How to determine the validity period of chemical reagents

The expiration date of the reagent is an important factor affecting the accuracy of the experimental results. In actual use, people are always used to judging the effectiveness of chemical reagents by the production date, which is actually wrong. Unlike food and medicine, chemical reagents have a strict shelf life. Chemical reagents generally have no specific requirements and boundaries for shelf life. This is related to the fact that the shelf life of chemical reagents is affected by many factors; Judging whether the reagent has deteriorated and whether it can continue to be used. The influence of the properties of chemical reagents on the validity period Chemical reagents generally do not indicate the shelf life, and the determination of whether the reagents have deteriorated is mainly based on experience and comparison tests between old and new reagents. The validity period of chemical reagents varies greatly with the change of chemical properties of chemicals. In general, substances with stable chemical properties have longer shelf life and simpler storage conditions. Generally follow the following principles (general principles, not principles): Inorganic compounds, as long as they are properly kept and the packaging is intact, they can theoretically be used for a long time. However, it is easy to oxidize (such as sulfite, phenol, ferrous salt, iodide, sulfide, etc., and its solid or crystal should be sealed and stored, and it is not suitable for long-term storage; the aqueous solution of sulfurous acid and hydrogen sulfuric acid should be stored in a sealed container; potassium, sodium, and white phosphorus More importantly, liquid-sealed form) and deliquescent substances can only be stored for a short period of time (1 to 5 years) under dark, cool, and dry conditions, depending on whether the packaging and storage conditions meet the regulations. Organic low-molecular-weight compounds are generally highly volatile, and the airtightness of the packaging is better, so they can be stored for a long time (3 to 5 years). However, easily oxidized, thermally decomposed, easily polymerized, and photosensitive substances, etc., can only be stored for a short period of time (1 to 5 years) in dark, cool, and dry conditions, depending on whether the packaging and storage conditions meet the regulations. Organic polymers, especially life materials such as oils, polysaccharides, proteins, enzymes, and polypeptides, are easily affected by microorganisms, temperature, and light, and lose their activity. In principle, reference substances, standard substances and high-purity substances should be stored in strict accordance with the storage regulations to ensure that the packaging is intact and avoid being affected by the chemical environment, and the storage time should not be too long. Generally, reference substances are used within the validity period. The storage time at room temperature (15ºC~25ºC) generally does not exceed 2 months. More than two months to re-calibrate or check before use. Culture medium: Prepare and sterilize the medium according to regulations, cool to room temperature, and store in a dark place (store in the refrigerator as much as possible). The prepared medium should be used up within one month. Unless otherwise specified, the validity period of test solution, buffer solution and indicator (solution) is half a year. The mobile phase and purified water used in the liquid phase are valid for 15 days. Unless otherwise specified, liquid reagents are valid within one year after opening, and solid reagents are valid within three years after opening. The effect of the storage environment of chemical reagents on the validity period 1. The influence of air: the oxygen in the air is easy to oxidize and destroy the reducing reagents. Strong alkaline reagents are easy to absorb carbon dioxide and turn into carbonates. Moisture can make some reagents deliquescence and agglomerate; fibers and dust can make some reagents reduce and change color. 2. The influence of temperature: The speed of reagent deterioration is related to temperature. High temperature in summer will accelerate the decomposition of unstable reagents; severe cold in winter will promote the polymerization of formaldehyde and precipitate deterioration. 3. The influence of light: Ultraviolet rays in sunlight can accelerate the chemical reaction of certain reagents and cause them to deteriorate (such as silver salts, mercury salts, potassium, sodium, ammonium salts of bromine and iodine, and certain phenolic reagents). 4. The influence of impurities. Whether the unstable reagent is pure or not, and its influence on its deterioration cannot be ignored. 5. Effect of storage period. Unstable reagents may undergo 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, and mildew, 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. The impact of the use requirements of chemical reagents on the validity period The validity period of chemical reagents is judged according to the requirements of use. The important point is to judge whether the reagents have an impact on the results. If there is an impact, the validity period needs to be shortened or even scrapped.