Field desorption mass spectral fragmentation of monosaccharide isomers

Field desorption ionization of selected monosaccharide isomers by potassium ion attachment in high fields is described. The ionization is obtained with a tungsten wire activated with carbon needles and covered with KH2PO4 salt. In addition to the potassium cationized molecular ions, reproducible fragmentation was obtained at 10 mA and 20 mA typical of the various monosaccharides. For instance, D‐glucose tends to lose a water molecule, whereas D‐fructose loses primarily methanol under similar conditions. Methanol elimination is suggested to be characteristic of furanoidal ketoses and water elimination for pyranoidal aldoses, whereas glycol elimination occurs for furanoidal aldoses.