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 ¹⁵ N 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 ¹³ C ¹⁴ N ^- from ¹² C ¹⁵ N ^- 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 ¹⁵ N content, the standard method performed better than the E+G model. As ¹⁵ N content increased, the E+G model worked comparably or better than the standard method. Limited mass resolution during analysis of organic ¹⁵ N standards on kaolin clay dictated using the standard method which performed acceptably on standards containing greater than 1at.% ¹⁵ N. These data emphasize the potential utility of using analytical models to resolve isobaric interferences in TOF-SIMS.