Peptide Sequence Impurities: Deletions, Truncations and Insertions Explained
A peptide-related impurity can look very similar to the intended molecule while carrying the wrong sequence. Deletions, truncations and insertions are three important examples.
Synthetic peptide quality is more complicated than asking whether a sample is mostly one chromatographic peak. Because a peptide is assembled as an ordered amino-acid sequence, manufacturing can produce related molecules that resemble the target while containing a sequence difference.
What is a deletion sequence?
A deletion sequence is a peptide in which one or more intended amino-acid residues are missing. The 2026 EMA synthetic-peptide guideline notes that deletion sequences can arise from incomplete reactions during assembly. The resulting molecule may remain close in size and chemical behaviour to the target, which can make analytical separation challenging.
What is a truncated sequence?
A truncated sequence is shorter than the intended full-length peptide because chain assembly stopped before completion. Truncated material may result from process steps used to prevent an incompletely reacted chain from continuing through later stages. The exact impurity pattern depends on the sequence and manufacturing process.
What is an insertion sequence?
Insertion sequences contain one or more additional residues relative to the intended peptide. They can arise when an unintended extra incorporation occurs during assembly. Like deletions, they are sequence-related impurities rather than unrelated process chemicals.
Why HPLC and mass information answer different questions
Chromatography is useful for separating components and estimating the relative abundance of resolved peaks. Mass spectrometry provides information about molecular mass. Neither concept should be reduced to a single universal pass/fail number: co-elution can complicate chromatography, while an expected mass alone does not establish every structural feature or stereochemical detail.
Orthogonal characterization reduces ambiguity
EMA's current peptide guideline emphasizes structural characterization and complementary analytical approaches. The principle is straightforward: confidence increases when methods based on different physical properties support the same identity and impurity interpretation.
Why a COA needs context
A certificate of analysis is most useful when it identifies the analytical method, result, specification and sample or batch to which the data belong. A headline such as '99% purity' without method context cannot explain which sequence-related impurities were detectable, resolved or identified.
Quality-science context only. This article explains analytical concepts and is not a manufacturing protocol.
Related products
See allFrequently asked questions
Can a peptide be 99% pure and still have an identity problem?
A high chromatographic purity result does not by itself prove complete molecular identity. Identity and purity are related but different analytical questions.
What is the difference between a deletion and truncated sequence?
A deletion lacks one or more residues within the intended sequence, while a truncated sequence ends before the intended full length.
Can mass spectrometry replace chromatography?
No. The methods provide complementary information; mass and chromatographic separation answer different questions.
Why are peptide impurities harder than ordinary contaminants?
Sequence-related impurities can be structurally very similar to the target peptide, which may make separation and identification more demanding.
Sources and further reading
About the author
Synedica Research Desk
Scientific content team
The Synedica Research Desk writes and maintains the technical library behind the Synedica Europe catalogue. The team compiles publicly available literature, supplier documentation and analytical data into plain-language explainers for laboratory and research audiences.
- Reviews certificates of analysis supplied with every Synedica batch
- Sources claims from peer-reviewed literature and regulator publications
- Publishes review dates and correction notes on every article
Continue reading
See all
Peptide Purity and HPLC, Explained
Two vials can both claim 99% purity and contain measurably different amounts of peptide. This explains why.
How to Read a Certificate of Analysis
A certificate of analysis is only useful if you can read it. Here is what each section should contain and which omissions should stop an order.
Peptide Mass Spectrometry: What LC-MS Can and Cannot Prove
Mass spectrometry is one of the most useful tools for synthetic peptide identity, but an expected molecular mass is not the same as complete structural proof. Here is how to read LC-MS evidence more accurately.