Storage, transit and retest of research peptide raw material

This guide is written for the person who signs for the parcel and keeps the stock book: a laboratory manager, a purchasing officer or a distributor holding several lots at once. It is about the material as an object in your inventory. It does not describe what any compound does, and it gives no instructions for use. Where it mentions a chromatogram, it means the one on the batch certificate and the one you may commission later to compare against it.

What lyophilized means and why material ships that way

Lyophilization is freeze-drying. The material is dissolved, frozen and held under vacuum so that the ice leaves as vapour without passing through liquid water. What remains is a dry solid with a very low water content: in a vial, a porous cake or a loose powder at the bottom; in a bulk container, a weighed powder. The peptide is the same molecule it was in solution. What has changed is that the water that would let it hydrolyse, aggregate or move around is gone.

That is why material ships this way. A dry solid is far less reactive than a solution, so it tolerates the hours or days of transit, and a brief temperature excursion, better than a liquid would. A solid can also be weighed, which is what makes a bulk order of raw powder possible: the net mass on the container is a number you can check on your own balance. The guide on lyophilized vials versus raw powder covers how buyers choose between the two formats. Lyophilized material is not inert, though. It still responds to heat, light, moisture and oxygen, only slowly, and the slowness depends on how it is kept.

What a cake looks like and what it does not tell you

A vial cake can be a neat white plug, a plug that has pulled away from the glass, a cracked plug or a loose powder, depending on the fill mass, the excipient and the freeze-drying cycle. None of those appearances is a quality result; the chromatogram on the certificate is the measure of the lot. What is worth noting is anything that suggests the seal has failed: visible liquid, a cake collapsed into a glassy film, a strong colour change, or a stopper that sits proud of the neck. Photograph it and raise it against the lot number before the vial is opened.

Cold-chain transit for powder orders and what to check on arrival

Raw powder orders are packed cold-chain: the sealed powder container sits inside an insulated carton with refrigerant packs, and the carton is the unit the courier handles. The point is to hold the material cold for the length of the journey and to keep the outer environment away from the inner container. Vial kits are a smaller mass of material; the quotation states the packing that applies to your route.

The arrival check takes a few minutes and is done before the inner packaging is opened, with the quotation and the batch certificate to hand. Photograph each step; the photographs are what a mismatch is later resolved against. The guide on matching a COA to the batch you receive covers the paperwork side.

If the refrigerant has thawed

A thawed pack is not on its own evidence that anything has happened to the material. The powder is a dry solid, the insulated carton slows the rise in temperature long after the packs have thawed, and the transit time is a small fraction of the time the lot will spend in your store. What a thawed pack does mean is that the transit should be written down: hours in transit, the indicator state if there is one, and the condition of the packs. The record then shows whether your own excursion limit was exceeded. Move the container into cold storage at once, not after the paperwork is filed.

Unopened storage: cold, dark, closed and dry

The storage conditions for unopened lyophilized material are the same four words for every compound on this site: cold, dark, closed and dry. They are not instructions for use. They are the conditions under which a sealed vial or a sealed powder container changes most slowly, and they are what the retest date on the certificate assumes. This guide gives no temperature figure; the figure that applies is the one on the certificate and in your own quality system, and it can be asked for against a lot number on the RFQ channel.

Cold slows every chemical process in the solid. Dark matters because some amino acid residues absorb light, and the products show up later as extra peaks in a chromatogram. Closed means the original stopper and cap, or the original container seal, stays in place until the material is needed; every opening lets in air and the moisture it carries. Dry means the secondary packaging and any desiccant stay around the container, because a cold store is a humid place and condensation forms on anything colder than the air around it.

Keep the material in its secondary packaging, label side outward, in a position reserved for it and written in the inventory record: not in a door shelf that warms each time the unit is opened, and not beside reagents that fume or leak. Nothing here covers an opened container or material taken into solution; those depend on your own procedure.

What a retest date is, and what it is not

A retest date is the date by which material still in stock should be re-examined before it is used further. It is set by the manufacturer at release and printed on the certificate of analysis beside the manufacturing date and the test date. Pepti batch records carry all three dates, and the public records in the Pepti COA library show a retest date two years after manufacture.

A retest date is not an expiry date. An expiry date says the material should not be used after it; a retest date says the material should be examined again before it is used after it. A lot past its retest date is therefore not written off but held, re-examined, and then either returned to stock with a new internal retest date or withdrawn. The decision is made on a new chromatogram, not on the calendar.

A retest date is also not a stability claim for every condition. It assumes the container is unopened and has been kept cold, dark, closed and dry. It says nothing about a vial that has been opened, a powder that has been decanted, or material that has spent a week on a bench. For those, the relevant date is the date of the event, and the relevant record is yours.

• Manufacturing date: when the lot was made. The retest date is counted from here.
• Test date: when the chromatogram and the mass spectrum on the certificate were run. The purity result belongs to this date.
• Retest date: the date by which held material should be examined again. On the public Pepti records it falls two years after manufacture.

How to log receipt date, lot, retest date and location

The inventory record is the document that lets you answer, months later, which lot a given vial came from, when it arrived, where it has been and when it is due for re-examination. One line per lot, not per order and not per vial, is the right granularity; a mixed order of powder and a vial kit is two lines because it is two lots.

Make the record on the day the parcel is opened, by the person who did the arrival check, from the label and the certificate rather than from memory. Copy the lot number character by character. Copy the retest date from the certificate for this lot, not from a previous lot of the same compound. Write the storage position as a location another person could walk to. A spreadsheet is enough, provided the record exists before the first vial is withdrawn and the retest date sits in a column that can be sorted.

What re-examination means in practice

Re-examination means running a new chromatogram on the held material and comparing it with the chromatogram on the original certificate. In practice that is an HPLC purity run under the same or an equivalent method, usually with a mass-spectrometry identity check alongside it so that the main peak is confirmed as the same molecule. The result is a new purity figure and a new set of impurity peaks, read against the figures on the certificate for the same lot.

There are two ways to get it done. The manufacturer can re-examine a retained sample or a unit you send back; ask on the RFQ channel whether that is offered for the lot in question and what it needs from you. Or an outside laboratory can do it on your own account: you send a sealed vial or a weighed portion of powder with the lot number and a copy of the original certificate, and you receive a report that cites the lot. Either way the lot number is the thread that ties the new result to the old one.

What you are looking for is agreement. A main-peak purity close to the original figure, with no new peaks, means the material has not changed within the resolution of the method. A lower main-peak area with new peaks means something has happened, and the inventory record should tell you what. This guide sets no threshold for agreement; that belongs in your own quality procedure. Send a sealed unit where you can, since an opened vial tells you about the opened vial and not about the lot, and keep one sealed unit in reserve so that a later question can still be answered on unopened material.

The handling errors that most often change a chromatogram

Most changed chromatograms trace back to handling, not to the material as made. The four errors below account for most of them, and all four are visible in a good inventory record, which is the main reason to keep one.

• Repeated warming and cooling of an opened container. Each time a cold container is opened in a warm room, moisture condenses on the solid, and each time it goes back into the cold that moisture stays. The signature is a loss of main-peak area and new peaks from hydrolysis.
• Light. A vial left on a lit bench, or on an open shelf under a lamp, is exposed to light that some residues absorb. The signature is small new peaks near the main peak that grow with time.
• Moisture ingress. A stopper lifted and reseated, a cap loosened, or a powder container opened in a humid room all let water in. The signature is the same as for warming and cooling, because the mechanism is the same.
• Decanting. Splitting a powder lot into sub-containers exposes the whole lot to air once, adds a weighing step, and creates containers whose labels are written by hand. The chromatographic signature is modest; the inventory signature is a lot that can no longer be traced to a single sealed container.

Decanting and sub-lots, if you must

If a 5 g powder order has to be split, split it once, on arrival, cold and in a dry area, into containers that are sealed at once. Label each with the parent lot number as printed, the net weight it holds and the day it was split, and enter each as a line under the parent lot. Do not split again later, and do not combine remainders. Two errors break the record outright: mixing two lots in one container, which leaves a mixture with no lot number, and storing a container without its lot label.

Stock rotation across lots, and lots past their retest date

Where you hold more than one lot of a compound, rotate by retest date rather than by receipt date. The lot nearer its retest date is used first, even if it arrived later. This is where the sortable retest-date column in the inventory record earns its keep: sort by it, and the order of use falls out.

Keep one lot open per compound at a time where you can, so that the sealed lots stay sealed and the open one is the only one that accumulates handling. When a new lot arrives, read its certificate against the one you already hold: same CAS number, same method, and a retest date later than the lot in use. If the new lot has an earlier retest date, which can happen with allocated stock, it goes to the front of the queue.

When a held lot passes its retest date

A lot that passes its retest date is not spoiled; it is unexamined since the test date on its certificate. Move it to a marked quarantine position so that it is not withdrawn by habit, mark the inventory line, and decide between three options: re-examine it, by the manufacturer or an outside laboratory, and return it to stock with an internal retest date if the new chromatogram agrees with the original; withdraw it and dispose of it under your own procedure; or hold it in quarantine as a comparison until a new lot on order has been checked, then withdraw it. What should not happen is that the lot stays on the shelf, unmarked, and is used because it was there. The retest date exists to force a decision, and the inventory record is where the decision is written.

What Pepti publishes, and what it does not claim

Pepti publishes batch records in its own public COA library, and the batch table on each compound page mirrors them. Each record carries the product name, the fill, the lot alias, an HPLC purity result, a mass-spectrometry identity result, and the manufacturing, test and retest dates. The record for a lot you are quoted can be read before you pay, and the lot number on the container you receive is matched to it on arrival. The quality page sets out what the records show and what they do not.

Pepti does not publish a storage-stability study for each lot, and the retest date is not one. It is the date by which held material should be re-examined, under the conditions described above, and nothing more. The records say what a lot was on its test date; what it is on the day you re-examine it depends on how it was kept, which is why this guide is about your record rather than the manufacturer's. No certificate or registration is claimed on this site. Nothing on this page is an instruction for use; material is supplied for research use only.