Matrix-Free Assisted Laser Desorption Ionization Using Metal-Organic Frameworks

Army Research, Development and Engineering Command, Aberdeen Proving Ground, Maryland

Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique that is widely applied in the characterization of large biomolecules using various mass spectrometry (MS) analyzers, specifically, time-of-flight (TOF) analyzers. The MALDI process involves the deposition of an analyte solution onto a metal substrate before the addition of a matrix. The matrix/analyte dry spot is exposed to a UV laser, and the laser energy that is absorbed by the matrix/analyte is converted into heat energy that initiates charge transfer, which results in the desorption of the matrix and analyte molecules in ionized form. The positive ions are then accelerated through a vacuum into MS analyses.

The MALDI process, however, lacks guiding systematic principles, which has resulted in mostly empirical work. For example, there is no universal matrix that can be used in the MALDI-MS analysis of biomolecules. Hundreds of compounds were assessed with several analytes and were given qualitative ratings. These variables were the products of differences in charge transfer efficiency between the matrix and analytes because of chemical and structural factors.