PURPOSE: To enable quantitative analysis on at least two components of neutral, acid and basic organic compounds handily at a high accuracy by adsorbing a sample of a liquid or a gas using at least two of neutral, acid, and basic adsorbents.

CONSTITUTION: Samples 1 as neutral, acid and basic organic compounds are placed into a quartz tube together with a neutral adsorbent 2, an acid adsorbent 3 and a basic adsorbent 4 and introduced direct into a mass spectrometer 5 separately to determine a mass spectrum corresponding to substances yet to be adsorbed by the adsorbents 2, 3 and 4 by mass spectrometry. Spectrums obtained by the mass spectrograph 5 are computed and a quantitative analysis on neutral, acid and basic organic compounds is possible by computation. When it is found previously that the samples 1 do not contain one component of the neutral, acid and basic organic compounds, two of the neutral, acid and basic adsorbents may be used.