Solvent mixing in HPLC using low pressure solvent metering pumps

In a liquid chromatograph including at least first and second solvent sources, a controller for establishing the composition and total flow rate of a solvent mixture produced, and a column, the improvement comprising:

• a first low pressure metering pump for providing a flow of the first solvent;
• a second low pressure metering pump for providing a flow of the second solvent;
• each pump providing the flow of the respective solvent at a rate dependent upon pump speed as established by the controller;
• means receiving the first and second solvent flows for mixing the same at low pressure to produce a solvent mixture flowing at a rate approximately equal to the sum of the individual solvent flow rates;
• a high pressure pump taking in solvent mixture at an intake flow rate for driving the column to establish therein a flow of solvent mixture;
• a solvent mixture flow path defined between the individual solvent mixing means and the high pressure pump;
• a detector cell disposed in the solvent mixture flow path;
• the cell having 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 pump, 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 flows;
• the cell having first and second spaced-apart electrodes in contact with the solvent mixture accumulated in the cell, one of the electrodes being provided to receive an applied electrical excitation and the other electrode being provided to sense the applied excitation through the accumulated solvent mixture and produce an excitation response functionally related to the volume of the accumulated solvent mixture;
• and
• an electrical control circuit connected to the detector cell and coupled to the pump speed controller, the circuit responding to the detector excitation response, to produce a control input to the pump controller for selectively inhibiting and enabling operation of the solvent metering pumps.

In a liquid chromatograph having solvent mixing apparatus including two or more solvent metering pumps, each providing a flow of solvent at a rate dependent upon the respective pump speed for combination into a combined solvent flow to form a proportioned solvent mixture at a total flow rate that is the combination of the individual solvent flow rates, and a controller for regulating the total flow rate of the formed solvent mixture by synchronously varying in identical proportion the speeds of the solvent metering pumps, the improvement comprising:

• a detector cell having an inlet supply port for receiving the formed solvent mixture at a first flow rate approximating the total flow rate and having an outlet port to provide for withdrawal of the formed solvent mixture from the cell at a second flow rate, the cell holding a volume of solvent mixture accumulated in an amount dependent upon the relative rates at which solvent mixture is received and withdrawn;
• the detector cell includes first and second spaced-apart electrodes in contact with the solvent mixture accumulated in the cell, one of the electrodes receiving an applied electrical excitation and the other electrode sensing the applied excitation through the accumulated solvent mixture between the electrodes to produce an excitation response signal functionally related to the volume of the accumulated solvent mixture;
• the detector cell being sensitive to the electrical properties of the solvent mixture accumulated in the cell to produce the excitation response signal;
• a reference signal source providing a signal representative of a reference volume amount of cell accumulated solvent mixture;
• a comparator receiving the detector cell output signal and the reference signal for producing an output signal indicative of the volume amount of accumulated solvent mixture in the detector cell relative to the reference volume amount;
• and
• means electrically connected to the comparator and coupled to the pump speed controller for producing a control input to the pump speed controller;
• said means producing a control input to the pump speed controller that inhibits operation of the solvent metering pumps in response to a comparator output signal indication that the volume amount of accumulated solvent mixture in the cell is greater than the reference volume amount, and producing a control input to the pump speed controller that enables normal operation of the solvent metering pumps in response to a comparator output signal indication that the volume amount of accumulated solvent mixture in the cell is less than the reference volume amount.

In a liquid chromatograph having solvent mixing apparatus producing a solvent mixture flow and including two or more solvent metering pumps, each driven by a stepping motor in response to pulses produced by a pulse generator, the improvement comprising:

• a cell for receiving the solvent mixture flow produced by the solvent mixing apparatus and providing for withdrawal therefrom of a solvent mixture flow, the cell holding a volume of solvent mixture accumulated in an amount dependent upon the rates at which solvent mixtures are received and withdrawn;
• the cell comprising a chamber having an inlet supply port receiving an input flow of solvent mixture at a first flow rate from the solvent mixing apparatus and an outlet port for withdrawal of an output flow rate at a second flow rate;
• a detector sensitive to the volume amount of solvent mixture accumulated in the cell and producing an output signal representative thereof;
• the detector comprising an electrical admittance measurement device including first and second spaced-apart electrodes in contact with the solvent mixture accumulating in the cell, one of the electrodes receiving an applied electrical excitation and the other electrode sensing the applied excitation through the accumulated solvent mixture between the electrodes to produce an excitation response output signal functionally related to the volume of the accumulated solvent mixture;
• a comparator receiving the detector output signal and a signal representative of a reference volume amount of cell accumulated solvent mixture for comparison;
• the comparator producing an output signal of a first signal level when the comparison indicates that the volume amount of solvent mixture in the cell exceeds the reference volume amount and producing an output signal of a second signal level when the comparison indicates that the volume amount of solvent mixture in the cell is less than the reference volume amount;
• an electrical output circuit electrically connected to the comparator and coupled to the pulse generator;
• and
• the circuit being operable in response to the first signal level of the comparator output signal to inhibit pulse production by the pulse generator and thereby synchronously stop the solvent metering pumps, and the circuit being operable in response to the second signal level of the comparator output signal to enable pulse production by the pulse generator.