Peak fitting to resolve CN- isotope ratios in biological and environmental samples using TOF-SIMS

Our research has focused on developing TOF-SIMS to measure organic N-15 in environmental samples [Appl. Environ. Microbiol. 68 (8) (2002) 4067]. Our goal was to develop a peak-fitting algorithm that would successfully remove the isobaric interferences of Al- and (CN-)-C-13-N-14 from (CN-)-C-12-N-15 ions under conditions of low mass resolution inherent in environmental samples. We tested a variety of peak-fitting models and found that the EMG + GMG (E + G) model performed better than the standard peak shape shifting method under conditions of high mass resolution, unless Al- was present as an interference. Under conditions of Al- interference and low N-15 content, the standard method performed better than the E + G model. As N-15 content increased, the E + G model worked comparably or better than the standard method. Limited mass resolution during analysis of organic N-15 standards on kaolin clay dictated using the standard method which performed acceptably on standards containing greater than 1 at.% N-15. These data emphasize the potential utility of using analytical models to resolve isobaric interferences in TOF-SIMS. (C) 2004 Elsevier B.V. All rights reserved.