What factors affect the use of mobile phases?

 **Author:Orginal from Internet

We are all aware of the importance of mobile phases; should there be a problem with the mobile phase, the results from the analytical instrument lose their reference value. However, there has always been a great deal of uncertainty regarding their validity for many people, with many relying on experience to determine this. So, what can those without experience rely on?

Some might say they rely on documentation, but are there any relevant validation documents regarding the shelf life of mobile phases, or any specified shelf-life guidelines for reference? The answer is no; even online, there are no specific regulatory documents detailing the shelf life for each individual mobile phase. Most shelf-life guidelines are based on the stability and chemical properties of reagents or commonly used chemicals, with the exact duration depending on the prevailing environmental conditions. It could be said, therefore, that determining the shelf life of a mobile phase is largely a matter of experience. Today, we have summarised the guiding principles regarding the shelf life of mobile phases, as well as regulations on storage and re-testing.

Factors affecting the storage life of mobile phases

1. Volatilisation of organic components: The higher the proportion of organic reagents and the lower their boiling point, the greater the degree of volatilisation. However, volatilisation is relatively easy to control; it simply requires the container to be sealed properly;

2. Effect of pH: Reversed-phase chromatography mobile phases often consist of buffer salts; their pH is affected by the volatilisation of the organic phase and carbon dioxide in the air, sometimes even causing turbidity. Furthermore, the extent of this effect varies depending on the pH and the specific buffer salt used;

3. Effect of Microorganisms: Over time, aqueous systems are prone to microbial growth, particularly when exposed to light; consequently, they are often stored in amber bottles; Furthermore, the higher the proportion of the organic phase in the mobile phase, the less likely it is to support microbial growth; consequently, the shelf life varies depending on storage conditions and the proportion of the organic phase.

Chemical Reagents for Preparing Mobile Phases

1. Most laboratory reagents do not specify a shelf life, as chemical reagents generally do not deteriorate provided they are stored correctly.

2. However, this does not apply to the service life of the preparations. During storage, and particularly when dispensing the preparations, unavoidable contact with air or other substances may occur; this can lead to slow reactions, and once these accumulate to a certain extent, the product is deemed to have deteriorated. Consequently, no expiry date is indicated on the label.

3. Some chemical preparations require testing prior to use; if the level of impurities exceeds the standard and affects their usability, they may be deemed to have deteriorated and must not be used.