Solvent mixing in hplc using low pressure solvent metering pumps

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. The cell having first and second spaced-apart electrodes in contact with the solvent mixture accumulated in the cell. One of the electrodes receives an applied electrical excitation. The other electrode senses the applied excitation through the accumulated solvent mixture and produces an excitation response functionally related to the volume of accumulated solvent mixture. An electrical control circuit connected to the detector cell and coupled to the pump speed controller responds to the detector excitation response and produces a control input to the pump controller that selectively inhibits and enables operation of the solvent metering pumps as required to meet the intake of the high pressure pump without wastage or excessive loss of compositional response.