జర్నల్ ఆఫ్ ఎనలిటికల్ & బయోఅనలిటికల్ టెక్నిక్స్

నైరూప్య

Enhancement of Intact- Ion Yield and Surface Sensitivity by Argon-cluster SIMS

Kozo Mochiji

In secondary ion mass spectrometry (SIMS) of organic samples, damages induced by the primary ions are crucial. The mass of intact ions (secondary ions not dissociated) currently detectable is only as high as the 1,000 Da at best, which prevents the technique from being extended to apply to organic molecules with larger mass. We developed SIMS equipment in which the primary ions were argon cluster ions having a kinetic energy per atom controlled down to 1eV. By applying this equipment to several peptides and proteins, the intensity of fragment ions was decreased by a factor of 102 when the kinetic energy per atom was decreased below 5 eV, and intact ions of cytochrome C (molecular weight: 12,327) and chymotrypsin (molecular weight: 25,000) were detected without using any matrix. Furthermore, we found that argon cluster ions sputter ultra thin layer (~ 2 nm) of organic material and enhance surface sensitivity in SIMS. Based upon the above results, a future prospect of argon-cluster projectile for SIMS is discussed.