Degassing Mobile Phase Solvents

Tips for Daily Analysis

Degassing Mobile Phase Solvents

Commercial HPLC systems have been available for over 40 years now. During that time, a variety of technological advances have appeared, such as high-precision low-flow peristaltic pumps, injectors with superior reproducibility, and various types of detectors that enable highly sensitive detection. However, as a consequence, chemical factors are now becoming more important in determining whether high-sensitivity analysis or automated continuous analysis can be performed with high reliability or not. For example, this includes factors such as the adsorption and stability of sample components, the selection of mobile phases (or eluents), or addressing reproducibility problems with their preparation. It is also now necessary to be concerned with how dissolved air levels in mobile phases affect detector baseline stability or detection sensitivity.
Adjusting the level of dissolved air in mobile phases can be treated as a mobile phase degassing issue. Therefore, this special feature article has focused on degassing mobile phases by addressing issues ranging from theoretical principles to actual practice. I hope this article will be helpful in selecting and using a degassing method appropriate for your application.
(Initially published in 1991 as LCtalk Special Issue 5)

1 Various Problems That Can Occur Due to Air in Mobile Phases

2 Mechanism of How Air Bubbles Are Generated
2-1) Increase in Solution Temperature
2-2) Decrease in Pressure
2-3) Solvent Mixtures

3 Problems with Formation of Bubbles in Flow Lines
3-1) Solvent Delivery Problems Due to Bubbles Generated Inside the Mobile Phase Bottle
3-2) Solvent Delivery Malfunctions Due to Bubbles Generated Inside the Pump
3-3) Channeling Caused by Bubbles Forming or Accumulating Inside Columns
3-4) Baseline Noise Caused by Bubbles Forming or Accumulating Inside Detector Cells

4 Detrimental Effects of Dissolved Air (Oxygen) on Detection
4-1) Detrimental Effects on Detection Caused by High Levels of Dissolved Oxygen
4-2) Detrimental Effects of High or Changing Levels of Dissolved Oxygen on UV Detection
4-3) Fluctuation in Refractometer Baseline Due to Changes in Dissolved Air Content

5 Degassing Methods
5-1) Heated Stirring (1)
5-2) Vacuum Degassing Using an Aspirator
5-3) Heated Stirring (2)
5-4) Vacuum Degassing Using a Gas-Liquid Separation Membrane
5-5) Degassing by Helium Purging
5-6) Non-Degassing Methods

6 Measures for Specific Analytical Conditions
6-1) How to Achieve a High Sensitivity Baseline for Reversed-Phase Columns and UV Short Wavelengths
6-2) How to Achieve a High Sensitivity Baseline for Sugar Analysis Columns and Refractometers

For Research Use Only. Not for use in diagnostic procedures.

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