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Solvent-mixing-in-HPLC-using-low-pressure-solvent-metering-pumps

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Solvent mixing in HPLC using low pressure solvent metering pumps

Details

Inventors: Baldwin, Lawrence G.; Ehrlich, Burney J.; Dixon, Jack B.;
Assignee: Tracor, Inc. (Austin, TX)
Primary Examiner: Adee; John
Assistant Examiner:
Attorney, Agent or Firm: Arnold, White & Durkee

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.

DETAILED DESCRIPTION The present invention provides improvements in liquid chromatography systems in which two or more solvents are mixed in prescribed proportions to form a solvent mixture ultimately to be introduced into a chromatograph column as a carrier for the mobile phase.
In particular, the present invention has utility and provides an improvement in a liquid chromatograph having solvent mixing apparatus which includes two or more solvent metering pumps, each providing a flow of one solvent at a rate dependent upon pump speed, with the individual solvent flows being combined to form a solvent mixture of a composition determined by the relative flow rates of the individual solvent flows and at a total flow rate that is the sum of the individual flow rates.
Control of the speeds of the metering pumps and regulation of the total flow rate of the solvent mixture is provided by a pump speed controller.
Aspects of the present invention may, however, also provide for improvement of a liquid chormatograph having solvent mixing apparatus in the form of a proportioning valve mechanism which accesses individual solvents on a time share basis for withdrawal and delivery to a mixing chamber, such as by a low pressure pump.
The volume of each individual solvent withdrawn during the time it is accessed (and thus the volume of solvent mixture formed within each cycle of operation of the proportioning valve mechanism) is established by the speed of the pump as it withdraws the solvents.
The formation of a certain volume of solvent mixture within each cycle of operation of the proportioning valve mechanism and made available from the mixing chamber constitutes a flow of solvent mixture at a particular flow rate.
Recognizing the need for enhanced compositional accuracy in solvent mixtures introduced to the column of a liquid chromatograph, a feature of the present invention is that of providing for the first time realization of low pressure solvent mixing in a liquid chromatograph without sacrifice of compositional response or substantial solvent wastage

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