Hello,
I did an enzymatic digest of alginate, an anionic polysaccharide from algae and performed MALDI-TOF. Now I have a chromatogram with several peaks but it do not know how to calculate the molecular weight of the oligosaccharides according to the peaks (relative intensity of m/z)?
I only know the molecular weight of certain oligosaccharides from alginate:
olgio MW
hepta-mannuronic / guluronic acid sodium salt 1404.76
hexa-mannuronic / guluronic acid sodium salt 1206.65
penta-mannuronic / guluronic acid sodium salt 1008.54
tetra-mannuronic / guluronic acid sodium salt 810.44
tri-mannuronic / guluronic acid sodium salt 612.33
di-mannuronic / guluronic acid sodium salt 414.23
mono-mannuronic / guluronic acid sodium salt 216.12
Example peak: 537.983 m/z. From this value the MW of Na+ must be withdrawed first, right?
Can someone help me?
Thanks!
There are a couple of things that are not clear here. How can you have a chromatogram that shows m/z in it? Do you mean total-ion chromatogram? (that's a bit of a misnomer, by the way) You probably have a spectrum where the oligosaccharides appear as several peaks, at different m/z values, due to multiple charges. Which immediately invalidates the above answer: if you have a mass of 100 and a charge of 1, you will see that ion at m/z 100, but if the charge is 2, you will see a peak at m/z 50 also, so worry very very much about your charge, because in your case it may show peaks at hundreds of Daltons mass difference, which are nonetheless related (originate from the same species). Here is a simple tutorial that helps you learn how to determine the multiplicity of the charge and hence the molecular mass (MS does not deal in weights): http://www.ionsource.com/tutorial/spectut/spec5.htm
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