  Matrix Assisted Laser Desorption Ionization (MALDI) is a soft ionization
method that finds widespread applications in high-throughput mass spectrometric
analysis. One of the main limit of this technique is that it requires the use
of matrices: these molecules enable the analytes desorption and ionization
(D/I) processes but also generate strong interfering signals in the low mass
spectral region, preventing a suitable detection of low molecular weight
compounds. The possibility to avoid their use will ease both sample preparation
and mass spectrum (MS) interpretation. In recent years nanostructured surfaces
have been proposed as a viable method to achieve such goal but the results are
limited to specific classes of chemical compounds and the approach lacks in
generality. Here we demonstrate that the fluorination of surfaces is the only
step needed to activate the target and to achieve matrix-free operation with
the same detection limit obtained using nanostructured chips. The results of
this work suggest that D/I is a purely interfacial effect, with negligible
contribution from chemical nature of the underlying substrate, provided that
the substrate is conductive and able to efficiently absorb the UV laser beam.
