SIMS Mass Interferences SIMS Theory Mass Interferences Mass interferences occur whenever another ion has the same nominal mass as the analyte ion. Such interferences are called isobaric.
Oxides are common interferences since oxygen-metal bonds are particularly stable.
Low intensity hydrides of many elements appear one mass unit higher than the elements themselves. Primary ions often combine with sample elements to produce interferences. The exact mass minus the nominal masses is called the mass defect. Mass defects arise from differences in the nuclear binding energies that hold the protons and neutrons together in the nucleus. The curve of mass defects gives atomic ions higher masses than molecular interferences at relatively low masses and the opposite at higher masses.