A chemical that met its specification on the day it was made can drift out of specification on a laboratory shelf, and a poorly organised store can turn a minor spill into a fire or toxic release. Good storage practice serves two purposes: safety and quality. This article covers both, with practical rules you can apply in any laboratory.
Start with the SDS and label
Section 7 of the Safety Data Sheet gives storage conditions and incompatibilities, and Section 10 describes stability and conditions to avoid. The label and COA usually state the recommended storage temperature and any special requirements, such as protect from light or store under inert gas. These documents should be the starting point for every storage decision.
Segregate by hazard, not alphabetically
Alphabetical storage is convenient but dangerous, because it can place incompatible chemicals side by side. Store by hazard class instead, with physical separation or secondary containment between incompatible groups.
| Group | Keep away from | Notes |
|---|---|---|
| Flammable liquids | Oxidisers, ignition sources | Use a flammable storage cabinet. Limit quantities outside it |
| Oxidisers | Flammables, organics, reducing agents | Nitrates, peroxides, permanganates, perchlorates |
| Inorganic acids | Bases, cyanides, sulfides, reactive metals | Separate oxidising acids such as nitric and perchloric acid from organic acids |
| Bases | Acids, some metals such as aluminium | Store below eye level |
| Water-reactive substances | Water, aqueous solutions, sprinklers where possible | Alkali metals, hydrides, some metal powders |
| Toxics | General access | Locked, ventilated storage for highly toxic materials |
Temperature
- Ambient usually means 15 to 25 °C, or up to 30 °C in some specifications. Avoid direct sunlight and heat sources.
- Refrigerated means 2 to 8 °C. Flammable materials must be stored only in refrigerators designed for flammables, since domestic refrigerators contain ignition sources.
- Frozen is typically −20 °C, or −70 to −80 °C for sensitive biochemicals.
Allow refrigerated and frozen containers to reach room temperature before opening, or moisture from the air will condense onto the contents.
Moisture, air and light
Hygroscopic substances, such as anhydrous salts, sodium hydroxide and many APIs, absorb water from the air, which changes their effective assay and can cause caking or hydrolysis. Keep containers tightly closed, reseal promptly and use desiccators for critical materials. Air-sensitive reagents, such as organometallics and some phosphines, need inert atmosphere storage and septum-sealed bottles. Light-sensitive materials, including silver salts, many vitamins and some solvents, should be kept in amber glass or opaque containers.
Peroxide-forming chemicals
Some solvents and reagents react slowly with atmospheric oxygen to form organic peroxides, which can explode when concentrated by evaporation or distillation. Common peroxide formers include:
- Diethyl ether, diisopropyl ether and tetrahydrofuran
- 1,4-Dioxane and some glycol ethers
- Certain alkenes and dienes, such as cyclohexene
Good practice: buy in quantities that will be used quickly. Date containers on receipt and on opening. Prefer stabilised grades where the stabiliser does not interfere. Test for peroxides periodically after opening, commonly every 3 to 12 months depending on the compound. And never distil to dryness. Diisopropyl ether is particularly hazardous and is avoided by many laboratories.
Other chemicals that change hazardously with age
- Picric acid and some other polynitro compounds become shock-sensitive when they dry out. They are supplied wetted with water, which must be maintained.
- Formic acid can slowly decompose to carbon monoxide, building pressure in sealed bottles.
- Hydrogen peroxide decomposes slowly, releasing oxygen. Containers have vented caps.
Shelf life, retest and expiry dates
A retest date indicates when a material should be re-examined to confirm it still meets specification. It does not mean the material becomes unusable on that date. An expiry date is a firm limit after which the material should not be used. Both assume unopened storage under the stated conditions.
Once a container is opened, stability can change. Many laboratories set in-house rules for opened reagents, for example assigning a shorter use period to hygroscopic or oxidation-sensitive materials, and recording the opening date on the label. For regulated laboratories, these rules should be documented in procedures.
| Material type | Typical stability consideration |
|---|---|
| Inorganic salts, anhydrous | Very stable if kept dry. Hygroscopicity is the main risk |
| Common organic solvents | Stable. Water uptake and peroxide formation for some |
| Standard solutions | Concentration changes by evaporation, adsorption or reaction. Restandardise |
| Biochemicals and enzymes | Temperature-sensitive. Freeze-thaw cycles degrade activity |
| Reference standards | Follow supplier storage exactly. Track retest dates |
Inventory management
- Keep a live inventory with location, quantity, received date, opened date and retest or expiry date.
- Use first-expired, first-out rather than first-in, first-out when lots have different dates.
- Review the inventory regularly and dispose of expired, unlabelled or degraded materials through proper waste routes.
- Avoid stockpiling. Smaller, more frequent purchases often cost less once waste is counted.
Containers and labels
Keep chemicals in their original containers where possible. If you transfer material, use a compatible container and label it with the name, concentration, hazard pictograms, date and your initials. Never store chemicals in food or drink containers. Replace damaged labels promptly.
FAQs
Does a chemical become unusable after its retest date?
Not necessarily. A retest date means the material should be re-examined. If it still meets specification, it can often be used for a further defined period.
Can flammable solvents be stored in a normal refrigerator?
No. Domestic refrigerators contain ignition sources. Use a refrigerator specifically designed and rated for flammable materials.
How often should peroxide formers be tested?
It depends on the compound and local procedures, but testing every 3 to 12 months after opening is common, and always before distillation or evaporation.