Liquid chromatographic method and system
To form a smooth gradient and a preparatory liquid chromatographic system having a plurality of syringe type pumps, solvents are alternately drawn and inserted into each cylinder. The solvents are alternately drawn into and through a long narrow path formed of tubing to create axial mixing and spreading out of the interface and then are drawn into the cylinders during the refill stroke of the piston at a sufficiently high velocity to create turbulence. The drawing of the solvents into one side of the cylinder a radial distance from the center creates circular eddy currents.
1. A method of performing preparatory liquid chromatography comprising:
drawing at least first and second solvents into a plurality of pumps from at least a corresponding first and second source of solvents;
pumping said at least first and second solvents from said plurality of pumps;
said step of drawing said at least first and second solvents including the step of mixing said at least first and second solvents together without using a separate mixer whereby a gradient for a preparatory liquid chromatographic system is formed;
said step of mixing including the step of mixing said at least first and second solvents in said plurality of pumps during a refill portion of a pump cycle prior to pumping said at least first and second solvents from said plurality of pumps during a delivery portion of the pump cycle;
said step of mixing further including the step of drawing said first and second solvents through at least one flow path, wherein the at least one flow path is shaped to produce good axial mixing and poor transverse mixing by stretching out flow streams of each of said first and second solvents; and
said step of mixing further including the step of drawing said at least first and second solvents into a pump cylinder that is dimensioned with respect to the at least one flow path for good transverse mixing at a rate and pressure that causes turbulence where it undergoes enhanced transverse mixing and axial mixing from eddy currents in the pump cylinder.
2. The method of claim 1 wherein the step of drawing said at least first and second solvents into a pump cylinder includes the step of drawing axially-mixed solvents into the pump cylinder at one side of the pump cylinder wherein circular eddy currents are created in the pump cylinder resulting in enhanced mixing because the axially-mixed solvents entering the pump cylinder are transversely mixed by the circular eddy currents and because the distance required for transverse mixing is small.
3. A method according to claim 2 wherein the enhanced mixing occurs because the tendency of some pairs of liquids not to mix at their interfaces decreases because this interface is already degraded at or before an outlet of the flow path.
4. A method according to claim 1 wherein the step of drawing said at least first and second solvents through at least one flow path comprises the step of drawing said at least first and second solvents through a flow path that has a length of between 10 inches and 250 inches whereby good axial mixing is produced by stretching out flow streams of each of said at least first and second solvents.
5. A method according to claim 1 wherein the step of drawing said at least first and second solvents through at least one flow path comprises the step of drawing said at least first and second solvents through a flow path having a diameter that maintains flow in the transitional stage between laminar and turbulent flow.
6. A method according to claim 1 wherein the step of drawing said at least first and second solvents through at least one flow path comprises the step of drawing said at least first and second solvents through a flow path having a diameter less than one-half the diameter of the pump cylinder.
7. A method according to claim 1 wherein the step of drawing said at least first and second solvents through at least one flow path comprises the step of drawing said at least first and second solvents through a flow path that has a volume less than one-tenth the volume of a charge of solvents into the pump cylinder.
8. A method according to claim 1 in which the step of pumping said at least first and second solvents from said plurality of pumps comprises the steps of drawing solvent into pump cylinders with a refill stroke that is at least three times faster than a delivery stroke wherein turbulence is created in the solvent.
9. A method according to claim 1 in which the step of drawing at least first and second solvents into the pump cylinder comprises the step of drawing at least first and second solvents into pump cylinders that are three to eight inches long and have a ratio of length to diameter of between three and eight.