Additional Methods of Sample Supply

Safety notice Unconventional sample supply techniques on commercial MALDI instruments require great care. Possible pitfalls include i) blocking of the vacuum lock due to unacceptable thickness of the target, ii) loss of the sample inside the ion source or inside the vacuum lock. Hi) damage to the instrument from electric discharges. 

Example I Polycyclic aromatic hydrocarbons (PAHs) are easily detected by LDI due to their strong UV absorbance. The positive-ion LDI-TOF mass spectrum of l,2,3,4,5,6-hexahydropheaianthro[l,10,9,8-up ra]perylene exclusively presents the molecular ion at m/z 356 (Fig. 11.16 for the El spectrum cf Chap. 5.2) [137]. 

Example II Fullerene soots as obtained by the Huffman-Kratschmer synthesis [140] can be characterized by positive- as well as negative-ion LDI-MS [135]. Such LDI spectra can exhibit fullerene molecular ion signals well beyond m/z 3000 among these, Ceo and are clearly accentuated (Fig. 11.17). Furthermore, such samples provide experimental carbon-only isotopic patterns over a wide mass range (Chap. 3.2.1). The spectrum below was obtained on a FT-ICR mass spectrometer hence the resolution is 175,000 at m/z 840, i.e., almost by a factor of 1000 higher than on early TOF instruments as used for the discovery of 

C ) and larger fullerenes [141]. The insets show expanded views of the ions for C ), C70, and C120 together with the corresponding calculated isotopic patterns. Note, that the accurate masses are lower than the nominal values by the mass of an electron, while the difference in mass of 1.0033 u between and can be recognized from the mass increment of the 1st and 2nd isotopic peaks. 

Note Normally, commercial MALDI instruments tolerate such a sample supply however, great care is recommended when performing this sort of experiments in order not to loose the sample inside the ion source or to damage the instrument s electronics from electric discharges. 

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