Topics - Katherometer
Katherometer is the name given to the sensor of a thermal conductivity detector. It consists of a thermostatted metal block containing two cylindrical cells. The gaseous eluent from the column passes through one cell and though the other passes a reference flow of the same gas, at the same flow rate. In each cell is situated a wire filament which may be axial to the cell or, in a cavity, at the side of the cell. The two filaments are situated in the arms of a Wheatstone bridge and a current passes through each. At thermal equilibrium the heat lost from each filament is balanced by the heat generated by the electric current and the filaments come to an equilibrium temperature. When solute vapor from the column enters the sensor cell, the thermal conditions around the filament change, causing a change in temperature and a corresponding change in filament resistance. The bridge becomes out-of-balance and the out-of-balance signal is fed to an amplifier and thence to a recorder of computer. The katherometer has a sensitivity of about 1-6 to 10-7 g per ml.