Reference
A Certificate of Analysis, explained for the person who checks it
What a CoA contains, how its limits are written, what the supplier is and is not vouching for, and where a mistake tends to hide when a lot is waiting to be released.
This page is general background. Your quality system and your specifications decide what is checked and by whom.
What is a Certificate of Analysis?
- Certificate of Analysis (CoA)
- A Certificate of Analysis is a document issued by a manufacturer or a laboratory that states, for one batch or lot of a product, the tests performed, the result of each, and the specification each result is measured against. It identifies the product, the lot, the relevant dates and who issued it.
A CoA is the supplier's statement about a lot. It is one input to an acceptance decision: your quality system decides what else is done on receipt, for example identity testing or your own analysis, and who signs off.
A lot-specific CoA lists results for that lot. A sheet of typical values or a generic specification sheet is not a CoA for the lot, however similar it looks.
How to read a CoA, top to bottom
The order that catches most problems early.
Match the identity block
Product name, grade, product code and lot or batch number must match the purchase order and the container labels. A lot number that differs by one character is a different lot.
Check the dates
Manufacture date, expiry or retest date and sampling date should be in a sensible order, and the remaining shelf life should suit your use. A retest date is not an expiry date.
Read the specification, not only the result
Note the limit that applies, its unit and its basis (as is, dried, anhydrous). A result is only meaningful against the limit printed beside it.
Compare each result with its limit
Mind inclusive and exclusive limits, unit differences, and results written as less-than values or as not detected.
Look at the methods
Compendial (USP, Ph. Eur.) or in-house, and whether they match the methods of earlier lots. A changed method can explain a changed result.
Check who issued it and whether it is complete
A named issuer or approver, and every test that your specification requires. A missing test is a gap, not a pass.
Record the outcome
Log the lot, the dates and what the comparison showed, then pass the decision to the person who owns it.
How limits are written on a CoA
- NMT or ≤ or max: not more than. The limit is included, so a result equal to it passes.
- NLT or ≥ or min: not less than. Also inclusive.
- < and >: strictly below or above. < 10 cfu/g means 10 cfu/g does not meet the limit.
- A range, such as 98.0 – 102.0 %, 95.0 to 105.0 or 100 ± 5: both ends are included.
- On the dried basis, as is, anhydrous: the basis of the calculation. It changes the number, so it matters when comparing lots or suppliers.
- Negative, Absent in 25 g, Not detected: a requirement that the thing must not be found, usually for microbial tests.
- Conforms, Complies: a statement against a descriptive or compendial requirement, for example an identification test.
- Report, For information: a value is recorded but no limit applies.
- ND, < LOQ, < 0.01: below what the method can detect or quantify. They are only meaningful if the detection value is not larger than the limit.
Where mistakes hide
- Units: a result in mg/kg against a limit in ppm is fine, but ppm against % is a factor of 10,000.
- Decimal commas: 0,5 is 0.5 in many countries, and 1,000 can be one or one thousand.
- A '<' result that is larger than the limit: < 0.01 % cannot prove compliance with NMT 0.005 %.
- A statement instead of a value: Complies next to a numeric limit gives you nothing to verify.
- A certificate for another lot: lot number, dates and results copied from an earlier certificate.
- A missing test: the certificate omits a parameter that your specification requires. A reader of the certificate alone cannot see this; compare the list of tests with your own specification.
- The supplier's own Pass column disagreeing with the numbers beside it.
Checking a CoA: by eye, from a PDF copy, or with CertiClean
What each approach can and cannot catch.
| What you need | Manual spec check | Generic PDF-to-Excel | CertiClean |
|---|---|---|---|
| Identity block and dates | Read and matched against the order and labels. | Copied into cells. | Read into labelled header fields. You still match them to the order and labels. |
| Result against limit | Compared row by row. | Not compared. | Compared by rule on every row, with a reason. |
| Units and basis | Checked if you notice. | Not checked. | % ↔ ppm ↔ mg/kg converted; other unit mismatches flagged. The basis (dried, as is) is shown in the printed text, not interpreted. |
| A missing test | Caught if you compare with your specification. | Not caught. | Not caught: only printed rows are seen. Compare the list with your own specification. |
| Is the certificate genuine | Your procedures and supplier knowledge. | Not addressed. | Not addressed. |
| Recording | Typed into a log. | A separate sheet per file. | A line in a browser log, with the decision columns left to you. |
CertiClean reads what is printed. It does not know what should have been printed.
Questions people ask
What is a Certificate of Analysis?
A document from a manufacturer or laboratory giving, for one lot of a product, the tests performed, the result of each and the specification it is measured against, with the product, lot, dates and issuer. It is the supplier's statement about that lot.
What is the difference between a CoA and a Certificate of Conformance?
A CoA reports test results for a lot. A certificate of conformance states that the product meets stated requirements and usually gives no results. A conformance statement alone gives you nothing to compare with the limits.
What do NMT and NLT mean?
Not more than and not less than. NMT 0.5 % is a maximum of 0.5 %, and NLT 98.0 % is a minimum of 98.0 %. Both include the stated value, so a result equal to the limit passes.
What does 'on the dried basis' mean?
The result is calculated as if the material contained no loss-on-drying components such as water. The same material gives a higher assay on the dried basis than as is, so compare like with like.
What is the difference between a retest date and an expiry date?
An expiry date is the date after which the material should not be used. A retest date is the date by which it should be tested again to confirm it still meets specification, after which it may be used if it does. Do not treat one as the other.
Does a CoA replace testing on receipt?
Not by itself. What you test on receipt, for example identity, depends on your quality system and the material. The certificate is one input to that decision.
What do ND, BLQ and < LOQ mean on a CoA?
Not detected, below the limit of quantification, and less than the limit of quantification. The value is below what the method can report. It supports a maximum limit only if the detection or quantification value is not larger than that limit.
What should make me suspicious of a CoA?
A lot number or dates that do not match the order, results identical to an earlier lot, Complies printed against numeric limits, a Pass column that disagrees with the numbers, methods that changed without notice, or tests missing from the list.
Can CertiClean tell me whether a certificate is genuine?
No. It reads what is printed and compares it with the printed limits. It does not authenticate a document or check the supplier's laboratory data.
Can it tell me that a required test is missing?
No. It sees only the rows on the certificate and does not know your specification. Compare the list of tests with your own specification.