There is no fixed deadline for the validity of reagents, but this information can serve as a reference

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Factors affecting the expiration date of reagents: The expiration date of reagents is an important factor that influences the accuracy of experimental results. In practical use, people tend to rely on the production date to determine the validity of chemical reagents, but this is incorrect. Chemical reagents do not have strict expiration dates like food and drugs; generally, there are no specific requirements or limits regarding their expiration dates, and this is because the expiration date of chemical reagents is influenced by various factors ； It is necessary to determine whether the reagent has deteriorated and can still be used by considering its chemical properties, storage conditions, as well as the actual circumstances of use. The effect of reagent properties on shelf life: Chemical reagents generally do not have an indicated expiration date; determining whether a reagent has deteriorated relies mainly on experience and by comparing it with new reagents. The shelf life of chemical reagents varies greatly depending on the chemical properties of the substances. Generally, the more stable a substance is chemically, the longer its shelf life, and the simpler its storage conditions. Generally, the following principles are followed (these are general principles, not absolute ones): 1. Inorganic compounds, provided they are stored properly and their packaging remains intact, can theoretically be used for a long time. However, they are prone to oxidation (subsulfites, phenols, ferrous salts, iodides, sulfides, etc. should be stored in sealed solid or crystalline form, as long-term storage is not advisable) ； Aqueous sulfurous acid and hydrosulfuric acid solutions should be stored in sealed containers ； Potassium, sodium, and white phosphorus (which must also be stored in a liquid-sealed format), as well as substances that are prone to deliquescence, can only be stored for a short period of time (1–5 years) under conditions of darkness, coolness, and dryness; the exact storage duration depends on whether the packaging and storage conditions meet the specified requirements. 2 Organic small-molecular-weight compounds are generally highly volatile; therefore, the packaging must be airtight to allow for long-term storage (3–5 years). However, substances that are prone to oxidation, thermal decomposition, polymerization, or are photosensitive can only be stored for a short period of time (1–5 years) under conditions of darkness, coolness, and dryness; the exact storage duration depends on whether the packaging and storage conditions meet the specified requirements. 3 Organic polymers, especially biological materials such as fats, polysaccharides, proteins, enzymes, and peptides, are highly susceptible to the effects of microorganisms, temperature, and light, which can cause them to lose their activity or deteriorate. Therefore, they need to be stored in a refrigerated (frozen) condition, and for only a short period of time. 4. Reference materials, standard materials, and high-purity substances should, in principle, be stored in strict accordance with the specified storage rules, to ensure that their packaging remains intact and to prevent them from being affected by the chemical environment; moreover, they should not be stored for too long. Under normal circumstances, reference materials must be used within their expiration date. The storage time at room temperature (15°C~25°C) is generally no more than 2 months. It needs to be recalibrated or inspected after more than two months before it can be used again. 5 Medium: Prepare the medium as specified and disinfect it, then allow it to cool to room temperature. Store it in a dark place (preferably in a refrigerator), and the prepared medium should be used within 1 month. 6 Unless otherwise specified, the shelf life of test solutions, buffers, and indicators (liquid) is six months. The flow phase for the liquid phase and purified water have a validity period of 15 days. 7 Unless otherwise specified, liquid reagents are valid for one year after opening, while solid reagents are valid for three years after opening. Effect of environmental conditions on shelf life 1 Effect of air: Oxygen in the air can easily oxidize reducing agents, thereby damaging them. Strongly alkaline reagents readily absorb carbon dioxide and turn into carbonates, while moisture can cause certain reagents to deliquesce and clump together ； Fibers and dust can cause certain reagents to be reduced or change color, etc. 2 Effect of temperature: The rate at which reagents deteriorate is related to temperature. High temperatures in summer accelerate the decomposition of unstable reagents ； The severe cold in winter causes formaldehyde to polymerize, precipitate, and deteriorate. 3 Effect of light: The ultraviolet rays in sunlight can accelerate the chemical reactions of certain reagents, causing them to deteriorate (such as silver salts, mercury salts, potassium, sodium, and ammonium salts of bromine and iodine, as well as certain phenolic reagents). 4 Influence of impurities. The purity of unstable reagents and its impact on their degradation cannot be ignored. For example, pure mercury bromide is actually unaffected by light, whereas mercury bromide containing trace amounts of mercurous bromide or organic impurities darkens easily when exposed to light. 5 Impact of storage period. Unstable reagents may undergo changes such as disproportionation polymerization, decomposition, or precipitation after long-term storage. If abnormalities such as stratification, turbidity, discoloration, or mold formation are observed in liquids during storage and within their shelf life, or if the retention time or relative retention time of samples changes significantly when the mobile phase is used for sample testing, then solid materials should be discontinued from use if abnormalities such as moisture absorption or discoloration are detected. Determining the shelf life of chemical reagents is based on the requirements for their use. The most important factor is to assess whether the reagent has an impact on the results; if it does, the shelf life needs to be shortened, or even the reagent should be discarded.