Sound is generated in a reference cell and a measuring cell. An eluted component passing through the measuring cell changes the velocity of sound in the cell. This change is detected by a phase shift of acoustic signals between the two cells. This detector is usually employed for inorganic gases in the region where @T06299@ detectors are not sufficiently sensitive. The detection threshold is of the order of \(0.1\ \text{ppmv}\). The linear dynamic range is of the order of \(10^{3}\).