Assay & Certificate of Analysis: What Metals & Minerals Buyers Should Check

In metals and minerals trade, the value of a shipment depends on what it actually contains — the metal content, the grade, and the impurities. An assay is the chemical analysis that measures this, and the Certificate of Analysis (COA) is the document that records the result. For a wholesale buyer, the assay is often more important than any description, because two lots with the same name can be worth very different amounts.

What an assay measures

An assay reports the composition of a material: the percentage of the primary metal or mineral (for example P₂O₅ in phosphate rock, Fe in iron ore, or Cu in a copper concentrate), together with moisture, particle size where relevant, and the impurities or penalty elements that reduce value or cause processing problems. Pricing for many commodities is tied to this analysis, so the assay directly affects the settled amount.

Why the source of the assay matters

A certificate is only as reliable as the party that produced it and the sample it was taken from. A document with a convincing letterhead does not prove that the sample relates to the lot you are buying. The strongest protection is an assay performed by an internationally accredited, buyer-appointed inspector — firms such as SGS or Bureau Veritas — on a properly drawn, sealed sample, with the sampling method and chain of custody agreed in writing beforehand.

Agree the process before you pay

Settle sampling, lot identification, who appoints and pays the inspector, and the rules for resolving a dispute, before any funds move. Resistance to an independent, pre-payment assay is a reason to slow down and verify, not a detail to overlook. Confirm certificates directly with the issuing body through a channel you source yourself, rather than one the counterparty provides.

Keep the records

Retain the sampling report, the COA, and any correspondence that defines the agreed specification. These are the evidence you will rely on if the delivered material does not match. On Sentrick Metals & Minerals, a lab assay is a first-class document type in supplier qualification and in quotes, so the analysis travels with the trade rather than being left to memory.

Start sourcing with clear specifications

Sentrick Metals & Minerals is a qualified B2B wholesale marketplace for metals, minerals and related materials. See how buyers request quotes with the grade, purity and documents they need.