Transmission Secondary Ion Mass Spectrometry of a Peptide Using 5 MeV C₆₀⁺ Ions

Abstract

Transmission secondary ion mass spectrometry (transmission SIMS) of thin films of leucine-enkephalin using MeV C₆₀⁺ primary ions was performed to examine the advantage of the combination with detection of secondary ions emitted in the forward direction in efficient emission of the intact molecular ions. Leucine-enkephalin thin films deposited on self-supporting SiN membranes were bombarded with 5 MeV C₆₀ ions, and positive secondary ions emitted in the forward and backward directions were mass-analyzed. The yield of fragment ions emitted in the forward direction was remarkably reduced compared to the backward direction, while the yield of intact molecular ions was reduced to a minor extent depending on the thickness of the peptide film. This suggests a potential of forward emission geometry in transmission cluster ion SIMS for less-damage and sensitive analysis of biological materials.