How to determine the expiry date of the reagent
The effective date of the reagent is an important factor that affects the accuracy of the experimental results. In actual use, people are always accustomed to judging the effectiveness of chemical reagents by the production date, but this is actually wrong.
Chemical reagents do not have strict shelf life like food and drugs. Chemical reagents generally do not have specific requirements and limits for shelf life. This is related to the fact that the shelf life of chemical reagents is affected by many factors; it should be based on chemical properties, storage conditions, etc., and combined with the actual work. Circumstances determine whether the reagent has deteriorated and whether it can be used continuously.
The effect of the nature of the reagent on the expiration date
The shelf life of chemical reagents is generally not indicated. The determination of whether a reagent has deteriorated is mainly based on experience and a comparison test between new and old reagents.
The validity period of chemical reagents varies greatly with the change of the chemical properties of chemicals. Under normal circumstances, chemically stable substances have a longer shelf life and simpler storage conditions.
Generally follow the following principles (general principles, not absolute principles):
Inorganic compounds, as long as they are properly stored and the packaging is intact, they can theoretically be used for a long time. But it is easy to be oxidized (such as sulfite, phenol, ferrous salt, iodide, sulfide, etc.). The solid or crystal should be sealed and stored, and it is not suitable for long-term storage; aqueous sulfurous acid and hydrogen sulfuric acid solutions should be sealed and stored; potassium, sodium, white phosphorus It is more necessary to use liquid-sealed form), easily deliquescent substances, in the dark, cool and dry conditions, can only be stored for a short period of time (1 to 5 years), depending on whether the packaging and storage conditions meet the requirements.
Organic low-molecular-weight compounds are generally more volatile, and the airtightness of the packaging is better, and they can be stored for a long time (3 to 5 years). However, it is easy to oxidize, decompose by heat, easily polymerize, and photosensitive substances. They 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 requirements.
Organic polymers, especially life materials such as oils, polysaccharides, proteins, enzymes, and peptides, are extremely susceptible to the effects of microorganisms, temperature, and light, and lose their activity or deteriorate. Therefore, they must be stored in cold storage (frozen). Shorter.
In principle, reference materials, standard materials and high-purity materials should be stored in strict accordance with the preservation regulations to ensure that the packaging is intact, avoid being affected by the chemical environment, and the storage time should not be too long. In general, the reference substance must be used within the validity period. The storage time under normal temperature (15ºC~25ºC) generally does not exceed 2 months. More than two months must be re-calibrated or checked before use.
Medium: Prepare and sterilize the medium according to the 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 1 month.
Unless otherwise specified, the validity period of the test solution, buffer solution, and indicator (liquid) is half a year.
The mobile phase and purified water for the liquid phase are valid for 15 days.
Unless otherwise specified, liquid reagents are valid for one year after opening, and solid reagents are valid for three years after opening.
Environmental conditions affect the validity period
The influence of air: The oxygen in the air is easy to oxidize and destroy the reducing agent. Strong alkaline reagents can easily absorb carbon dioxide and become carbonate. Moisture can deliquify and agglomerate some reagents; fiber and dust can reduce or change color of certain reagents.
Influence of temperature: The rate 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 precipitation deterioration.
Influence of light: ultraviolet rays in sunlight can accelerate the chemical reaction of certain reagents and make them deteriorate (such as silver salt, mercury salt, potassium, sodium, ammonium salt of bromine and iodine, and certain phenolic reagents).
The influence of impurities. The purity of unstable reagents and the influence of their deterioration cannot be ignored. For example, pure mercury bromide is actually not affected by light, while mercury bromide containing trace amounts of mercury bromide or organic impurities tends to turn black when exposed to light.
The effect of shelf life. Unstable reagents may undergo disproportionation polymerization, decomposition or precipitation after long-term storage. If abnormal phenomena such as delamination, turbidity, discoloration, and mold are found in the liquid during the storage period and the validity period, when the mobile phase is used for sample detection, the retention time or relative retention time of the sample changes significantly, and the solids such as moisture absorption, discoloration, etc. Abnormal phenomena should stop using.
Effect of use on expiry date
The validity period of the chemical reagent is judged according to the requirements of use. The most important point is to judge whether the reagent has any influence on the result. If there is an influence, the validity period needs to be shortened, or even scrapped.