Laser desorption/ionization mass spectrometry of peptides and proteins with particle suspension matrixes

Systematic investigations of particle suspensions for the laser desorption/ ionization of peptides and proteins are presented. The performance and suit ability for time-of-flight mass spectrometry of different particle material s and sizes, suspended in a variety of different liquids, are described. Pe rformance characteristics such as accessible mass range, achievable mass re solution, analytical sensitivity, and fragmentation are reported. For the d esorption of peptides and small proteins, nanoparticle suspensions in glyce rol were found to perform comparably to UV-MALDI-MS with common "chemical" matrixes. For proteins in the mass range of similar to 12-30 kDa, mass reso lution and analytical sensitivity decrease sizeably; for proteins with mass es in excess of similar to 30 kDa, no spectra could be recorded with any of the tested particle/liquid combinations. The results were found to be larg ely independent of the laser wavelength in the range from the near-UV to th e near-IF because of the strong particle absorption throughout this wavelen gth range. Ions are shown to originate predominantly from analyte molecules adsorbed at the particle surface, Nanoparticles with a diameter of a few n anometers were found to be superior to microparticles of similar to 1 mu m diameter or above. Thermodynamic modeling suggests that this different beha vior is caused by the different achieved peak temperatures of the two parti cle sizes.