Certificat d'analyse et assay : comment lire les chiffres

Certificate versus specification

A specification sheet says what a seller promises or a buyer requires, usually as a range or a limit. A certificate of analysis, or assay certificate, says what a laboratory found in a sample. Comparing the two line by line is the core of quality control in commodity trade.

Read the header first

• Issuer: the laboratory or inspection company, with address and any accreditation it states.
• Sample identification, lot or shipment reference and the dates of sampling and analysis.
• Where and how the sample was taken, and how many increments it represents.
• Test methods or standards used for each value.
• Whether the sample was drawn by an independent party or by the seller.

What the numbers mean

Basis and units

Percentages can be by weight on a dry or as-received basis. Ranges can be minimum, maximum or typical. Know which one you are reading. A typical value is a description, a guaranteed value is a promise, and a limit is a boundary the contract can enforce.

Does the certificate belong to your cargo

• The lot or shipment reference matches the bill of lading, vessel name or container numbers.
• The sampling date fits the loading date.
• The quantity represented is consistent with the cargo.
• The issuer is a laboratory you can verify, and a quick call or email confirms the certificate number.
• Values differ plausibly between lots, not in identical figures to the second decimal on several different certificates.

Why results can differ

Two laboratories can report different results for the same material because of sampling, preparation or method differences. Contracts therefore state a procedure: for example, a split sample is retained, results are compared, and a defined umpire laboratory decides if the difference exceeds an agreed tolerance. Agree this procedure in advance so that a disagreement has a path to a final answer.

Pricing adjustments

Many contracts adjust the price for the assay result. A bonus may apply above a stated content, and penalties below it or for impurities. If you buy on analysis, write the adjustment table into the contract, with the units, steps and limits for rejection, so there is no argument about arithmetic later.

A quick reading routine

Tonport's document check can compare the main figures from an analysis certificate with the contract values, and it works in your browser.

• Header: who, when, which lot.
• Method: which standard, which basis.
• Main values against the specification, then the penalty elements.
• Moisture and physical properties.
• Signature, stamp and a contact for confirmation.

Questions fréquentes

What is the difference between an assay and a certificate of analysis?

In practice the words overlap. Assay usually refers to determining the content of a metal or valuable component, while certificate of analysis is a broader term for any laboratory report of measured properties.

Who should take the sample?

An independent party is preferred. The contract should say who samples, how, and whether a retained split sample is kept for later checks.

What does umpire laboratory mean?

It is a laboratory named in the contract to decide the result if the seller's and buyer's results differ by more than an agreed amount.

Can a certificate be issued before the cargo is loaded?

A certificate can describe a pre-shipment sample, but it should say so. Contracts often require a loading or discharge certificate in addition.