Novel nitrogen rich carbon dots were synthesized via a hydrothermal method by using with 2,4,6-triamino-pyrimidine as the precursor. X-ray photoelectron spectroscopy showed that the carbon dots contained 41 at.% nitrogen; this is significantly higher than previously reported values for similar materials. When exposed to ultraviolet light, the carbon dots in solution emitted bright blue fluorescence, with a maximum quantum yield of 74.9%. The fluorescence was selectively quenched by Hg(II) at pH 6 and Ag(I) at pH 11, with detection limits of 11.4 and 10.3 nM, respectively. Analysis of the fluorescence lifetimes of the carbon dots showed that the fluorescence-quenching mechanism for Hg(II) differed from that for Ag(I). In analysis of lake water, the nitrogen rich carbon dots were highly sensitive, and gave a wide linear range and satisfactory recovery. These results suggest that the carbon dots are suitable for use as novel metal ion probes for the selective detection of different ions at different pH values.