Please explain the principles, advantages, and disadvantages of NCI.
NCI (Negative Chemical Ionization)
Both EI and CI measure positive ions (ions with electrons missing). On the other hand, there is also a method for using negative ions (ions with extra electrons) created in an ion source.Although negative ions also appear with the EI method, the volume created is small and cannot be used effectively. The chemical ionization method utilizing negative ions is the NCI method. The advantage of NCI is compound selectivity. Compounds with high electron affinities are selectively ionized. For these types of compounds, very high sensitivity can be obtained in comparison with the EI and CI methods.