Matrix effects in negative-ion field desorption mass spectrometry

The negative ion mode of field desorption mass spectrometry is matrix dependent. The matrix is used to facilitate the desolvation of ions at field strengths below the onset of field induced electron detachment. The role of the matrix in the desolvation mechanism for negative ions is briefly described and the main properties of a matrix solution, such as viscosity, solubility for complex salts and acids, and adhesion to the emitter surface, on the ion formation are discussed. The application of matrix mixtures with strong adhesion to the emitter surface even at elevated temperatures and high field strengths are considered to be important for the further improvement of this ionization method.