N
X
C
Hal
O
N
S
P Si
Natural
Products
Solvents
C
C
C
C C
C
8.13 Spectra of Solvents and References
441
8.13.3 Spectra of Common MALDI MS Matrix Compounds
Matrix-assisted laser desorption ionization (MALDI) mass spectra (MS) usually
show signals for protonated or deprotonated molecular ions, [M±H] ± , and protonated
clusters, [M n +X m ±H] ± (n, m = 0, 1, 2, …), of the sample and matrix molecules, X.
In positive ionization mass spectra, clusters of the type [M n +X m +metal cation] +
occur even if there are only traces of metal salts in the sample. Sodium (23 u) and
potassium (39 u) ion adducts are often encountered. The nature of the clusters is
revealed by the regular intervals at which their signals occur in the spectra [4].
Matrix Compounds in Positive Ionization MALDI Mass Spectra
3-Aminoquinoline (M r 144.2)
α-Cyano-4-hydroxycinnamic acid (M r 189.2; m/z 212, [M+Na] + )
2,5-Dihydroxybenzoic acid (M r 154.1; m/z 177, [M+Na] + ; m/z 193, [M+K] + )
2,6-Dihydroxyacetophenone (M r 152.1; m/z 175, [M+Na] + ; m/z 191, [M+K] + ; m/z
365, [2M+Na+K-H] + ?)
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
50
0
145
289
433
N
NH 2
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
50
0
102
190
212
379
COOH
CN
HO
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
50
0
23
39
137
155
177
193 273 288
HO
OH
COOH
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
50
0
23 39
153
175
191
365
HO O
OH