Ambient mass spectrometry has been increasingly applied for sensitive detection of trace organic compounds present in complex matrixes. In the real world, detection of trace amounts of inorganic species, particularly with speciation information, is of great significances. Herein a method based on extractive electrospray ionization (EESI) tandem mass spectrometry (MS/MS) has been established for rapid detection of radioactive inorganic species in natural water samples. Negatively charged uranyl acetate undergoes characteristic fragmentation in the gas phase, providing the fundamental chemistry for specific detection of uranyl species in complex matrixes without sample pretreatment. Under the optimized experimental conditions, uranyl species in various natural water samples were rapidly detected using multiple-stage EESI mass spectrometry. The mean time for each sample analysis was about 10 s. The limit of detection was about a few 10(-3) ng/L of uranium by utilizing the characteristic fragments obtained in the EESI-MS(3) experiments. The typical relative standard deviation (RSD) of this method was 6.9-8.1% for 8 measurements (S/N = 3). The dynamic response range was 10(-1)-10(3) ng/L for uranium in water samples. The isotope ratio of uranyl species was quantitatively detected using EESI-MS experiments. The results show that EESI-MS, a typical method initially developed for organic compound analysis, has promising perspectives for real time, online monitoring of inorganic species such as uranyl species in natural water samples.