MALDI-TOF imaging mass spectrometry of artifacts in "dried droplet" polymer samples.

Matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) imaging of polystyrenes with various molecular masses was applied to study spatial molecular mass distribution of polymers in sample spots prepared by the "dried droplet" method. When different solvents and target surfaces were examined, a segregation of single homologous polymers was observed depending upon the evaporation rate of the solvent. For the observed patterns left by the evaporating droplet, a hypothesis is offered taking into account different hydrodynamic interactions and diffusion. The results illustrate that spot preparation using the conventionally "dried droplet" method is prone to artifacts and should be avoided for reliable and reproducible MALDI mass spectrometry experiments with regards to the determination of molecular masses and mass distributions.