Many biochemicals are robust once dry and properly stored, but some lose activity quickly when warm. Enzymes in glycerol, antibodies, certain nucleotides and some labile small molecules need controlled temperatures from the supplier's freezer to yours. International cold-chain shipping is more complex than ordinary freight, and most failures happen at predictable points.
Know the temperature the product actually needs
Start with the product's real requirement, not a default. Typical categories are:
- Ambient: many lyophilised powders and stable reagents.
- Refrigerated, 2 to 8 °C: many buffers, some enzymes and antibodies.
- Frozen, around minus 20 °C: many enzymes in glycerol, nucleotides and some standards.
- Deep frozen, minus 70 °C or below: some proteins, cells and particularly labile materials.
Shipping colder than necessary adds cost and can sometimes harm a product, for example by freezing an aqueous protein solution that should never be frozen.
Refrigerant options
Gel packs and phase-change materials
Conditioned gel packs keep contents in the 2 to 8 °C range for a limited time, typically one to three days depending on the shipper. They are not regulated as dangerous goods and are suitable for courier transport. Their weakness is duration, so delays quickly cause excursions.
Dry ice
Solid carbon dioxide sublimes at about minus 78.5 °C, keeping products frozen for several days if enough is packed. Dry ice is regulated for air transport as UN1845, Class 9, under a specific packing instruction. Packages must allow gas to escape, be marked with the net weight of dry ice, and carry the Class 9 label.
A less obvious issue: carbon dioxide can enter poorly sealed vials and acidify aqueous buffers, which may affect pH-sensitive products. Make sure vials are well sealed and consider secondary sealing.
Liquid nitrogen dry shippers
Dry shippers hold liquid nitrogen absorbed into a porous material, keeping contents near minus 150 °C or colder without free liquid. They are used for cells and very sensitive materials and are generally more expensive.
Where the cold chain usually breaks
- Weekend and holiday arrivals. A package that reaches the destination on a Friday evening may sit until Monday. Ship early in the week.
- Customs holds. Incomplete documents, unclear product descriptions or a missing permit can hold a package for days. Prepare invoices and declarations carefully, and describe biological materials accurately.
- Transfer points. Each change of carrier or aircraft is a chance for a box to sit on a warm tarmac.
- Last-mile delivery to a building where nobody signs for the package, or where it is left in a warm mailroom.
- Undersized refrigerant, chosen to save weight on air freight.
Planning a shipment
- Agree the temperature category and refrigerant with the supplier before ordering.
- Check whether your country requires an import permit for the material, especially anything of animal or microbial origin.
- Give the supplier a delivery address that is staffed, with a named recipient who knows the parcel is coming.
- Ask for tracking and arrange for the recipient to monitor it.
- For high-value or critical items, request a temperature data logger in the box.
For regular orders, ask the supplier for the expected transit time to your city and how much margin the chosen shipper provides. A shipper rated for 72 hours on a route that usually takes 48 hours leaves a reasonable buffer, while one rated for 48 hours on the same route leaves almost none.
Seasonal conditions matter too. Summer temperatures on hot tarmac and winter freezing during transit both put extra load on a shipper, so some suppliers adjust packaging by season.
What to check on arrival
- Refrigerant status. Is dry ice still present? Are gel packs still cold? Record it.
- Logger data, if included. Download it before discarding the box.
- Container integrity. Check for cracked vials or leaks.
- Labels and documents. Match the lot number with the certificate.
- Store immediately at the required temperature and log the time.
If refrigerant is gone or the logger shows an excursion, photograph the package and contact the supplier before using the product. Some materials tolerate brief excursions, and the supplier may have stability data to support a decision.
Documentation for cold-chain imports
Biological and temperature-sensitive materials attract more attention at customs than ordinary chemicals. A clear commercial invoice should describe each item specifically, for example "recombinant enzyme in glycerol buffer, for laboratory research use", rather than a generic phrase. Include the source, such as recombinant, plant or animal derived, if your country's import rules depend on it.
Some destinations require a veterinary or plant health permit for materials of animal or plant origin, or a declaration that a product contains no infectious agents. Obtain these before dispatch. A package held while a permit is arranged will rarely stay cold for long.
Choosing between one shipment and several
When an order mixes ambient, refrigerated and frozen items, consider splitting it. Packing everything with dry ice raises cost and can damage items that should not freeze. Separate shipments, each with the right refrigerant, are often safer and not much more expensive once volumetric weight is taken into account.
Handling after storage
Allow frozen vials to warm to room temperature before opening, to avoid condensation. Mix gently rather than vortexing proteins vigorously. Divide stock into single-use aliquots so you do not repeat freeze-thaw cycles, which damage many enzymes and proteins.
How Zemixal handles cold-chain items
Temperature requirements are shown on product pages in the Biochemicals division, and each lot ships with a certificate of analysis and SDS. Zemixal uses express courier for small temperature-sensitive packs and plans dispatch days around transit time to the destination. Check country notes on the ship to pages, and mention any permit requirements or delivery constraints when you contact us.