**3. Conclusions and Future Directions**

### **3.1 Conclusions**

In summary, a novel strategy for direct MS analysis of metal speciation in geological samples was proposed by regulating the interaction process between reagents/energy and geological samples, and a sequential ionization device was home-built which can be directly coupled to the commercial mass spectrometer (e.g., ICP-MS, ESI-MS) for the direct MS analysis of geological samples. Rapid sequential characterization of metal speciation in multiple geological samples, such as minerals, fossils, soil, and bio-tissue has been quantitatively achieved based on the sequential analytical strategy and ionization device, without complex sample pretreatment. Compared with traditional methods (e.g., BCR method, Tessier method), the present method offers significant advantages such as high analysis speed, low sample consumption, high recovery, simple operation, low energy and labor consumption, and rich chemical information. These results demonstrate the power of the present method for obtaining information on element abundance, occurrence, and paragenetic association, which is vitally essential for geochemistry.
