To provide a method for facilitating ionization without reacting with a sample, using an electronic atomization ionization mass spectrograph.

This electronic atomization ionization mass spectrometry includes a step for analyzing the non-chargeable, non-basic and low-polar sample in a polar solvent, using a salt as an additive. A precursor of a mixture state is composition-analyzed thereby, initial thin film quality and stability of the precursor, for example, are predicted thereby before applying a process for a silicon compound of a low dielectric thin film material, measuring sensitivity is improved to reduce a sample amount required in analysis to several μg, and the efficiently improved mass spectrometry is provided since a molecular weight is measurable even when no intramolecular specified functional group exists.