What a mineral powder certificate of analysis should state for a shipment — lot number, sampling basis, test methods, specification limits and a statement of conformity — plus the weak points buyers check before accepting one.
Every mineral powder shipment that crosses a border travels with a set of documents, and none of them is read more closely by the buyer's QC team than the certificate of analysis (COA). It is usually one page. It is also the document that decides whether a container is accepted, held or rejected. Yet a COA is only as useful as the information it carries: the same heading can sit above a rigorous, lot-specific test report or above a sheet copied from an old file. This guide sets out what a mineral powder COA should state for a shipment, which parameters matter for each product line, and the weak points worth checking before you accept one.
What a certificate of analysis is — and what it is not
A COA is a declaration by the producer about the material in a defined lot. It records what was measured, on which sample, using which method, and how the result compares with the agreed specification. It is not a marketing data sheet, and it is not the same as an inspection certificate issued by an independent body.
Batch COA versus third-party inspection certificate
A batch COA is issued by the producer for each production lot and travels with the material. A third-party inspection certificate — from a body such as SGS, Intertek or Bureau Veritas — is issued by an organisation independent of the producer, usually against a sample taken at a defined point, for example at loading. The two documents answer different questions: the batch COA tells you what the producer measured and stands behind; the third-party report tells you what an independent laboratory found on the sample it took. Many buyers ask for both on a first order and then rely on the batch COA for repeat shipments. The verification steps behind these documents are covered in our guide to verifying a Chinese mineral powder supplier.
What every shipment COA should state
A COA that can be acted on contains a predictable set of fields. If any of them is missing, ask for a corrected version before the container is released.
- Producer, and the consignee or order reference. The document should be traceable to your order or PO, not to a generic product name.
- Product designation and grade. The name and grade as ordered — for example a talc grade at a stated mesh — so that the COA and the packing list describe the same material.
- Lot or batch number. The single most important field, because it is what ties the results to the material in the container.
- Quantity and packaging. Net weight, number of bags or big bags, and the packing format.
- Date of manufacture, and the date of analysis. A COA written for an earlier lot, or dated well before the material was packed, is a warning sign.
- Sampling basis. How the sample behind the results was taken — a composite sample across the lot, a spot sample, or a retained sample — because the sampling plan decides how representative the figures are.
- Test items with both results and specification limits. A number without a limit tells the buyer nothing about conformity.
- The test method for each result. Sieve analysis and laser diffraction can describe the same powder differently, so the method has to be named.
- A statement of conformity. An explicit sentence confirming that the lot meets the agreed specification, not just a table of figures.
- The issuing laboratory, a signature and a date. Authorisation is what makes the document a certificate rather than a printout.
Which parameters belong on a mineral powder COA
The exact list depends on the product and on your process, but the same three families recur across the range: chemistry, colour and particle size.
Chemistry and colour
For talc powder the chemistry that matters most is the balance of magnesia and silica together with loss on ignition, because these separate a lamellar talc from material diluted with carbonates or chlorite; whiteness and moisture are reported alongside, and for regulated uses the asbestos question is answered by the test method rather than by the wording of a statement. For ground calcium carbonate the central figures are the calcium carbonate content, whiteness and moisture. For dolomite the CaO and MgO content define the double-carbonate character buyers select it for. For magnesia products the reported values centre on MgO content, loss on ignition and, for reactive grades, reactivity. The parameter list should start from your own target tests rather than from the product family, which is why we describe specification values as subject to batch testing rather than as fixed constants.
Particle size, mesh and sieve analysis
Particle size is where COAs most often become hard to compare. Two documents can both say "1250 mesh" and still describe powders with different distributions, because a mesh figure is a single cut point while the distribution describes the whole population of particles. A useful COA reports either a residue on a stated sieve or a full distribution, and names the method. Sieve results and laser diffraction results are not interchangeable, so the method line matters as much as the number. The difference between the two conventions is explained in our mesh size guide and in the article on choosing the right mesh size; the two standards behind those measurements are quoted at the foot of this page.
Sampling, test method and lot traceability
Three things separate a COA you can rely on from one you cannot. The first is sampling: results can only be trusted as far as the sample represents the lot, so a producer that retains and labels samples per lot is in a better position to answer a query months later. The second is method discipline: the same test performed to the same standard gives results you can compare across shipments, while a change of method without a note on the COA can look like a change in quality. The third is traceability, which is simply the ability to connect a container back to a lot number, a production date and a retained sample. How a producer organises sampling, packing checks and retention day to day is covered in our article on quality control in mineral powder production.
Weak points to check before you accept a COA
Most COAs that cause problems are not forged; they are incomplete or applied to the wrong lot. The points below account for a large share of disputes, and each one is quick to check.
- No lot number, or a lot number that does not match the packing list. Without it the figures cannot be tied to the material on the pallet.
- Results with no specification limits. A figure that is not compared with an agreed range cannot show conformity.
- Missing test methods. A particle size figure without a method cannot be compared with your own result.
- Figures that look copied from an earlier shipment. Identical results down to the last decimal, batch after batch, are unlikely for a natural product and suggest the sheet was not reissued for the lot.
- A "typical" value offered in place of a measured one. Typical values belong on a data sheet, not on the certificate for a specific lot.
- A statement of conformity without traceable authorisation. If no laboratory or responsible person is identified, nobody is accountable for the figures.
None of these points requires a laboratory to check. They are read off the document itself, which is why a short review of the COA before release catches most of the risk early.
How TDHX issues a shipment COA
Every TDHX shipment goes out with a batch certificate of analysis and a technical data sheet matched to the grade supplied, and with the lot and packaging details that let the buyer match the document to the container. Sampling runs through production and packing, and samples are retained so that a query about a specific lot can be answered later. Where a buyer needs independent assurance, third-party inspection can be arranged before shipment at the buyer's request. If you would like to see the format we use before ordering, request a sample together with the accompanying documents — the practical questions buyers ask first are collected in our FAQ.
