Handling, Preparation and Storage of Standards

Storage

The following are some considerations you may want to make before the storage of chemical standard solutions:

1. Know the chemical stability of your standard. Chemical stability can be altered by changes in starting materials and preparation conditions. It is therefore advisable to perform stability studies on all standard solutions to avoid time consuming and costly delays or mistakes and to strictly adhere to preparation methodology, including order of addition for multi-component standard solutions.
2. Note the temperature during storage and attempt to maintain a storage temperature at or around 20 °C. Some standards are not stable for long periods at room temperature and require refrigeration or even freezing.
3. Perform the stability study in the container material selected for storage. It is not advisable to use volumetric flasks as storage containers due to expense, contamination, and transpiration issues.
4. Determine if the standard is photosensitive and/or store in the dark if there is a concern. This is an issue with some of the precious metals and is a function of matrix. Photosensitivity will increase in the presence of higher energy light (sunlight as opposed to artificial light) and trace or minor amounts of organics especially if there is an extractable proton alpha to an electron withdrawing functional group such as a carbonyl group. The presence of chloride may increase instability to photo reduction. A classic example is Ag⁺ in HCl solutions.
5. Store the standard in containers that will not contribute to contamination of the standard. LDPE is an excellent container for most inorganic standards.
6. Weigh the standard solution before storage and then just before the next use. If there is measurable transpiration the weight will decrease with time.

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