How to Read a Peptide COA: Field-by-Field Guide | Peptide Intel Hub

A COA is an analytical report produced by a testing laboratory for a specific batch of a specific compound. It records what the laboratory measured — purity, identity, related impurities, water content — and gives the receiving researcher the evidence needed to decide whether the batch meets the project specification.

A credible COA is produced by an independent third-party laboratory (Janoshik Analytical is the industry-standard verifier in Europe), references a specific batch number that matches the vial cap, is dated within the shelf-life window for the compound, and uses analytical methods appropriate to the chemistry of the molecule.

The batch number is the first thing to check: it must match the batch number printed on the vial cap exactly. A COA that references a different batch is not valid for the vial in front of you, even if the compound name matches. The report date matters because most lyophilised peptides have a shelf-life window measured in months from the date of manufacture or release; a COA dated outside that window is a stability flag, not a release certificate.

A verified supplier prints the batch number on the vial cap and on the outer packaging, and publishes the matching COA in its public COA archive within 24 hours of independent release.

The COA must name the compound exactly and state both the theoretical molecular weight (calculated from the sequence) and the measured molecular weight from the mass-spectrometry panel. The two numbers should match within instrument tolerance — typically a fraction of one Dalton for a peptide in the 1–5 kDa range.

If the measured molecular weight does not match the theoretical molecular weight, the batch is not what the label says it is — that is the single most serious COA flag and should always be referred back to the supplier before any reconstitution.

The HPLC chromatogram shows the main peak (the target peptide) and any secondary peaks (related impurities). The main-peak purity is reported as a percentage of total integrated peak area. For research-grade peptides the credible release threshold is ≥98.0%, and a typical verified-supplier minimum specification is ≥99.0%.

A main-peak purity below the specification does not automatically mean the batch is unsafe to use for an in-vitro protocol, but it does mean the secondary peaks should be characterised before the batch is committed to a stability or comparator study — otherwise project conclusions can be contaminated by an unknown impurity contribution.

Related impurities are the secondary peaks on the HPLC chromatogram. For peptide chemistry the common sources are des-amino byproducts (a residue dropped during synthesis), oxidation products (typically methionine or tryptophan oxidation), deamidation products (asparagine or glutamine converted) and incomplete coupling products. A well-characterised batch will identify the major related impurities and report each as a percentage of total peak area.

A clean batch shows a single dominant peak with related impurities in the low-single-digit total. A messier batch shows multiple secondary peaks; that is not always disqualifying, but it changes the experimental risk profile and should be cross-referenced against the project specification.

Lyophilised peptides contain residual water from the freeze-drying process. The water content is measured by Karl Fischer titration or thermogravimetric analysis and reported as a percentage. Most credible lyophilised peptide batches sit between 2% and 8% water content; anything above the published specification is a stability flag because residual water accelerates degradation in the lyophilised state.

A high water-content batch is not automatically unsafe — it just has a shorter realistic stability window and should be reconstituted sooner rather than stored.

The mass-spectrometry panel confirms that the main HPLC peak is in fact the compound named on the label. It does this by measuring the molecular weight of the peak and comparing it to the theoretical molecular weight calculated from the sequence. The two should match within instrument tolerance.

For peptides with modifications (e.g. tesamorelin's trans-3-hexenoyl group, or analogues with fatty-acid side-chains), the mass-spectrometry report should explicitly confirm the modification — not just the base sequence — or the identity confirmation is incomplete.

A credible COA is signed by an identified analyst from an identified laboratory. A COA from an anonymous internal laboratory is not third-party verification; a COA from a named external laboratory with a known address and published methods is. For batches from verified suppliers that signature is from Janoshik Analytical or an orthogonal independent laboratory of equivalent standing.

If the COA does not name the laboratory or the analyst, treat the document as a supplier-internal report and ask for an independent third-party COA before committing the batch to a protocol.

Run this checklist on every batch before reconstitution: (1) batch number on vial = batch number on COA; (2) report dated within the shelf-life window; (3) compound name matches the label; (4) measured molecular weight matches theoretical within tolerance; (5) HPLC main-peak purity meets the project specification; (6) related impurities total within the project tolerance; (7) water content within published specification; (8) COA signed by a named analyst from an identified independent laboratory.

Any single failure is a flag, not a fatal — but all eight passing is the baseline for a confident reconstitution. Once a laboratory has worked through the checklist once, the workflow becomes second nature.

Peptides are an increasingly vital class of pharmaceuticals, situated between classic small organic molecules and larger biomolecules like proteins (PMID 25044089). The peptide drug market is currently expanding at twice the rate of other drug markets, highlighting its significant clinical and economic impact (PMID 25044089). This rapid growth underscores the importance of understanding the quality and verification processes for these complex molecules.

Most peptides today are manufactured using solid-phase peptide synthesis (SPPS) (PMID 25044089). This synthesis method, while efficient, can introduce specific types of impurities. Related impurities and degradants in peptide medicines are critical to control, not only for approved and clinically used peptide drugs but also because they can significantly influence initial functionality studies during early drug discovery, potentially leading to erroneous conclusions (PMID 25044089). Regulatory bodies acknowledge that quality and safety guidelines specific to peptides are limited, necessitating careful consideration of impurities and their toxicological assessment (PMID 39243929).

The characterization of peptide-related impurities cannot follow the same approach as small molecules due to the complex mechanisms of action these larger molecules can exert in the human body (PMID 39243929). Although direct genotoxic mechanisms cannot be ruled out, hazardous interactions on biological systems are a concern, similar to natural peptide toxins and their specific interactions with cellular or membrane targets (PMID 39243929). From a regulatory perspective, a specific safety threshold for potential toxicity should be defined only after specific risk identification and characterization (PMID 39243929).

Peptide impurities can broadly be categorized into those arising from the synthesis process itself and those resulting from degradation mechanisms (PMID 25044089). Solid-phase peptide synthesis (SPPS)-related impurities include deletion and insertion of amino acids, which are linked to inefficient Fmoc-deprotection and excessive use of amino acid reagents, respectively (PMID 25044089). Fmoc-deprotection can also lead to racemization of amino acid residues, forming diastereomeric impurities (PMID 25044089).

Inefficient deprotection of amino acid side chains can result in peptide-protection adducts, and unprotected side chains may react with various reagents used in the synthesis (PMID 25044089). Oxidation of amino acid side chains and the formation of dimeric-to-oligomeric impurities have also been observed (PMID 25044089). Furthermore, unwanted peptide counter ions, such as trifluoroacetate, originating from SPPS or additional purification steps, may be present in the final peptide product (PMID 25044089). Contamination by other unrelated peptides has also been noted, indicating a potential lack of appropriate Good Manufacturing Practices (GMP) (PMID 25044089).

The second group of impurities stems from typical peptide degradation mechanisms. These include β-elimination, diketopiperazine formation, pyroglutamate formation, and succinimide formation (PMID 25044089). These SPPS- and degradation-related impurity types can be found in finished peptide drug products (PMID 25044089). For example, glutathione (GSH), an endogenous tripeptide, can have main related impurities such as L-cysteinylglycine (Impurity A), cysteine (Impurity B), oxidized L-glutathione (Impurity C), and γ-L-glutamyl-L-cysteine (Impurity D), along with a newly identified degradant, L-pyroglutamic acid (pGlu) (PMID 39068812).

To ensure the quality of peptide products, efficient and sensitive analytical methods are crucial for assessing impurities (PMID 39068812). Liquid chromatography-high resolution mass spectrometry (LC-HRMS) is a promising approach for peptide quality control, including the measurement of peptide-related impurities (PMID 25716148). This method can detect impurities present at less than 0.1% of the drug product's active pharmaceutical ingredient (API) concentration (PMID 25716148). LC-HRMS offers added benefits such as the ability to determine amino acid composition, confirm peptide sequence, and quantify co-eluting impurities within a single experiment (PMID 25716148).

Other chromatographic methods are also vital. High-performance liquid chromatography (HPLC) with UV detection is widely used. For instance, an isocratic HPLC-UV procedure was developed and validated for glutathione, separating and identifying GSH and its related impurities (A-D) and L-pyroglutamic acid (pGlu) within 10 minutes (PMID 39068812). This optimized HPLC method for GSH assay does not suffer interference from impurities A, B, and D, providing highly specific results compared to the commonly used iodine titration method (PMID 39068812). Similarly, a novel HPLC method has been developed and validated for atosiban and its five related substances in atosiban acetate injection, offering specific and reproducible determination (PMID 31585328). This method also combines mass spectrometry to characterize the molecular weight and tentative structure of impurities (PMID 31585328).

Ultrahigh performance liquid chromatography quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF-MS) has been used to investigate the impurity profile of norvancomycin hydrochloride, characterizing thirteen impurities and two degradation products (PMID 42571917). Micellar electrokinetic capillary chromatography (MEKC) is another technique, developed for the analysis of goserelin and related substances, offering advantages over RP-HPLC by better resolving overlapping impurity signals and providing shorter migration times (PMID 26635325). For complex biotherapeutics, a novel strategy integrating data-dependent acquisition (DDA), parallel reaction monitoring (PRM), and multiple reaction monitoring (MRM) techniques can comprehensively profile and accurately quantify high-risk host cell proteins (HCPs), which are critical process-related impurities (PMID 40562700).

The quality of drugs directly impacts patient safety (PMID 42571917). Despite this, studies have shown discrepancies between stated purity levels on supplier certificates of analysis (CoAs) and in-house quality control (QC) results for peptides used in research and development (PMID 29403929). In one evaluation of quorum sensing peptides, only 44.0% met the required purity of at least 95.0% according to in-house QC, even finding that the main compound of one sample had a different structure than desired (PMID 29403929). This highlights that relying solely on supplier-provided CoAs can have serious consequences for peptide research, emphasizing the need for researchers to implement and maintain thorough in-house QC (PMID 29403929).

The presence of impurities in peptide products is a significant concern. Several incidents of toxicity have occurred due to endotoxin or otherwise contaminated glutathione (GSH) in compounded drugs, underscoring the need for rigorous quality assessment (PMID 39068812). A study on oxytocin and tranexamic acid, used for postpartum hemorrhage, found that only six out of 17 unique oxytocin products had adequate content and no related substances exceeding recommended limits (PMID 35762808). Furthermore, while most tranexamic acid samples had adequate content, the presence of impurities in multiple products was deemed worrying and warranted further study (PMID 35762808).

An interesting degradation phenomenon was reported where glucagon from a specific vendor underwent rapid cleavage of several peptide bonds under near neutral to basic conditions, attributed to contamination by a thermostable high molecular impurity, possibly a peptidase (PMID 31161359). This case demonstrates that products meeting rudimentary quality standards might still contain impurities that cause significant degradation (PMID 31161359). A suggested solution is for manufacturers to perform additional stability tests under real or accelerated conditions and include 'accelerated stability criteria' in CoAs, especially for sensitive biological reagents prone to faster degradation (PMID 31161359).

For therapeutic peptides, especially biosimilars, a comprehensive evaluation extends beyond basic purity to include analytical similarity. Biosimilars offer safe and effective treatment options, aiming for equivalent safety, efficacy, and quality compared to innovator products (PMID 41033058). This requires extensive physicochemical, structural, and functional characterization to support biosimilarity development (PMID 41033058). For example, an analytical comparison of BVZ-BC (bevacizumab-biosimilar candidate) and bevacizumab involved state-of-the-art analytical techniques to evaluate multiple attributes, including amino acid sequence, disulfide structure, glycan profiles, free thiol content, isoelectric point, protein content, subvisible particles, higher-order structure, product purity, and product-related and process-related impurities (PMID 31983199).

Biological activity assessment is also critical for biosimilarity. This involves orthogonal assays like cell-based bioassays and enzyme-linked immunosorbent assays (ELISA) to interrogate all expected biological activities (PMID 31983199). In the comparison of BVZ-BC and bevacizumab, an accumulation of 18 batches of bevacizumab and 10 batches of BVZ-BC were utilized to assess and demonstrate the similarity of all quality attributes (PMID 31983199). An orthogonal biosimilarity protocol for etanercept, a fusion protein, also employed methods like peptide mapping-reverse phase HPLC, size exclusion HPLC, dynamic light scattering, SDS-PAGE, direct UV spectrophotometry, and ELISA to assess content and protein binding activity (PMID 41033058).

Consistency across batches is a hallmark of quality. When optimizing pharmaceutical manufacturing, approaches like Quality by Design (QbD) are recommended to develop robust drug manufacturing and control methods (PMID 34219919). This includes identifying critical parameters for achieving stable formulations, as demonstrated in the preparation of alpha-galactosidase-loaded nanoliposomes (nanoGLA) for Fabry disease (PMID 34219919). Mass balance analysis, while useful for characterizing analytical methods and understanding manufacturing processes, should not be a required specification control but rather demonstrated during method development and forced degradation experiments, as it can create non-value-added investigations if used as an acceptance criterion (PMID 39442464).

The presence of impurities in peptide products can have significant biological implications. Peptide-related impurities, encompassing both active pharmaceutical ingredients (API) and finished drug products, can greatly influence initial functionality studies during early drug discovery phases, potentially leading to erroneous conclusions (PMID 25044089). Regulatory bodies emphasize that the characterization of these impurities must consider their complex mechanisms of action in the human body, as hazardous interactions on biological systems cannot be ruled out (PMID 39243929).

In some cases, impurities can directly lead to toxicity. Incidents of toxicity have occurred in recent years due to endotoxin or otherwise contaminated glutathione in compounded drugs (PMID 39068812). Beyond direct toxicity, impurities can affect drug stability and safety. Host cell proteins (HCPs) are critical process-related impurities in biotherapeutics that pose a threat to drug stability and safety (PMID 40562700). Understanding and quantifying these high-risk HCPs is essential for biopharmaceutical process development (PMID 40562700).

The immune response to therapeutic proteins, including peptides, is a major risk. The generation of anti-drug antibodies (ADAs) can lead to the formation of immune complexes (ICs), which consist of the drug and ADAs (PMID 34763611). These ICs can impact safety, efficacy, and exposure (PMID 34763611). Studies have shown that increasing immune complex size leads to increased clearance of the drug, and complexes formed with a wildtype Fc domain showed faster clearance compared to immune effector function modified drugs (PMID 34763611). This indicates that drug clearance due to ADA generation is influenced by the size and structure of formed ICs, as well as the immune effector functions of the Fc domains of IgGs (PMID 34763611).

Long-term stability and robust control strategies are essential for peptide therapeutics. A validated, stability-indicating HPLC method has been developed for the simultaneous determination of five related substances in liraglutide drug substance, an analog of glucagon-like peptide-1 used for type 2 diabetes mellitus and obesity (PMID 40442972). This method ensures quality control of liraglutide products by efficiently separating and quantifying both the main compound and its impurities (PMID 40442972). The method was validated according to International Conference on Harmonization (ICH) guidelines for specificity, linearity, limit of detection, limit of quantification, accuracy, precision, and robustness (PMID 40442972).

Stress degradation experiments are integral to ensuring the specificity of analytical methods and understanding potential degradation pathways (PMID 42571917). The concept of mass balance, while not always suitable as a formal quality acceptance criterion due to potential for non-value-added investigations, is valuable for characterizing the performance of analytical methods and for a rigorous understanding of the manufacturing process and control strategy development (PMID 39442464). It should be demonstrated during method development and through well-designed forced degradation experiments (PMID 39442464).

The presence of impurities can also have consequences for preclinical and clinical studies. For instance, in a mouse model studying the impact of chemotherapy on reproductive function, changes in sperm quality, testicular weight, and inflammatory markers were observed (PMID 39533240). While this specific study is not about peptide impurities, it illustrates how subtle changes can have significant biological impact, reinforcing the need for rigorous quality control in all pharmaceutical products. Similarly, preclinical animal models for pulmonary fibrosis induction utilize carefully controlled doses of agents like bleomycin, where the optimal dosage was determined to be 3 mg/kg in mice to induce fibrosis with minimal animal distress, demonstrating the careful consideration of compound effects in research (PMID 41286912).

• Related impurities in peptide medicines. — Journal of pharmaceutical and biomedical analysis (2014). PMID 25044089
• Aspects of complexity in quality and safety assessment of peptide therapeutics and peptide-related impurities. A regulatory perspective. — Regulatory toxicology and pharmacology : RTP (2024). PMID 39243929
• Liquid Chromatography-High Resolution Mass Spectrometry for Peptide Drug Quality Control. — The AAPS journal (2015). PMID 25716148
• An isocratic HPLC-UV analytical procedure for assessment of glutathione and its related substances. — Journal of pharmaceutical and biomedical analysis (2024). PMID 39068812
• Analytical Similarity of a Proposed Biosimilar BVZ-BC to Bevacizumab. — Analytical chemistry (2020). PMID 31983199
• Identification of Impurities in Norvancomycin Hydrochloride Drug Substance Using UHPLC-QTOF-MS. — Rapid communications in mass spectrometry : RCM (2026). PMID 42571917
• Mass balance analysis for therapeutic peptides: Case studies, applications, and perspectives. — Journal of pharmaceutical and biomedical analysis (2025). PMID 39442464
• A Validated, Stability-Indicating HPLC Method for the Simultaneous Determination of Five Related Substances in Liraglutide Drug Substance. — Biomedical chromatography : BMC (2025). PMID 40442972
• Quality of oxytocin and tranexamic acid for the prevention and treatment of postpartum hemorrhage in Kenya, Nigeria, South Africa, and Tanzania. — International journal of gynaecology and obstetrics: the official organ of the International Federation of Gynaecology and Obstetrics (2022). PMID 35762808
• A Novel Strategy to Rapidly Profile and Quantify High-Risk Host Cell Proteins Using Integrated DDA-PRM-dMRM Mode. — Journal of proteome research (2025). PMID 40562700
• Development and validation of a micellar electrokinetic capillary chromatography method for the determination of goserelin and related substances. — Electrophoresis (2016). PMID 26635325
• A novel HPLC method for analysis of atosiban and its five related substances in atosiban acetate injection. — Journal of pharmaceutical and biomedical analysis (2020). PMID 31585328
• The impact of immunogenicity on therapeutic antibody pharmacokinetics: A preclinical evaluation of the effect of immune complex formation and antibody effector function on clearance. — mAbs (2021). PMID 34763611
• Application of Quality by Design to the robust preparation of a liposomal GLA formulation by DELOS-susp method. — The Journal of supercritical fluids (2021). PMID 34219919
• Optimization of intranasal bleomycin dose for effective pulmonary fibrosis induction in mice with minimal animal distress. — BMC pulmonary medicine (2025). PMID 41286912
• Quality evaluation of synthetic quorum sensing peptides used in R&D. — Journal of pharmaceutical analysis (2015). PMID 29403929
• Prediction model of male reproductive function damage caused by CHOP chemotherapy regimen for non-Hodgkin's lymphoma. — BMC cancer (2024). PMID 39533240
• Uncommon Peptide Bond Cleavage of Glucagon from a Specific Vendor under near Neutral to Basic Conditions. — Pharmaceutical research (2019). PMID 31161359
• Orthogonal biosimilarity testing of etanercept: A green and white analytical approach. — Talanta (2026). PMID 41033058