We are considering quantitative shotgun proteomics experiments on cultured marine algae using ESI-LC MS/MS followed by analysis by Mascot. It is not overly difficult to culture cells in a 99% 13C medium, so we can expect high rates of 13C protein enrichment. The included metabolic quantification configuration files for Mascot Distiller, however, they use only 15N labeling or 15N combined with 13C. Has a 13C-only configuration file been developed?