MALDI TOF mass spectrometry for the characterization of phosphorus-containing dendrimers. Scope and limitations

Neutral phosphorus-containing dendrimers with aldehyde groups at the periph ery have been analyzed using matrix-assisted laser desorption ionization ti me-of-flight mass spectrometry (MALDI-TOFMS) up to generation four, Althoug h the expected quasi-molecular ion is generally observed, the mass spectral pattern, presence of fragments and adducts related to the original skeleto n, is highly relevant to the sample preparation (nature of the matrix: 2-5- dihydroxybenzoic acid(2.5-DHB), 1,8-dihydroxy-9[10H]-anthracenone (dithrano l), 6-azathiothymine, 2,4,6-trihydroxyacetophenon, 7-hydroxycoumarin or 2-a nthramine, and addition of alkali metal salts). The dithranol matrix with a ddition of LiI offers milder:conditions; however, abundant fragments are st ill observed for the higher generation dendrimers, Investigation of these e ffects in connection with SEC, NIMR, and MALDI-TOFMS studies of UV preirrad iated dendrimers allows the assumption to be made that fragmentation occurs in MALDI due to the relatively strong absorption of the dendrimers at 337 mn. Fragmentations and formation of adducts involve nitrogen-nitrogen bond cleavage, imine metathesis, and reaction of aldehyde groups with internal i mino groups.