Everything you need to know
The short answer is no, and the reason is the content result. A laboratory that reports milligrams per vial has to dissolve the whole vial to measure it. Here is what happens to each vial you send, what the lab keeps, and how to hold back a sample of your own.
Do I get my vial back after testing?
No. The vial used for the HPLC work is reconstituted whole, so there is no dry powder left to return. Content in mg per vial is measured by dissolving the entire vial in a known volume and comparing it with a reference standard; a lab that returned your vial could not have reported that number. The identity and purity results come from the same solution. What remains at the end is a small volume of peptide solution, not the sealed product you shipped.
What happens to the solution after the test?
It is kept as the laboratory retain for a period after the certificate is issued, labelled with the sample ID, and stored refrigerated. The retain exists so a result can be re-injected if a question comes up during review, for example a second injection to confirm an identity call. It is not a product and is not returned to the customer. Peptides degrade in solution, so a retain is only meaningful for a short window; after that it is discarded.
What about the vials on an injectable safety panel?
All of them are used. Tier 2 and Tier 3 take three vials, each with one job. One is reconstituted for identity, purity and content. One is opened aseptically for microbiology (bioburden on Tier 2, USP <71> sterility on Tier 3) and endotoxin; sterility testing uses the entire contents of the container, so nothing comes back from it. One goes intact to heavy metals, where it is digested in acid for ICP-MS. Nothing physical returns from any of the three. How much material each panel needs.
How do I keep a sample for myself?
Send one vial more than the panel needs and keep the rest of the lot sealed at home. If you want the lab to hold an unopened vial from the same lot for later comparison, that is a conformity vial, listed on the pricing page, and it has to be requested at submission so it is logged in and stored rather than opened. A request for a retain after the work has started cannot be met, because by then the material is in solution. Conformity vials on the price list.
Can you test part of a vial and send the rest back?
Not if you want a content result. Weighing out a portion of a lyophilized cake is not a reliable way to measure what was in the vial, because fill weights vary and the powder is mostly bulking agent. A partial sample can still be tested for identity and purity, with content reported as not determined, but the opened vial is no longer a product anyone should use, so there is little point returning it. The cleaner choice is a whole vial for the lab and a sealed vial for you.
Does the certificate note what was consumed?
The certificate records the sample ID, the label claim, the recorded reconstitution volume, and the lot and lab IDs that tie the result to the vial received, and the chain-of-custody record shows the date of receipt and the condition of the vial. That is the evidence that the result belongs to the vial you sent, which is the reason most people ask about the vial in the first place. What a peptide COA shows.