Peptide Deamidation in 2026: How a Tiny Chemical Change Can Alter Peptide Identity, HPLC & Mass-Spectrometry Results

Peptide quality is not static. Even when a peptide has been synthesised correctly, subtle chemical changes can occur during purification, analysis or storage. One of the most important is deamidation — a modification that can affect asparagine, glutamine and terminal amide groups.

A 2026 research paper from the Laboratory of Pharmaceutical Analytics at ETH Zurich provides a particularly useful look at this problem. The researchers investigated deamidation and isoaspartate formation under routine laboratory conditions and tested whether tandem mass spectrometry could distinguish modifications that conventional chromatography and precursor-mass measurements may struggle to resolve.

What is peptide deamidation?

Deamidation converts an amide functionality into a carboxylic acid. In peptides, this can occur at susceptible asparagine or glutamine side chains and at an amidated C-terminus. Although the chemical change is small, it can alter charge and molecular properties.

For asparagine, deamidation can also proceed through a cyclic succinimide intermediate. Hydrolysis of that intermediate may produce ordinary aspartate or isoaspartate (isoAsp). IsoAsp is especially interesting analytically because it changes the peptide backbone connectivity while remaining isobaric with Asp.

Why can deamidation be difficult to detect?

The ETH Zurich study highlights an analytical problem: deamidation produces a mass increase of approximately 0.984 Da. That lies very close to the peptide’s natural M+1 isotopic peak, so adequate mass resolution and careful interpretation are required.

A second challenge is that Asp and isoAsp have the same nominal molecular composition. Measuring the intact precursor mass therefore cannot, by itself, tell researchers which structure is present. Reversed-phase liquid chromatography may provide only small retention differences, and modified species can partially co-elute.

What the 2026 study investigated

Erckes and colleagues used peptide models containing susceptible amide groups and examined how common analytical, purification and storage environments affected them. They then evaluated two tandem mass-spectrometry fragmentation approaches: collision-induced dissociation (CID) and electron-transfer dissociation (ETD).

Both methods could provide information that was unavailable from precursor mass alone. CID fragmentation helped localise approximately +1 Da changes to particular positions, while ETD produced diagnostic fragments that could distinguish isoAsp in the experimental system. The authors also developed a semi-quantitative workflow for monitoring these changes even when chromatographic separation was incomplete.

Read the 2026 RSC Medicinal Chemistry research article.

pH changed the degradation pathway

One of the most useful findings was that different chemical environments did not simply change the speed of degradation — they could favour different pathways.

Under near-neutral phosphate-buffered conditions in the model system, the researchers observed time-dependent isoAsp formation consistent with a succinimide-mediated pathway. Under acidic aqueous conditions, direct hydrolysis was more prominent and isoAsp was not detected in the same way.

This illustrates why the phrase “peptide degradation” can be too broad on its own. Two samples may both be changing, but the molecular products and mechanisms involved can differ substantially.

What did the study find about TFA?

Trifluoroacetic acid (TFA) is widely encountered in peptide purification workflows. In the study, aqueous acidic conditions containing TFA promoted deamidation in the model peptides, with the extent depending on factors including TFA concentration and water content.

The researchers found that low-percentage aqueous TFA accelerated deamidation, whereas nearly anhydrous TFA produced little or no conversion under the conditions examined. This is an important reminder that the presence of a reagent alone does not determine stability: concentration, water activity, temperature, sequence and exposure time all matter.

Temperature made a major difference

In the acid-driven experiments, degradation increased with temperature. The researchers reported pronounced degradation at 60°C, slower change at 20°C and negligible change at 4°C and −20°C over the study period, including the freeze-thaw conditions they tested.

These findings should not be converted into a universal storage rule for every peptide. Stability is sequence- and formulation-dependent. What the experiment demonstrates is the value of defining storage conditions when assessing peptide stability rather than assuming that a purity result obtained at one point remains unchanged indefinitely.

Not every amide site behaved the same way

The study extended its analysis beyond a single modification site. Asparagine, glutamine and C-terminal amides did not all show identical susceptibility. In the sequences tested, C-terminal amides were particularly susceptible under some acidic conditions.

That site dependence is important. Deamidation risk cannot be predicted from the simple fact that a peptide contains an amide group. Local sequence, molecular structure and experimental conditions influence the pathway and rate.

CID versus ETD mass spectrometry

Tandem mass spectrometry works by fragmenting selected peptide ions and examining the resulting fragments. Different fragmentation techniques can reveal different structural information.

Collision-induced dissociation (CID)

CID commonly produces b- and y-type fragment ions. These fragments can help researchers locate a deamidation-associated mass change within a peptide sequence. However, distinguishing Asp from isoAsp using CID alone can be difficult and sequence-dependent.

Electron-transfer dissociation (ETD)

ETD produces a different fragmentation pattern, principally c- and z-type ions. In the ETH Zurich work, diagnostic ETD fragments helped identify isoAsp and supported semi-quantitative assessment. This illustrates why complementary analytical approaches can be more informative than relying on one measurement.

HPLC purity is not the whole story

HPLC remains a fundamental analytical technique for peptide research, but a chromatogram must be interpreted within the capabilities of the method. Closely related species may have similar retention behaviour, and partial co-elution can obscure structural differences.

Likewise, intact-mass measurement is extremely useful for confirming molecular mass, but isobaric structures cannot always be differentiated by precursor mass alone. The 2026 research therefore supports a broader principle: analytical confidence comes from matching the method to the question.

If the question is “what percentage of UV-detectable material appears in the principal chromatographic peak?”, HPLC may address it. If the question is “has an isoAsp backbone rearrangement occurred?”, additional structural information may be needed.

How deamidation differs from aggregation

Our recent article on peptide aggregation looked at molecules associating into oligomers and larger assemblies. Deamidation is fundamentally different: it is a chemical modification of the peptide molecule.

The distinction is useful when thinking about stability:

• Aggregation concerns physical association between molecules.
• Deamidation changes an amide functionality and may alter charge or backbone connectivity.
• Oxidation, hydrolysis and other degradation reactions represent additional chemical pathways.

A complete stability investigation may therefore need to consider both chemical and physical changes rather than treating “purity” as a single universal measurement.

What does this mean for peptide quality research?

The new research reinforces several principles relevant to analytical peptide work. Sample history matters. Purification solvents, pH, temperature and time can influence what is eventually measured. Small modifications can be analytically challenging, and apparently similar species may require tandem or orthogonal techniques to distinguish them.

It also reinforces the importance of understanding what a Certificate of Analysis actually demonstrates. A COA should be interpreted according to the analytical methods used and the questions those methods are capable of answering.

Key takeaways

• Deamidation is a chemical modification that can affect Asn, Gln and terminal amide groups.
• Asn deamidation may also produce isoAsp through a succinimide-mediated pathway.
• The approximately +0.984 Da change can be challenging to distinguish from isotopic signals without sufficient analytical resolution.
• Asp and isoAsp are isobaric, meaning intact precursor mass alone cannot reliably distinguish them.
• The 2026 ETH Zurich study demonstrated complementary roles for CID and ETD tandem mass spectrometry.
• pH, temperature, solvent environment, sequence and exposure time can influence degradation behaviour.
• HPLC purity, molecular identity and structural integrity are related but separate analytical concepts.

Further 24hour Peptides research

Continue with our articles on peptide degradation and HPLC/MS, peptide aggregation, peptide stability and lyophilisation, peptide preservation and the COA Library.