The validity period of reagents is an important factor affecting the accuracy of experimental results. In the actual use process, people are always used to judging the effectiveness of chemical reagents by the date of production, but it is not. Different from food and medicine, chemical reagents have no strict shelf life and no specific requirements and boundaries, which is related to the influence of many factors on the shelf life of chemical reagents. But it mainly changes because of its nature and application. Therefore, the chemical reagent should be properly preserved, and then combined with the actual situation of work, whether the reagent is deteriorated, whether it can be used continuously or take appropriate measures to purify it.
Chemical reagents have no shelf life, and it is mainly based on experience and comparative tests between old and new reagents to judge whether the reagents are deteriorating. To understand the physical and chemical properties of chemical reagents, the validity of chemical reagents varies greatly with the chemical properties of chemicals.
Generally speaking, the longer the shelf life of chemically stable substances, the simpler the storage conditions. To preliminarily judge the stability of a substance, you can follow the following principles.
Theoretically, inorganic compounds can be used indefinitely as long as they are properly preserved and packaged. However, those that are easily oxidized (such as sulfite, phenol, ferrous salt, iodide, sulfide, etc. ) should be sealed and stored, and should not be stored for a long time; Sulfuric acid and sulfuric acid aqueous solution should be sealed and preserved; Potassium, sodium and white phosphorus should be sealed in liquid form) and deliquescent substances can only be stored in dark, cool and dry conditions for a short time (1 ~ 5 years), depending on whether the packaging and storage conditions meet the requirements.
Organic small molecular weight compounds are generally volatile, and the packaging is airtight, which can be stored for a long time (3 ~ 5 years). However, substances that are easily oxidized, decomposed by heat, polymerized and exposed to light can only be stored in dark, cool and dry conditions for a short period (1 ~ 5 years), depending on whether the packaging and storage conditions meet the requirements. Organic polymers, especially biological materials, such as oils, polysaccharides, protein, enzymes, peptides, etc. It is easily influenced by microorganisms, temperature and light, so it loses its activity or spoils. Therefore, they should be stored in cold storage (freezing) for a short time.
In principle, reference materials, reference materials and high-purity materials should be kept in strict accordance with the preservation 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 speaking, reference materials must be used within the validity period. GB/T 60 1-2002 clearly stipulates the validity period of standard solution: at normal temperature (15? C~25？ C) The storage time is generally no more than 2 months. After more than two months, it should be recalibrated or checked before use.
Culture medium: Prepare the culture medium according to regulations, disinfect it, cool it to room temperature, and store it away from light (try to put it in the refrigerator). The prepared culture medium should be used up within one month. For details, please refer to Operating Procedures for Medium Preparation. Unless otherwise specified, the validity period of test solution, buffer solution and indicator (liquid) is half a year. The validity period of HPLC mobile phase and purified water is 15 days.
The reagent used for inspection and the prepared test solution must be labeled, and the preparation record of the prepared test solution must be made, including the use record of the culture medium, and the use record should be made after the standard titration solution is collected. The validity period of the test reagent must be within the storage period. Unless otherwise specified, liquid reagents are valid within one year after opening and solid reagents are valid within three years after opening.
There are no specific requirements and restrictions on the shelf life of chemical reagents. The management of chemical reagents usually needs "appropriate" storage and "eight precautions" (anti-volatilization, moisture-proof, anti-deterioration, anti-poisoning, anti-light, anti-impact, anti-rat and fire prevention). Deterioration of reagents is one of the main causes of analysis errors, and it is easy to cause deterioration of reagents under the following circumstances:
(1) air impact.
Oxygen in the air easily oxidizes the reducing agent and destroys it. Strong alkaline reagents easily absorb carbon dioxide and become carbonate, and moisture can deliquesce and agglomerate some reagents; Fiber and dust can reduce and discolor some reagents.
(2) The influence of temperature.
The rate of reagent deterioration is related to temperature. High temperature in summer will accelerate the decomposition of unstable reagents; The severe cold in winter promotes the polymerization and precipitation of formaldehyde.
(3) the influence of light.
Ultraviolet rays in sunlight can accelerate the chemical reaction of some reagents and make them deteriorate (such as silver salts, mercury salts, ammonium salts of potassium, sodium, bromine and iodine and some phenolic reagents).
(4) Influence of impurities.
Whether the unstable reagent is pure or not and its influence on its deterioration can not be ignored. For example, pure mercury bromide is actually unaffected by light, while mercury bromide containing a small amount of mercurous bromide or organic impurities tends to turn black under light.
(5) Influence 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 be layered, turbid, discolored and moldy, the retention time or relative retention time of the sample will change obviously when the mobile phase is used for sample detection. If the solid is found to be hygroscopic and discolored, it should be stopped.
The stability of most chemicals is relatively good, and the specific situation should be judged according to the actual use requirements. If the analysis data is taken as a general understanding, or the analysis results have no specific and accurate requirements, such as general teaching experiments, the quality level of chemical reagents can generally be required. However, the factory test data is used to guide production, and the quality index of chemical reagents must not be vague. In most cases, the chemical reagents used for general synthetic preparation can be satisfied with industrial-grade chemical reagents. However, in some cases, the quality requirements of research and some special chemicals are very strict and need to be strictly controlled. Reagents with long shelf life can be used for detection tasks with low requirements, and reagents that may deteriorate can be compared with newly purchased reagents to determine whether they deteriorate. As long as the chemical properties are unchanged and impurities are not introduced, it can be used in principle.