Recognising multiply charged species

Multiply charged species can be seen when using ESI. In positive ion mode, the number of charged species normally observed is determined by the number of basic sites on a molecule that can be protonated at low pH. Singly charged species will show isotopic peaks that differ by 1 mass unit doubly charged ions show isotopic peaks that differ by 0.5 mass units. 

The molecular mass can be deduced using the equation below  

In general, a mass separation of 0.5-0.7 Da would be indicative of a doubly charged ion. Similarly, a separation of only 0.3 mass units would indicate a triply charged ion. 

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