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 15N 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 13C14N from 12C15N ions under conditions of low mass resolution inherent in environmental samples. We tested a variety of peak-fitting models and found that the EMG þ GMGðE þ GÞ 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 15N content, the standard method performed better than the E þ G model. As 15N content increased, the E þ G model worked comparably or better than the standard method. Limited mass resolution during analysis of organic 15N standards on kaolin clay dictated using the standard method which performed acceptably on standards containing greater than 1 at.% 15N. These data emphasize the potential utility of using analytical models to resolve isobaric interferences in TOF-SIMS. # 2004 Elsevier B.V. All rights reserved.