Masakazu Kusakari

Development of ambient SIMS using mega-electron-volt-energy ion probe

A new secondary ion mass spectrometry device using an ion probe in the heavy mega-electron-volt (MeV) energy range was developed for detecting large intact molecules with high sensitivity under ambient conditions. The instrument is based on the characteristics induced by the MeV-energy heavy ions, namely, electronic excitation induced in the near-surface region and the high transmission capability under ambient conditions. The secondary ions were transported to the mass analyzer effectively by an electric field and atmospheric gas flow, whereas the chemical impurities from the gas were cleared by using an electric field. In addition, this new ambient analysis approach enables evaluation not only of solid samples, but also of liquid samples that were evaporated under advanced vacuum. In this study, liquid water and samples of a benzoic acid solution were measured under ambient conditions.

Secondary ion emission from leucine and isoleucine under argon gas-cluster ion bombardment

The emission of sputtered ions from isoleucine and leucine specimens under bombardment by 10 keV argon gas-cluster ions Ar1000+ was investigated by orthogonal time-of-flight secondary ion mass spectrometry, in an attempt to examine the possibility of discriminating these amino acids by means of specific differences in their mass spectra. Apart from of the protonated molecular ions (M+H)+ a prolific flux of singly charged and doubly charged molecular cluster ions, (Mn+H)+ (1 ≤ n ≤ 15) and (Mn+2H)2+ (8 ≤ n ≤ 29) was observed. The distributions of the cluster yields Yn as a function of their size n were found to be very similar for both amino acids. In addition, the fraction of emitted fragment and other ion species is typically low, and no distinct differences were detected for isoleucine and leucine. Therefore, the present data seem to indicate that a discrimination of isoleucine and leucine via mass spectrometric means is not possible.