Table 2. Summary of the Fragmentation Rules and Diagnostic m/z Values for Keratan Sulfates.
MSn Stage | Fragmentation Rule | Diagnostic m/z |
---|---|---|
MS1 | Molecular ion ([M-nH]n−) is given without considerable loss of sulfate. | |
The number of sulfate and/or carboxylate (n), as well as molecular weight (M) is determinable. | ||
MS2 (on [M-nH]n−) | Dehydration ([M-H2O-nH]n−) and 0,2Ar cleavage occur in most oligosaccharides. | |
The dehydration is ascertained to take place between C-2 and C-3 of reducing GlcNAc. | ||
Desialylation occurs preferentially in sialylated oligosaccharides. | m/z 290 | |
MS3 (on [M-H2O- nH]n−) |
[Y1 - H2O - OSO3H]− ion is detected for GlcNAc6S at reducing end. | m/z 184 |
B1 ion is detected for Gal6S at nonreducing end. | m/z 241 | |
MS3 (on 0,2Ar) | 2,4Ar ion appears intensely (except for L2 and SL1). | |
[OCHCH2OSO3]− ion is detected for 6S at reducing end. | m/z 139 | |
[0,2Ar-H2O]n− ion is detected for Gal-GlcNAc6S (L2) sequence at reducing end. | ||
MS4 (on 2,4Ar) | Extensive fragment ions resulting from glycosidic cleavages are obtained, which give valuable information for sequence determination. |
|
B1 ion is detected for GlcNAc6S or Ga16S at nonreducing end. |
m/z 282 (GlcNAc6S) m/z 241 (Gal6S) |
|
B2 ion is detected for monosulfated disaccharide sequence at nonreducing end. | m/z 444 | |
Doubly charged B2 ion is detected for disulfated disaccharide sequence at nonreducing end. | m/z 261.5 | |
Y2 ion is detected for Gal6S-GlcNAc6S (L4) sequence at reducing end. | m/z 301 | |
[OSO3H]- and/or [2,4Ar-OSO3H]n− ions are detected for Gal6S at any position in the sequence. | m/z 97 |