Quality documents, and what they actually prove
A certificate of analysis is only worth what its test methods are worth. This page sets out what each document should contain, which figures matter commercially, and where phosphate shipments most often end up in dispute.
The certificate of analysis
The COA is issued for a specific production lot by the producer, and it is the document that governs acceptance. Four things make it usable rather than decorative.
- It identifies the lot. A COA without a lot or batch number cannot be tied to the material in the bag, and a surveyor will say so.
- It states the test method for each figure. "P2O5 46%" means little; "P2O5 46.2% by citrate-soluble extraction" can be checked.
- It distinguishes available from water-soluble P2O5. These are different numbers and phosphate disputes usually start where the distinction was left out.
- It is issued by the plant, not by the trader. A trader-issued analysis that does not come from the production site is worth nothing at the port, and in a letter of credit it is worse than nothing.
The figures that decide acceptance
| Parameter | Why it matters |
|---|---|
| Total and available P2O5 | The headline figure, and the one the price is built on |
| Water-soluble P2O5 | Decides immediate availability; critical for soluble and fertigation grades |
| Moisture | Drives caking, and it is weight you paid for that is not nutrient |
| Granule size distribution | Decides whether the material can be blended without segregating |
| Crushing strength | Decides how much fines are produced by handling and spreading |
| Free acid | Corrodes equipment and bag liners; particularly relevant for superphosphates |
| Water-insoluble residue | The figure that decides whether a grade is genuinely fertigation quality |
The technical data sheet
The TDS describes the product rather than the lot: typical analysis, physical properties, solubility, storage and handling, and recommended application. It is what you send to a customer who is evaluating the product, and what a registration dossier is usually built from.
The material safety data sheet
The MSDS covers transport classification, handling precautions, first aid and disposal. For solid phosphate fertilizers it is short, because the material is not classified as dangerous goods. For phosphoric acid it is not short: UN 1805, Class 8, corrosive, with the packaging and carrier requirements that follow from that classification.
Third-party inspection
An independent surveyor — SGS, Intertek, Bureau Veritas or a named local firm — samples and analyses at loading, and issues a certificate that stands apart from the producer's own COA. It is worth the cost when the cargo is large, when the destination authority samples on arrival, or when the specification has been disputed before. The scope has to be agreed in advance: which parameter, which method, and at which point in the loading.
Where disputes actually come from
Almost never from a product that failed. Almost always from a contract that did not say which number was being promised. Three failures account for most of it: a P2O5 figure quoted on a different basis from the one the buyer tests; a granule size tolerance left unstated; and a moisture limit omitted because it seemed obvious.
The guaranteed analysis is issued per production lot and confirmed against the TDS and COA supplied with the quotation.
Documents are issued on a per-shipment basis. Certification availability is confirmed for each order before contract.
Send us the specification you have to meet
A tender document, an existing supplier's COA, or a registration dossier — send it and we will confirm line by line what the material can and cannot meet.