Abstract: A response characteristics of a microwave spectroscopic measuring system is remarkably improved by supplying a carrier to a continuously flowing sample containing a polar substance to be measured quantitatively. The carrier contains a compound having at least similar chemical form to that of the polar substance.

Abstract: In a method of measuring substances each exhibiting a derivative peak of the phase sensitive detector (PSD) output at a pair of specific magnetic field intensities by sweeping the field, the magnetic field is switched between the specific magnetic field intensities to obtain only the absorptions at the specific field intensities to thereby substantially reduce the sweeping time as well as to reduce the background drift.

Abstract: A gas sample including polar molecules is introduced into a cavity (an internal space) of a cavity resonator, the cavity being provided therein with a Stark electrode which is vertically of a microwave electric field resonating at the microwave frequency, and a direct current Stark voltage which is applied to the Stark electrode together with a sine wave modulation voltage is swept, resulting in a microwave absorption spectrum representing the polar molecules in the gas sample. The resonance frequency of the cavity may be made variable to observe various polar molecules individually.