How can mobile phase vials meet the requirements of routine analytical operations?

**Author: Original from Internet

The solvent bottle is the starting point for the mobile phase and is typically used to hold either an aqueous solution or an organic solution.

For aqueous solutions, the primary concern is preventing contamination. Although the water used in liquid chromatography is generally sterilised, bacteria are highly resilient; under suitable temperature and light conditions, they become active, and the addition of additives such as phosphates to the mobile phase further accelerates their growth. Therefore, a crucial task regarding solvent vials is to replace the mobile phase frequently to ensure it remains fresh.

With organic-phase solutions, there is no need to worry about bacterial growth. However, organic phases are prone to polymerisation; acetonitrile, in particular, polymerises very easily under suitable light conditions, resulting in flocculent polymerised precipitates forming in the bottle. To prevent polymerisation, use brown solvent bottles when storing acetonitrile to avoid direct sunlight, and discard any residual solution at the bottom of the bottle when replacing it.

The filter head in the solvent bottle serves to prevent particulate impurities from entering the instrument’s flow system. It is typically made of sintered quartz glass or stainless steel. If it becomes blocked, it will cause poor flow of the mobile phase; therefore, it must be cleaned. Glass filter heads are usually soaked in dilute nitric acid, whilst stainless steel ones can be ultrasonically cleaned directly.

The purpose of degassing is to remove dissolved gases from the mobile phase, ensuring accurate fluid delivery by the chromatographic pump and improving the reproducibility of retention times and peak areas; stabilising the baseline and increasing the signal-to-noise ratio; preventing bubble-induced peak broadening, thereby enhancing detector performance; and reducing dead volume and preventing packing oxidation, thus protecting the chromatographic column.

Currently, the following four degassing methods are commonly used:

(1) Helium degassing: This method utilizes the fact that helium has a lower solubility in liquids than air; continuous helium purging yields good results but is costly;

(2) Heating and reflux: This method is effective but involves complex operations and poses a risk of contamination from toxic vapors;

(3) Vacuum degassing: This method tends to remove the organic phase;

(4) Ultrasonic degassing: The mobile phase is placed in an ultrasonic vessel and agitated with ultrasonic waves for 10–15 minutes; whilst this method is less effective, it is simple to operate. In practice, the ultrasonic degassing method remains widely used due to its simplicity. Although this method may occasionally lead to an increase in gas solubility, it generally meets the requirements of routine analytical operations.