How to check a chemical certificate of analysis
Compare the certificate with your process specification, not just the supplier's purity headline. Confirm substance identity, assay basis, relevant impurities, suitable methods and results traceable to the delivered lot. Resolve gaps through laboratory checks and a process trial. Ask Cambridge China Bridge to obtain the factory's supporting records.
Start with your process and substance identity
Write down what could disrupt your process: reaction performance, catalyst activity, colour, filtration or finished-product stability. Turn those risks into acceptance criteria before reviewing the certificate. Our chemical sourcing guide covers the wider import and supplier checks; this guide focuses on whether the reported analysis supports your intended use.
Match the chemical name and substance identifier across the order, specification, certificate and container labels. Confirm the required salt, hydrate, stereochemical composition and solid form where relevant. A matching name or identifier alone does not establish that the material has the form your process needs. Ask your laboratory which identity tests can distinguish plausible alternatives.
Find out what the purity result measures
Ask whether the headline result is a calibrated assay or chromatographic peak-area purity. Peak-area purity describes the signals included in that method's calculation; it does not automatically establish the mass fraction of the desired substance. Ask what the detector misses, whether peaks overlap and whether different components have different responses.
Confirm whether the assay is reported as received, on a dried basis or with water and solvents excluded. Ask how corrections are calculated and whether the reported content refers to the complete salt or its active component. Use a basis compatible with your charging calculation, and assess water and solvent results separately where they affect the process.
Check the impurities your process cannot tolerate
Build an impurity list with your technical team using the manufacturing route and downstream risks. Consider residual starting materials, reaction by-products, solvents, water, inorganic residues and metals where relevant. Agree individual limits for critical impurities rather than relying only on total purity. Ask how unidentified peaks are reported and investigated.
For each critical impurity, check whether it was tested, which method was used and how the result is expressed. Distinguish an actual measured result from a specification limit or a statement that the material complies. A result reported as not detected needs its detection limit; it does not establish absence. Ask whether that limit is sensitive enough for your acceptance criterion.
Review methods before comparing results
Obtain the method identifier and revision, sample preparation, reference-standard details, calibration approach and calculation basis. Ask for evidence that the method separates the target from relevant impurities and gives reliable results in this material. Where a result is close to your acceptance limit, ask the laboratory how measurement uncertainty affects the decision.
HSE recommends explaining unexpected findings when the same information appears in different parts of a UK REACH dossier. For your purchasing review, investigate discrepancies between the certificate and independent testing: first compare sampling, preparation, methods and reporting bases. Use the test report verification guide for document checks, and agree how conflicting results will be resolved before ordering.
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Release the delivered lot using its own evidence
Require results for the actual supply lot, with its batch identifier, manufacturing site, sampling and testing dates, specification revision and authorised approval. Match the certificate to container labels and dispatch records. Ask who sampled the material and whether the sample represents the supply lot. The sample chain of custody guide helps preserve that link.
Treat identical results across certificates as a reason to inspect supporting records, rather than proof of copying. Obtain chromatograms, spectra or laboratory worksheets for disputed tests. Hold material with unresolved identity, method or traceability gaps. Release it only after your quality team accepts the evidence and any necessary process trial; keep the decision and retained sample linked to the lot.
Frequently asked questions
Does high purity mean a chemical will work in my process?
No. The wrong form, water content or a critical impurity can still cause problems. Check the assay basis and process-specific limits, then confirm suitability through appropriate testing and a trial.
Is chromatographic purity the same as assay?
Not automatically. Peak-area purity compares included detector signals. A calibrated assay estimates content using a reference standard and stated calculation basis. Ask exactly what the certificate reports.
What if the certificate only says pass?
Request actual batch results for quantitative tests, with units, methods and reporting bases. For qualitative identity tests, request the test outcome and supporting evidence. A specification limit is not a measured result.
What should I do if my laboratory gets a different result?
Hold the lot while checking sample identity, storage, preparation, method revision and calculation basis. Arrange agreed repeat or referee testing using traceable samples, and record the release decision.