Influence of the storage environment of chemical reagents on the validity period
- The influence of air:
Oxygen in the air easily oxidizes and destroys the reducing agent. Strong alkaline reagents are easy to absorb carbon dioxide and turn into carbonates. Moisture can make some reagents deliquescent and agglomerate; fibers and dust can reduce and discolor some reagents.
- The influence of temperature:
The rate at which the reagent deteriorates is temperature dependent. High temperature in summer will accelerate the decomposition of unstable reagents; severe cold in winter will promote the polymerization of formaldehyde and precipitate deterioration.
- The effect of light:
Ultraviolet rays in sunlight can accelerate the chemical reaction of certain reagents and make them deteriorate (such as silver salts, mercury salts, potassium, sodium, ammonium salts of bromine and iodine and some phenolic reagents).
- The influence of impurities:
The purity of the unstable reagent and its influence on its deterioration cannot be ignored. For example, pure mercury bromide is actually not affected by light, while mercury bromide containing trace amounts of mercurous bromide or organic impurities tends to turn black when exposed to light.
- The effect of storage period:
Unstable reagents may undergo changes such as disproportionation polymerization, decomposition or precipitation after long-term storage. During the storage period and validity period, if the liquid is found to have abnormal phenomena such as stratification, turbidity, discoloration, mildew, etc., when the mobile phase is used for sample detection, the retention time or relative retention time of the sample will change significantly. If the solid is found to absorb moisture, discoloration, etc. Abnormal phenomenon should stop using.
Influence of chemical reagent usage requirements on expiration date
Judging the validity period of chemical reagents according to the requirements of use, the most important point is to judge whether the reagent has an influence on the results, and the validity period needs to be shortened or even scrapped.
Deterioration and protection of chemical reagents
Whether a chemical reagent will deteriorate during storage depends on two factors, both internal and external. The internal factor is the physical and chemical properties determined by the chemical structure of the reagent itself; the external factor is the environmental conditions where the reagent is located. To achieve reasonable storage, firstly, we must understand the relationship between the structure and properties of the reagent, and secondly, we must create an external environment suitable for the storage of reagents.
- Reasons that cause and promote the deterioration of chemical reagents
The environment mainly refers to the storage temperature, light and medium. The medium generally refers to air and mixed impurities. In addition to the oxygen, carbon dioxide and water vapor contained in the air, the storage room often contains vapors from various volatile reagents stored in the air that diffuse into the air, such as hydrogen chloride, nitric acid, hydrogen sulfide, sulfur dioxide, bromine, iodine, and ethylene. , formaldehyde and other vapors; in addition, there is dust floating in the air, including inorganic and organic substances and various microorganisms.
Chemical reagents will gradually change and deteriorate under certain temperature, light and medium conditions. This process has physical changes and chemical changes. The former causes the loss of chemical reagents, while the latter can make the reagents completely deteriorate and fail.
The reasons that trigger and promote the change of chemical reagents can be roughly summarized as follows.
- to evaporate
Volatilization is the most common cause of reagent loss, concentration change, and specification drop of volatile reagents. The general characteristics of volatile reagents are: small molecular weight and low boiling point. Common inorganic reagents are: concentrated hydrochloric acid, concentrated nitric acid, oleum, etc., while organic reagents include liquid substances with fewer carbon atoms, such as methanol, ethanol, petroleum ether, gasoline, etc.
A class of reagents with sublimation properties is generally molecular crystals with less heat of sublimation. In the laboratory, there are generally two kinds of reagents (such as iodonaphthalene, etc.) sublimation at room temperature and reagents (such as sulfur and mercuric chloride) that are sublimated under heating conditions. The sublimation of such reagents mainly results in wastage and air pollution.
- Deliquescence and dilution
There are few chemical reagents that can deliquescence, most of them are soluble compounds, generally the anion radius is much smaller than the cation radius, and there are also anion and cation radius similar to the cation with more charge. After such reagents absorb water to form a saturated solution on the surface, if the pressure of the water vapor produced is less than the partial pressure of water vapor in the air, the deliquescence will continue until all the solutions are formed. Such as: sodium hydroxide, soda lime, etc., organic substances that are easily damp are sodium acetate, ammonium acetate, etc. Dilution refers to the phenomenon that the reagent solution absorbs moisture in the air, causing the concentration to decrease and become thinner. The reason is the same as deliquescence, which is caused by the external water vapor partial pressure being greater than the water vapor partial pressure of the reagent. Common reagents prone to dilution include concentrated sulfuric acid, orthophosphoric acid, ethylene glycol, etc.