In situ cationization of molecular ions sputtered from organic specimens under cluster bombardment

In an attempt to investigate the possibility of an in situ cationization of molecular ions in time-of-flight secondary ion mass spectrometry, low-energy 500 eV Cs+ ions were implanted in organic materials before their analysis by Bi-3(+) thorn cluster bombardment. Specifically, three different organic samples were used: arginine, leu-enkephalin, and polyethylene glycol (both in a pure state and as a mixture with Na trifluoroacetic acid). For the pristine specimens, characteristic secondary ion species were typically observed: (M+H)(+) in the case of arginine and leu-enkephalin, whereas for polyethylene glycol Na-cationized oligomer ions were detected with masses up to similar to 3000 u. Cs+ was implanted into these samples with fluences ranging from 2 x 10(12) to 8 x 10(13) cm(-2). Already for the lowest implantation fluence, a substantial signal of Cs+ secondary ions was observed in the sputtered flux; it seems to saturate at about 1 x 10(13) Cs+ cm(-2). On the other hand, with increasing Cs incorporation, molecular secondary ions containing Cs were found for arginine and leu-enkephalin, notably (M+Cs)(+), albeit with low intensities. Concurrently, a decrease of the intensities of (M+H)(+) ions was noted. By contrast, for polyethylene glycol, no Cs-adduct ions were observed, neither for the pure nor for the mixed specimens. Furthermore, the implantation of Cs has little influence on the ion emission from these samples. The results seem to indicate that for the applied bombardment conditions Cs+ cationization has a rather limited efficiency. Published by the AVS.