Laser desorption and ionization time-of-flight versus matrix-assisted laser desorption and ionization time-of-flight mass spectrometry of Pt(II) and Ru(III) metal complexes

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been recently established as a powerful, soft ionization technique for the analysis of both transition metal complexes, which are used as metallo-drugs in the therapy of various types of tumors, and biomolecules. Since some metal complexes absorb light in the UV range, it should be possible to analyse them without additional matrices, i.e. using LDI-TOF MS. In this study, the matrix-free approach was tested for the analysis of [PtCl2(dach)] (dichloride(1,2-diamincyclohexane) platinum(II)), [RuCl2(en)(2)]Cl (dichloridobis(ethylenediamine) ruthenium(III) chloride) and [RuCl2(bipy)(2)]Cl (bis(bipyridine)dichloridoruthenium(III) chloride) and the detection limit for these compounds was determined. In summary, the LDI-TOF mass spectra of [PtCl2(dach)] and [RuCl2(en)(2)]Cl are rather simple, whereas in the presence of 2,5-DHB as a matrix, additional peaks are generated. On the other hand, the standard MALDI-TOF mass spectrum of [RuCl2(bipy)(2)]Cl exhibits only one peak arising from the complex, in contrast to six peaks detectable in the LDI-TOF mass spectrum. The detection limit in the MALDI-TOF MS analysis of [PtCl2(dach)] and [RuCl2(bipy)(2)]Cl complexes was lower than that determined in LDI-TOF MS. Taking all into account, in this paper, we have demonstrated some advantages and drawbacks of the matrix-free LDI-TOF mass spectrometric analysis of transition metal complexes.