Abstract: A liquid chromatograph for HPLC utilizes low pressure solvent metering pumps for solvent mixing in series with a high pressure pump driving the column. Solvent mixture is provided at a flow based upon the intake demand of the high pressure pump. Such operation is obtained by the use of flow control apparatus disposed between the solvent metering pumps and the high pressure pump. The flow control apparatus includes a detector cell disposed in the solvent mixture flow path between the metering pumps and the high pressure pump. The cell has an inlet port for receiving an input flow of solvent mixture into the cell from the solvent mixing means, an outlet port for withdrawal of an output flow of solvent mixture by the high pressure pumps, and a reservoir between the inlet and outlet ports for holding a volume of solvent mixture accumulated in an amount dependent upon the relative flow rates of the cell input and output flow.

Abstract: A method and apparatus for preventing the destruction of an alkali source in a nitrogen-phosphorus detector by certain reactive and derivatizing reagents encountered in gas chromatography is disclosed. Protection is afforded by lowering the temperature of an electrically heated alkali source during the period in which offensive substances in a gas under analysis are eluted, with the temperature of the source being restored after passage of the offensive substances. The temperature of the alkali source is changed by altering the current through an electrical resistance heater with a temperature control circuit that utilizes a wheatstone bridge.