Negative field desorption mass spectra of 30 organic acids (mostly simple sulfonic acids) or their salts has been reported in this paper. Most of the acids studied give rise to the formation of simple negative ions in. [M - M]- or [M - salt option](-) Very low fragmentation or the parent molecules is observed. Addition of additive such as LiCl enhances the intensity of ion signals. Cluster of these molecules are also observed but their intensity is very Low.

Negative ion field desorption mass spectrometry (NFD MS) has been applied to some nucleotides. Polyethylene glycol (PEG 4000) was used as a matrix to facilitate the ion formation at low field strengths and temperatures. Molecular ions of mononucleotides could be obtained with no or a low level of fragmentation. In contrast, NFD mass spectra of dinucleotides and a mononucleotide triphosphate did not exhibit molecular ions but only fragment ions.

AbstractThe 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.