Modifying Solvent Compressibility for LC Pumps in OpenLab CDS

Answer

This Information Applies To: Agilent OpenLab CDS, G7110B Isocratic Pump, G7111A/B, G5654A Quaternary Pumps, and G7112B Binary Pump.

Issue

Incorrectly applied solvent compressibilities can result in an increased pressure ripple, or inaccurate solvent composition in LC pumps.

Background

In HPLC, liquids under high pressures are pumped through the system, which can result in measurable liquid compression. Though the amount of compression is very small, it is enough to change the flow rate of the system. Incorrect compressibility compensation will affect the resulting volume of solvent that is moved to the system, leading to pressure ripples, and inaccurate solvent compositions.

Steps to Follow

1. In the acquisition software, from the Home tab, access the Method screen. There are two options:
   • Click the Method button, or
   • Right-click the pump in the Instrument Status window and from the contextual menu, click Method (See Figure 1). 

     
     
     Figure 1. Accessing method screen
     1. Method from layouts, 2. Method from instrument status
      

2. From the left pane, select the pump, then expand the Advanced tab of the pump to access the compressibility settings. The settings are currently being applied to the selected solvents. (Figure 2).

   
   
   Figure 2. Modifying Solvent Compressibility 
   1. Compressibility settings, 2. Selected solvents
   
   

   You can change the compressibility setting by overwriting the value in the box. The default value will vary depending on the model of pump that is configured. Only values within the range of 40×10^-6 per bar to 150×10^-6 per bar can be entered. When you are using solvents with large compressibility differences on the same pump head, use the default value. 
   
   

   Tips: For binary pumps, you can adjust the value for each individual pump head. Isocratic and quaternary pumps will only have one value that can be adjusted.

3. If the Use Solvent Types check box is selected, you will be unable to modify the compressibility values, and the options will disappear. Instead, you will be able to select the solvent being used for each channel from a drop-down list in the Solvents section. Based on the selection chosen, a compressibility setting will be applied from a database of calibrated values (Figure 3).

   
   
   Figure 3. Accessing the solvent selection drop-down list
   1. Use Solvent Types check box, 2. Solvent Selection drop-down list
   
   

   Learn how to effectively operate your Agilent Infinity LC: HPLC-OLII-1121e - Agilent Infinity LC Systems with OpenLab CDS – Acquisition Method e-learning course available from Agilent education