FORMATION AND EMISSION OF TETRAALKYLAMMONIUM SALT MOLECULAR-IONS SPUTTERED FROM A GELATIN MATRIX

A gelatin matrix was simultaneously doped with nine equimolar, homolog ous, tetraalkylammonium salts ranging in mass from 210 to 770 Da. Bomb ardment of the sample with kiloelectronvolt ions resulted in a noniden tical distribution of relative cation intensities with a maximum at m/ z 242 for samples with a total salt concentration of 0.004 g of salt/g of gelatin. A rapid increase in relative intensities with increasing mass is observed for the low mass salts and is believed to be linked t o changes in the ionization efficiencies. The changes. in ionization e fficiencies are likely related to decreasing coulombic attractive forc es between the organic cation and the counterion. Disappearance cross sections, determined from decay curves, indicate that sputter-induced damage increases with increasing mass of the cation. Fragment-to-intac t cation ratios also suggest that damage accumulates fastest in the he aviest salts. These observations indicate that desorption yields of th e organic salts in a gelatin matrix decrease with increasing mass. In addition, suppression of lower mass tetraalkylammonium salt intact cat ion intensities was observed for salt-in-gelatin concentrations greate r than 10(-3) g/g.