How to Read a Certificate of Analysis

What is a Certificate of Analysis?

A Certificate of Analysis, commonly abbreviated to COA, is a document summarising analytical results for a stated material or batch.

A useful COA should identify:

• what was tested;
• which batch or sample was tested;
• which methods were used;
• which specifications applied;
• what results were obtained;
• whether the material met those specifications;
• who issued or authorised the document.

A COA is a summary document. It is not necessarily the complete analytical data package.

Supporting material may include:

• chromatograms;
• mass spectra;
• sequence data;
• calculations;
• instrument reports;
• sample-receipt records;
• laboratory worksheets;
• method-validation information;
• chain-of-custody records.

Start with traceability

Before reviewing a purity value, confirm that the document can be traced to the material being assessed.

Check:

A high reported purity cannot compensate for a missing or mismatched batch identifier.

Read specifications and results separately

A specification is the predefined acceptance requirement.

A result is the value obtained during testing.

For example:

• Specification: purity not less than 98.0%
• Result: 99.1%
• Conclusion: passes

The COA should make it clear which number is the acceptance criterion and which number is the measured result.

Watch for vague entries such as:

• “complies” without stating the underlying specification;
• “high purity” without a numerical result;
• “passed” without identifying the test method;
• “99%” without stating what was measured.

Identity, purity and assay are not interchangeable

Identity

Identity testing evaluates whether the sample is consistent with the intended compound.

Possible techniques include:

• mass spectrometry;
• LC-MS;
• peptide mapping;
• relative retention time;
• amino-acid analysis;
• nuclear magnetic resonance.

The EMA recommends using suitable orthogonal methods to confirm peptide identity rather than relying on one signal alone.^[1]

Purity

Purity testing often uses a chromatographic method such as reversed-phase HPLC.

The result commonly describes the relative proportion of detected chromatographic peak area attributed to the main peak under that method.

It does not independently establish the exact amount of peptide in the container.

Assay or content

Assay addresses the amount of the specified substance, usually using a reference standard and a defined calculation.

For peptide materials, the calculation basis matters. Water, residual solvents and counter-ions may affect the difference between total powder mass and peptide-base content.

Examine the method information

A strong COA or supporting report should identify the analytical procedure sufficiently clearly.

For HPLC this may include:

• method or procedure number;
• column type;
• detector wavelength or detector type;
• mobile phases;
• gradient;
• flow rate;
• injection volume;
• run time;
• system-suitability criteria;
• integration approach.

For mass spectrometry this may include:

• instrument or technique;
• ionisation mode;
• theoretical mass;
• observed mass;
• mass tolerance;
• relevant interpretation.

A result without enough method context can be difficult to evaluate or reproduce.

Look for raw-data support

Where appropriate, check whether the report is supported by:

• a full chromatogram;
• clear axis labels;
• sample identification;
• acquisition date;
• peak table;
• retention times;
• integrated peak areas;
• system-suitability information;
• mass spectrum;
• theoretical and observed mass values.

A cropped image containing only one peak and a percentage provides less evidence than a traceable analytical report.

Understand the laboratory's accreditation scope

ISO/IEC 17025 accreditation assesses laboratory competence, impartiality and consistent operation.

However, accreditation applies to a defined scope. A laboratory being accredited for one type of test does not automatically mean that every test it offers falls within its accredited scope.

Where accreditation is claimed:

1. identify the accreditation body;
2. verify the laboratory;
3. inspect the current accreditation schedule;
4. confirm whether the specific method or testing field is included;
5. check that the accreditation was valid when the test was performed.

UKAS explains that ISO/IEC 17025 accreditation considers areas including staff competence, method suitability, equipment, environment, sample handling and quality assurance.^[2]

Do not describe a laboratory report as “UKAS accredited” unless the relevant activity is genuinely covered by its current UKAS scope.

Understand the sampling limitation

A third-party laboratory ordinarily reports on the sample it received.

The result does not automatically prove that every vial in a larger batch is identical unless the sampling and batch-control process supports that conclusion.

Important questions include:

• Who selected the sample?
• Was it taken from the finished batch?
• Was the container sealed?
• Was chain of custody documented?
• Does the laboratory sample number link to the supplier batch number?
• Was the tested material representative of the released stock?

Common warning signs

Treat the following as reasons for further verification:

• no batch or lot number;
• batch number does not match the product;
• no laboratory contact information;
• no unique report identifier;
• no testing date;
• no analytical method;
• purity shown without a chromatogram;
• mass identity claimed without observed mass data;
• generic “99% purity” wording;
• cropped or low-resolution reports;
• unexplained editing;
• inconsistent product names;
• duplicated reports across different batches;
• unverifiable accreditation claims;
• no authorised sign-off;
• report supplied only as an editable document;
• acceptance criteria added after results are known.