a molecular weight for my polymer which is supposedly composed of 200 glycerol monomethacrylate monomers (GMA) with molecular weight ~32K by using MALDI-MS. I'm not sure what conditions to use. I've tried dissolving the polymer in half DMSO and half THF/Acetone/Acetonitrile and then dissolving it with a matrix. I've tried DHB, Sinapinic acid, and CHCA but I'm getting nothing. In addition, I've tried to use linear positive/negative, reflector positive/negative modes but still getting no signal. Any recommendations? I've seen a lot of literature use IAA or dithranol for large molecular weights as the matrix but I currently do not have those.
Mr. Huyan,
YOu should spray the matrix over the sample, which should be preliminary placed over the MALDI sample holder.
Hi Frederick,
do you know the following links?
Article Matrix-assisted laser desorption/ionization mass spectrometr...
https://www.bruker.com/fileadmin/user_upload/8-PDF-Docs/Industries/MT-105-MALDI-CID_eBook.pdf
Article Use of MALDI-TOF to Measure Molecular Weight Distributions o...
Article Fragmentation behavior of poly(methyl methacrylate) during m...
http://etheses.dur.ac.uk/3962/
Article The effect of counter ions in matrix-assisted laser desorpti...
Regards
Markus
Hi Frederick,
First off, I would not attempt to run it in reflection mode until you get it to fly in linear mode. Typically molecules greater than 10 to 15K AMU do not retain they're structure as they decelerate and reaccelerate inside the reflector lens stack of the MS.
Second, I would start with this NIST web page which is their Polymer matrix recipe page, simple, but very useful. https://maldi.nist.govArticle Glossary of class names of polymers based on chemical struct...
Third, many polymers require a ionic species like sodium trifluoroacetate be added to the matrix which forms adducts that can then be ionized and detected by the MS. Matrix is the magic behind MALDI and is the most difficult part of getting successful analysis. Here is a paper that lays out some of the logic in picking a proper matrix. Article MALDI-TOF MS Analysis of Soluble PEG based Multi-step Synthe...
Four, polydisperse sample with a PD greater than 2 typically don't work well on MALDI, although this doesn't not seem like the issue with your sample.
Finally, if you are able to analyze it in linear then switch back to reflection mode to see if you can analyze it under higher resolution conditions. I do recommend trying both Positive and negative modes of operation, because some polymers can give an improved response in negative mode especially if they are more electronegative.
Hope this something here can help,
Ed
- Badges
- Science topic