Methods for Injecting Samples in Liquid Chromatography, Particularly in High Performance Liquid Chromatography

Abstract

A sample injection method for liquid chromatography is performed with an injection valve having a waste port, two sample loop ports, and two high-pressure ports. One high-pressure port can be connected to a pump and the other high-pressure port can be connected to a chromatography column. A sample loop is connected to one of the sample loop ports on one end and to a pump volume of a sample conveying device on the other end. A section of the sample loop can be separated to facilitate receiving a sample fluid in the sample loop. A control unit controls the injection valve and the sample conveying device. The sample injector allows a sample to be loaded into the sample loop and then pressurized to an operating pressure prior to injecting the sample into the chromatography column. The sample loop may also be isolated from the operating pressure for facilitating depressurization of the loop.

1 . A method of operating a liquid chromatography system, the method including:
 (a) isolating a sample loop of the liquid chromatography system from a high-pressure loop of the liquid chromatography system;   (b) performing a pressure compensation operation including one of (i) when isolating the sample loop from the high-pressure loop leaves the sample loop at essentially an operating pressure of a liquid chromatography column, increasing a volume connected in the sample loop to reduce the pressure in the sample loop to essentially ambient pressure, or (ii) when the isolated sample loop is at essentially ambient pressure preparatory to injecting a sample liquid into the high-pressure loop, decreasing the volume connected in the sample loop to increase the pressure in the sample loop to essentially the operating pressure of the liquid chromatography column; and   (c) when the pressure compensation operation comprises decreasing the volume connected in the sample loop to increase the pressure in the sample loop to essentially the operating pressure of the liquid chromatography column, further including connecting the sample loop to the high-pressure loop so that a pump pressure from a high-pressure pump of the liquid chromatography system is applied to the sample loop and a sample liquid in the sample loop is free to flow from the sample loop through a portion of the high-pressure loop to the chromatography column.   
     
     
         2 . The method of  claim 1  further including, after performing step (c) of  claim 1  to introduce the sample liquid into the chromatography column:
 (a) isolating the sample loop from the high-pressure loop once the sample liquid is introduced into the chromatography column; and 
 (b) increasing the volume connected in the sample loop to reduce the pressure in the sample loop to essentially ambient pressure. 
 
     
     
         3 . The method of  claim 1  wherein isolating the sample loop from the high-pressure loop includes placing an injection valve in a PRESSURE COMPENSATION position in which (i) first and second sample loop ports of the injection valve are closed so as to facilitate pressurization of the sample loop, and (ii) first and second high-pressure ports of the injection valve are connected so as to operatively connect the high-pressure pump to the chromatography column. 
     
     
         4 . The method of  claim 1  wherein placing the injection valve in the PRESSURE COMPENSATION position includes rotating a rotor of the injection valve with respect to a stator of the injection valve. 
     
     
         5 . The method of  claim 1  wherein the volume connected to the sample loop is defined by a cavity in which a movable element is slidably mounted, and wherein changing the volume connected to the sample loop includes sliding the movable element within the cavity. 
     
     
         6 . The method of  claim 5  further including measuring the pressure of a fluid in at least one of the sample loop or the volume connected to the sample loop with a pressure sensor. 
     
     
         7 . The method of  claim 5 , wherein the movable element is connected to a drive device which is operable to move the movable element within the cavity, and further including measuring a force exerted upon the movable element by the drive device. 
     
     
         8 . A method of injecting a sample in a liquid chromatography system, the method including:
 (a) isolating a sample loop of the liquid chromatography system from a high-pressure loop of the liquid chromatography system;   (b) placing a sample liquid in the sample loop preparatory to injecting the sample liquid into the high-pressure loop;   (c) with the sample liquid placed in the sample loop and with the sample loop remaining isolated from the high-pressure loop, performing a pressure compensation operation in which a volume connected in the sample loop is decreased to raise the pressure in the sample loop from ambient pressure to the operating pressure of a liquid chromatography column of the liquid chromatography system; and   (d) connecting the sample loop to the high-pressure loop so that a pump pressure from a high-pressure pump is applied to the sample loop to cause the sample liquid in the sample loop to flow from the sample loop through a portion of the high-pressure loop to the chromatography column.   
     
     
         9 . The method of  claim 8  further including:
 (a) isolating the sample loop from the high-pressure loop of the liquid chromatography system after the sample liquid has flowed into the high-pressure loop; and 
 (b) increasing the volume connected in the sample loop to reduce the pressure in the sample loop to ambient pressure. 
 
     
     
         10 . The method of  claim 8  wherein isolating the sample loop from the high-pressure loop includes placing an injection valve in a PRESSURE COMPENSATION position in which (i) first and second sample loop ports of the injection valve are closed so as to facilitate pressurization of the sample loop, and (ii) first and second high-pressure ports of the injection valve are connected so as to operatively connect the high-pressure pump to the chromatography column. 
     
     
         11 . The method of  claim 10  wherein placing the injection valve in the PRESSURE COMPENSATION position includes rotating a rotor of the injection valve with respect to a stator of the injection valve. 
     
     
         12 . The method of  claim 8  wherein the volume connected to the sample loop is defined by a cavity in which a movable element is slidably mounted, and wherein decreasing the volume connected to the sample loop includes sliding the movable element within the cavity. 
     
     
         13 . The method of  claim 12  further including measuring the pressure of a fluid in at least one of the sample loop or the volume connected to the sample loop with a pressure sensor. 
     
     
         14 . The method of  claim 12  wherein the movable element is connected to a drive device which is operable to move the movable element within the cavity, and further including measuring a force exerted upon the movable element by the drive device. 
     
     
         15 . A method of preparing a liquid chromatography system for receiving a sample liquid, the method including:
 (a) isolating a sample loop of the liquid chromatography system from a high-pressure loop of the liquid chromatography system; and   (b) with the sample loop isolated from the high-pressure loop and with the pressure in the sample loop remaining at an operating pressure of the liquid chromatography column, performing a pressure compensation operation in which a volume connected in the sample loop is increased to reduce the pressure in the sample loop to ambient pressure.   
     
     
         16 . The method of  claim 15  wherein isolating the sample loop from the high-pressure loop includes placing an injection valve in a PRESSURE COMPENSATION position in which (i) first and second sample loop ports of the injection valve are closed so as to facilitate pressurization of the sample loop, and (ii) first and second high-pressure ports of the injection valve are connected so as to operatively connect the high-pressure pump of the liquid chromatography system to the chromatography column. 
     
     
         17 . The method of  claim 16  wherein placing the injection valve in the PRESSURE COMPENSATION position includes rotating a rotor of the injection valve with respect to a stator of the injection valve. 
     
     
         18 . The method of  claim 15  wherein the volume connected to the sample loop is defined by a cavity in which a movable element is slidably mounted, and wherein increasing the volume connected to the sample loop includes sliding the movable element within the cavity. 
     
     
         19 . The method of  claim 18  further including measuring the pressure of a fluid in at least one of the sample loop or the volume connected to the sample loop with a pressure sensor. 
     
     
         20 . The method of  claim 18  wherein the movable element is connected to a drive device which is operable to move the movable element within the cavity, and further including measuring a force exerted upon the movable element by the drive device.