Peptide degradation: how storage and shipping change what a lab test finds

What peptide degradation is

Peptide degradation is the chemical or physical change of a peptide into related molecules over time. The main pathways are oxidation, deamidation, cleavage of the chain by water (hydrolysis), ring formation at the start of the chain, and aggregation. A Ghent University review of peptide medicines adds β-elimination, diketopiperazine and succinimide formation, and keeps these apart from synthesis impurities such as missing amino acids.

On a lab report, the peptide degradation process leaves three signs. HPLC purity falls as impurity peaks grow. LC-MS finds masses shifted by a known step. Content per vial falls. Water content by Karl Fischer titration shows how much moisture the powder holds, and moisture is one of the main causes.

This guide covers peptide products in vials. Enzymes breaking peptides down in cells or in the body are a separate subject.

Peptide degradation chart: pathways, mass shifts and signs

Pathway	What changes	Sites most at risk	LC-MS sign	HPLC sign
Oxidation	An oxygen atom is added to a side chain	Met, Trp, Cys	+16 Da per oxygen, +32 Da for two	New peaks; in one semaglutide study a Trp-oxidised form eluted before the main peak
Deamidation	A side-chain amide becomes an acid	Asn, especially before Gly; Gln	+0.984 Da, inside the isotope pattern	Peaks close to the main peak
Isomerisation and racemisation	Asp becomes isoAsp; L-forms become D-forms	Asp, and Asn through deamidation	None: same mass	Seen only if the method separates them
Hydrolysis	The backbone breaks	Backbone bonds; faster with heat and water	Fragments lighter than the peptide	New peaks; mg per vial falls
Pyroglutamate formation	An N-terminal Gln or Glu closes into a ring	N-terminal Gln or Glu	−17 Da from Gln, −18 Da from Glu	A new peak
Aggregation	Molecules join into dimers and larger forms	Depends on sequence and moisture	Covalent dimers carry about twice the mass	Reversed-phase HPLC may not show them; size-exclusion chromatography (SEC) is the usual tool

Bachem’s handling guide says peptides that contain Asn, Gln, Met, Cys or Trp have limited shelf lives. Sequence matters too. In 1987, Geiger and Clarke showed that a model peptide with an Asn-Gly pair deamidated with a half-life of only 1.4 days in a pH 7.4 solution at 37 °C. Replacing the glycine with leucine or proline slowed the reaction 33 to 50 times. The products were normal and iso-aspartyl forms, in both L and D versions.

What drives degradation: form, moisture, heat, oxygen and light

Solution or powder. Bachem says peptides should not be stored in solution, even sterile and oxygen-free, because they slowly degrade. For longer storage it gives the freeze-dried powder in a tightly closed container below −15 °C, with −50 °C or lower preferred, and 4 °C for short-term use. It also says these peptides may be shipped at room temperature.

Moisture. Freeze-dried peptides are hygroscopic. Bachem notes that absorbed water reduces the peptide content and may decrease stability. A 2024 study names temperature, humidity and light as the main stability factors in the solid state. Its authors held insulin powder at 60 °C and 75 % relative humidity. Covalent dimers rose from 6.5 % after one day to 21.1 % after seven, larger oligomers reached 11.1 %, and deamidated insulin made up 10.1 % by day seven.

Heat and oxygen in solution. A Thermo Fisher application note stressed a 1 mg/mL semaglutide solution. After 72 hours at 60 °C the main peak was 4.65 % smaller than in an unheated control, and most new species were shortened chains. A trace of hydrogen peroxide (0.01 %, 14 hours) reduced the main peak by 8.94 %, mainly by adding one or two oxygen atoms to the tryptophan at position 25.

No general rule says how many days a peptide stays unchanged at room temperature; that figure comes from a stability study of one product in one container.

Peptide degradation temperature in stability studies

ICH Q1A(R2) sets the storage conditions for stability studies of medicines:

Label storage	Long-term condition	Accelerated condition
General case	25 °C ± 2 °C and 60 % RH ± 5 %, 12 months	40 °C ± 2 °C and 75 % RH ± 5 %, 6 months
Refrigerator	5 °C ± 3 °C, 12 months	25 °C ± 2 °C and 60 % RH ± 5 %, 6 months
Freezer	−20 °C ± 5 °C, 12 months	None; one batch is held at 5 °C or 25 °C to cover short excursions

The guideline says accelerated data can be used to judge short excursions outside the label storage, such as might occur during shipping. A forced peptide degradation study (stress testing) goes further: 10 °C steps above the accelerated temperature, 75 % RH or more, oxidation, light, and hydrolysis across a range of pH. Its purpose is to find the likely degradation products and to show that the analytical method can see them.

How storage and shipping show up in a result

A test describes the vial as it arrived at the lab. It cannot say when a change happened: at the factory, in a warehouse, in transit or on a shelf.

• A release COA and a later test describe different moments. See factory COAs and outside labs.
• One test can show degradation products, but a change over time shows only against a baseline: an earlier result for the same batch, ideally from the same lab and method. Labs can print different numbers for the same powder; see why labs disagree.
• Send vials sealed; our guide on how to send peptides for testing covers packing.

How to detect peptide degradation with HPLC and LC-MS

HPLC purity. The purity figure is the summary; the impurity peaks are the evidence. Compare the full chromatogram and peak table, peak by peak, with the earlier result. Under the EMA synthetic peptide guideline, peptide-related impurities are reported above 0.1 %, identified above 0.5 % and qualified above 1.0 %, so a method that reports down to 0.1 % can show an early change. Our guide on HPLC peptide purity explains the figure.

LC-MS. Mass spectrometry puts a mass on each new peak: +16 or +32 Da for oxidation, −17 or −18 Da for pyroglutamate, lighter fragments for chain cleavage. Deamidation is harder: its +0.984 Da shift overlaps the isotope peaks of the unchanged peptide, which Dasari and colleagues separated by modelling the isotope pattern.

What both can miss. D-amino-acid and isoaspartate forms have the same mass as the parent peptide; a 2022 study of semaglutide needed chromatographic separation to see them. Some impurities sit under the main peak. In the Thermo Fisher work, a semaglutide chain missing one threonine co-eluted with the main peak at 0.43 % in the unstressed control, above the 0.1 % reporting threshold. The UV trace could not separate it; high-resolution MS found it. It was present before any stress, so not every impurity is degradation.

Peptide aggregation analysis. SEC separates molecules by size: in the insulin study, the high-molecular-weight peak left the column about one minute before the single molecule. Conditions matter: that study’s SEC mobile phase broke up non-covalent clusters, so it counted covalent aggregates only. A Phenomenex note calls SEC the typical method for semaglutide aggregates.

Content and water. If part of the peptide has degraded, the content per vial result falls even when the fill was right. Water content shows moisture uptake.

Degradation inside the lab

Once a lab dissolves a sample, the solution can change while it waits for injection. The Thermo Fisher method held its samples at 4 °C in the autosampler. Finnrick’s method questionnaire asks each partner lab whether it corrects for adsorption or degradation. The published answers:

Lab	Published answer
Krause Analytical (March 2026)	Assumes full recovery; argues that recovery cannot be measured without isotope dilution
Chromate (12 January 2026)	Assumes full recovery; no corrections
BTLabs (8 January 2026)	Assumes full recovery; no corrections
Ichor Life Sciences (1 September 2026)	Full recovery assumed; no correction for adsorption or degradation
PharmLabs (date not shown)	Recovery evaluated during method validation, not assumed

Each is a stated choice. A lab that says what it assumes is easier to compare.

Peptide stability studies and the labs that list them

A single test is a snapshot. Peptide stability testing follows one batch through set time points under set conditions, with the same methods each time. These labs list stability or aggregate work on their own sites, as checked in September 2026:

Lab	What it lists
ACS Peptide Testing Labs	ICH Q1A(R2) studies at 40 °C and 75 % RH with time points to 6 months, and at 25 °C and 60 % RH or 2–8 °C with time points to 36 months; HPLC purity and mass spectrometry for degradation products at each time point; accelerated data in 90 days
MDx BioAnalytical Laboratory	Aggregation profiling; ICH stability testing, including forced degradation and shelf-life estimation
Ethos Analytics	Stability, among its peptide services
Janoshik	GLP-1 aggregate analysis, as an add-on to its GLP-1 test

What HK Analytical does for this question

We test the vial as it arrives, and the report carries our own photo of the vial as received. Purity (HPLC), identity (LC-MS), content per vial, water content (Karl Fischer) and vial-to-vial consistency can go in one order, in any mix per sample. Results within days of receipt. Every number comes with its raw data, so chromatograms from two dates of the same batch can be laid side by side. Aggregate analysis by SEC and formal stability studies are not on our test list. The example report shows the layout, and a quote covers the tests you choose.