Posting a Sample to a UK Lab: Packaging Instruction 650, the 50 g Limit and Who May Send

Royal Mail carries biological substances in Category B inside the UK only if they are sent by, or at the request of, a qualified medical practitioner, registered dental practitioner, veterinary surgeon, registered nurse or a recognised laboratory or institution; the total sample in any parcel is capped at 50 ml or 50 g; and the packaging must meet Packaging Instruction 650 ^[1]. Dry ice, liquid nitrogen and frozen water are on its prohibited list, including as coolants for these parcels ^[1].

The more useful fact for most readers is that a synthetic peptide sample is usually not a biological substance, so those rules do not apply to it at all. This page is the buyer's guide to posting: which rules your parcel meets, and what to do. The technical standard itself, with its pressure, drop and marking requirements, is a separate matter covered in the full Packaging Instruction 650 standard.

Which rules does your sample meet?

The Category B rules exist for human or animal material that may carry pathogens. Royal Mail's own wording describes the category as human or animal material including, but not limited to, excreta, secreta, blood and its components, tissue and tissue fluids ^[1]. UK transport guidance puts the duty to classify on the consignor, and treats material known not to contain infectious substances as outside the infectious-substance rules ^[2].

Marking a synthetic peptide sample UN3373 "to be safe" is a mistake, not a precaution. It declares the parcel to be something it is not, and it may route it into handling it did not need. Classify honestly, write down the basis, and pack for what the parcel actually contains.

If it is Category B: Royal Mail's conditions

Where you genuinely are sending biological material, for example a study sample to be tested for a peptide, Royal Mail allows it within the UK on four conditions ^[1].

1. Sender: it may only be sent by, or at the specific request of, a qualified medical practitioner, registered dental practitioner, veterinary surgeon, registered nurse or a recognised laboratory or institution.
2. Quantity: the total sample volume or mass in any parcel must not exceed 50 ml or 50 g.
3. Packaging: it must be posted in packaging that complies with Packaging Instruction 650.
4. Labelling: the sender's name and return address must be clearly visible on the outer packaging.

The sender condition is the one private buyers trip over. A private individual is not on the list. If a laboratory has asked you to send the material, that request is what brings the parcel within the rule, so keep it in writing. The 50 g cap is per parcel and counts total sample, not the weight of each tube.

Royal Mail separately allows exempt human or animal specimens returned in supplier sample kits, at the specific request of a medical professional or a recognised laboratory or institution, up to 250 ml or 250 g, in leakproof triple packaging marked "Exempt human specimen" or "Exempt animal specimen" ^[1]. That route is for kits a laboratory has supplied, and it is not a general alternative to Category B.

Keeping it cold without dry ice

Royal Mail's prohibited list includes dry ice and liquid nitrogen, naming them specifically when used as a coolant for UN3373 or other perishable items, and separately lists frozen water including packs of ice ^[1]. Its food-posting guidance points to gel packs instead ^[3]. In transport regulation dry ice is a dangerous good in its own right, which is why it needs trained shippers and venting packaging on the routes that accept it ^[2].

For most peptide samples the question does not arise. PeptideVerify, for instance, tells senders that powder samples can travel at ambient temperature with no cold pack, and suggests a cold pack for solutions only on journeys over 48 hours in warm weather ^[4]. A lyophilised vial on a next-day service is a short, dry trip. If a sample genuinely needs to stay frozen, the post is the wrong carrier; ask the laboratory which courier it uses for frozen receipts.

Posting an ordinary peptide sample

A chemical sample outside Category B is posted under ordinary parcel rules, which still prohibit several things that end up in laboratory parcels: flammable liquids, corrosive substances and compressed gases among them ^[1]. A peptide dissolved in a flammable solvent is prohibited on that ground alone, whatever else is true of it.

1. Read the receiving laboratory's instructions first. They override generic advice, and some specify the service.
2. Send the original sealed vial where the laboratory accepts it, so the label and batch reference travel with the sample.
3. Seal the vial in a bag, cushion it, and put the laboratory's order reference on the outside and the item reference on the vial ^[4].
4. Include the packing sheet or submission form inside the box.
5. Use the service the laboratory names. PeptideVerify recommends Royal Mail Tracked 24 for standard orders, and for endotoxin orders sent to its PO Box asks for Tracked 24 only, with no signature, and no Special Delivery, Signed For or courier ^[4].
6. Keep the proof of posting and the tracking number with your batch record.

That PO Box instruction is a good example of why the laboratory's own page comes first. A signed-for service sounds more careful, and in that case it would have been the wrong choice.

Couriers instead of the post

Couriers set their own terms, and they differ from Royal Mail's and from each other. PeptideVerify, for example, lists DPD, DHL, UPS and Evri as accepted for standard samples ^[4]. If you are sending anything unusual, a frozen sample or biological material, ask the courier's dangerous-goods or specialist desk before booking, and ask the laboratory which carrier it already receives from. A laboratory that takes frozen samples regularly will usually have a route it trusts.

The record that makes the result usable

A sample result is only as good as the link between the sample and the batch. Before posting, write down the batch reference, the vial taken, the date, who packed it and the tracking number, and keep a sealed sibling vial from the same batch. The handbook sets out what a chain-of-custody record should show once a sample is moving.

It also pays to know what a laboratory checks when a sample arrives. A leaking vial, a missing reference or a label that does not match the form can mean a sample is rejected or reported with a deviation noted, and either costs you a second posting.