Varian Associates, Inc.

Other

Miner N Munk

Detlef R Boehme

Kenneth C Judah

Pierre Y Achener

A high pressure liquid chromatography system including a reservoir for a liquid mobile phase, an LC column and detector, a high pressure reciprocating pump for enabling flow from said reservoir through the column, and a positively actuated inlet valve for controlling flow from the reservoir to the pump chamber. The pump is driven by motor means, such as a stepping motor, directly coupled thereto; and the inlet valve is actuated by the power train of the motor and pump, e.g., by an eccentric carried by the pump crank shaft. The pump piston is similarly driven by an eccentric, the pump and inlet valve eccentrics being angularly displaced in their respective positions at the crank shaft, as to delay opening of the inlet valve for a predetermined period following a pump stroke, so as to enable decompression of the liquid in the pump chamber.

High pressure liquid chromatography system

In a liquid chromatography system including a chromatographic column, a reservoir for a slightly compressible liquid mobile phase, piston means cooperating with the reservoir for pumping the liquid phase through the chromatographic column, and means for displacing the piston at a pre-selected velocity, an improvement is disclosed enabling maintenance of a constant flow in the presence of flow resistance changes at the chromatographic column. Such flow resistance changes may arise, for example, in consequence of viscosity changes occurring in the liquid phase during the course of gradient elution operation. According to the improvement, pressure control means are provided in the flow path between the reservoir and column, the pressure control means being adapted for maintaining a substantially constant pressure at the reservoir. In consequence, flow rate changes arising from expansion or contraction of the liquid phase in consequence of compressibility are precluded.

Liquid chromatography pumping system with compensation means for liquid

Single and dual beam flow cells for liquid chromatography that provide good detectability and linear response with small sample volumes. A cylindrical window surrounds the sample flow path to permit focusing convergent light rays through the center of the flow path and along optical paths of equal length through the cell. Optical stops limit the light passing through the cell to convergent rays incident to the window surface. A wide acceptance angle for the rays results in high light transmission and averages variations in light output along the light source. A dual beam flow cell utilizes a common exit for the sample and reference liquids. The flow cells are economically constructed for direct coupling to a chromatographic column by using a standard compression fitting union and can be used in a single wavelength or discrete wavelength detector, or in a spectrophotometer.

Convergent light illuminated flow cell for liquid chromatography

An injection apparatus and method for use in high pressure liquid chromatography. A cylindrical sample holding means containing several sample cells is maintained in a chamber whose pressure is approximately equal to that of the head of the chromatograph separation column. The sample cells are bores through the cylinder, parallel to its axis and spaced along a cylinder of revolution concentric to the axis. The cells are preloaded with samples to be analyzed. Stationary carrier fluid inlet and outlet conduits extend into the chamber above and below corresponding points on the cylinder defined by the sample cell placement. The inlet conduit is connected to a high pressure source of carrier fluid. As the sample holder is rotated, successive sample cells are aligned with the inlet and outlet conduits such that the sample is forced through the outlet conduit into the column. This structure eliminates the need for movable high pressure seals between the outlet conduit and the sample cells, due to the maintenance of all the cells at an elevated pressure.

High pressure sample injector and injection method

A liquid chromatography system including a liquid chromatography column, first and second reservoirs for solvents to be utilized as the mobile phase, reciprocating pumping means for flowing the solvents through the column, and motor means for driving the pump through successive pumping cycles including pump and fill subcycles. First and second solenoid-actuated proportioning valves are positioned at the low pressure side of the pump, i.e. between the first and second reservoirs and the pump inlet. Gradient setting means are provided for setting a preselected solvent proportion to be used over a time period. Means responsive to the gradient setting opens one of the said proportioning valves during a predetermined portion of the fill subcycle. The valves are actuated in complementary fashion with respect to opening and closing; hence the fill subcycle is divided between flow proceeding from the first and second valves in accordance with the gradient setting.

Liquid chromatography system with solvent proportioning

Apparatus and method for detecting the refractive index and rate of fluid flowing through an elongated flow cell, having applications in liquid chromatography. The cell may be of circular cross section and has an input window in one end, an exit window in the other, and a longitudinal side wall. A light source directs divergent light through the entrance window, longitudinally through the cell, to pass through the exit window and be sensed by a photoelectric detector outside the exit window. In a first embodiment, heat transmission apparatus connected to the cell establishes a constant temperature gradient in the cell. This temperature gradient, preferably, has a component perpendicular to the longitudinal dimension of the cell and extending toward the center of the cell. This causes the density of the fluid in the cell to vary as an increasing function of its distance from the walls. The index of refraction of the fluid thus, in this embodiment, increases with distance from the cell walls. This causes the divergent light to be bent away from the cell walls, and toward the center of the cell. The degree of this bending, and hence the fraction of light entering the entrance window which passes through the exit window, increases with the refractive index of the fluid. By appropriate selection of the cell dimensions, of the value of the temperature gradient and of a substantially constant flow rate of the fluid, the bending of the light passing through the cell may be governed such that the fraction of entering light which exits from the cell is a highly dependent function of variations in the refractive index of the fluid in the flow cell. In another embodiment, a fluid having a known refractive index value has its flow rate determined by measuring the absorbance of a beam of light passed therethrough after establishing a temperature gradient in the fluid such that the degree of light bending is influenced by the flow rate.

Refractive index and flow rate detector and method

Solvent gradient generating apparatus in a liquid column chromatography system. A multi-compartment vessel having an input/output port pair for each compartment is coupled between a high pressure pump and the column cell for providing both gradient generation and pulse damping. A piston, which is slidably contained within the vessel, sealably provides the compartments. Means external to the vessel are provided for controlling the rate of movement of the piston within the vessel. The volume of each compartment is controlled by the position of the piston, and the rate of movement of the piston controls mixing of the solvent components delivered to the column cell. Each compartment has input and output ports. In one embodiment, both input ports are coupled to the high pressure pump while only one output port is coupled to the column cell. In another embodiment, only one input port is coupled to the pump and the other input port and one output port are sealed.

Solvent gradient generator for chromatography systems

Apparatus and method applicable to liquid chromatography for continuously detecting the viscosity of the effluent from an analysis column of a chromatograph system. The effluent is forced through a tubular path in a flow resistance element, which may contain a packing material to increase the amount of energy dissipated in the flow resistance element. The temperature of the effluent is sensed before and after passage through the path. A signal is generated which is a function of the difference between the value of temperature which is sensed before and after traversal of the effluent through the tubular path. From these measurements, the viscosity of the effluent may be computed as a function of the observed temperature change.

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Walnut Creek, CA, United States of America

Miner N Munk