Stephane Mouradian, Christine M. Nelson and Lloyd M. Smith
University of Wisconsin,Department of Chemistry, Madison, WI 53706
MALDI Mass Spectrometry has brought significant advances in the analysis of large biopolymers. However, the desorption/ionization mechanism remains unclear and the particular influence of the crystal formation process has yet to be understood. In this work, we replace the usual matrix crystals by a monolayer of a highly absorbing matrix-like chemical which is covalently linked to a gold surface. In this experiment, analytes such as proteins or oligonucleotides are directly deposited on the covalently modified probe tips. The samples are irradiated at 355nm and the molecular ions are detected using a Time of Flight Mass Spectrometer (TOFMS). Several types of monolayers have been investigated and tested for their ability to produce molecular ions in the positive and negative ion modes. dT10 oligonucleotide and proteins as large as cytochrome C were successfully analyzed using this procedure. As a control, no molecular ion was detected when the analyte was deposited onto a clean bare gold surface. By further characterizing the monolayers used in this type of experiment, we expect to gain a better understanding of the mechanism of production of molecular ions in MALDI.
This work was supported by Department of Energy Human Genome grant DE-FG02-9lER61130