Quality-control testing is the analytical and physical testing carried out on a batch to confirm it meets its agreed specification before release - covering parameters such as concentration, purity, viscosity, pH, colour, or other product-specific measures depending on what matters for your formulation.
Key points
- Quality-control testing parameters should be explicitly agreed in your quality specification, not left to the manufacturer's general judgement.
- Testing methods and equipment vary by product - what's tested for a coating differs from what's tested for an agrochemical formulation.
- Results are typically documented in a certificate of analysis issued with each batch - see certificates of analysis.
- Testing discipline connects directly to batch traceability, since results need to be linked back to the specific batch and its raw materials.
What Good Practice Involves
A manufacturer with strong quality-control testing practice tests each batch against your agreed specification using appropriate, validated analytical methods, documents the results, and has a clear process for handling any batch that fails to meet specification rather than releasing it regardless.
Who It Applies To
Quality-control testing is primarily the manufacturer's operational responsibility, but the specific parameters, methods and acceptance criteria should be explicitly agreed between you and the manufacturer - see setting quality specifications.
What This Means for Contract Manufacturing
Agree your quality-control testing requirements explicitly before production begins, including which parameters are tested, what methods are used, and what happens if a batch fails - see quality agreements for how this is typically formalised.
Testing at Three Points
Quality control testing in chemical manufacturing normally happens at three stages, and it is worth being explicit about all three rather than only the last. Incoming materials are tested or verified against their specification before use. In-process checks during production confirm the batch is developing as expected, allowing correction while correction is still possible. Finished product testing establishes that the completed batch meets its release specification.
In-process testing is the stage buyers most often overlook and the one that prevents the most expensive failures. A pH or specific gravity check part-way through can catch a charging error while the batch can still be adjusted; the same error found at release means the whole batch is at risk.
Specification, Method and Frequency
A test requirement is not complete until three things are stated: the parameter and its limits, the method used to measure it, and how often it is tested. Different methods can give different results for the same property, so a specification that names a parameter without a method is not reliably testable and creates room for dispute about whether a batch conformed.
Frequency also needs agreeing. Testing every batch for every parameter is thorough and expensive; skip-lot or periodic testing of stable parameters is common practice and reasonable where justified. What matters is that the arrangement is deliberate and documented in the quality agreement rather than assumed.
Release, Deviation and Retesting
Agree in advance what happens when a result falls outside specification. A single out-of-specification result may reflect a genuine problem or a testing error, and the process for investigating that - rather than simply retesting until a passing result appears - is a meaningful indicator of a manufacturer's quality culture. Establish who decides whether a batch is released, on what basis, and what happens to material that fails. See certificates of analysis.
Where Testing Is Carried Out
Ask whether testing is done on site or sent to an external laboratory, since it affects lead time as much as confidence. On-site testing allows faster release and quicker in-process correction; external testing adds days to the cycle and can become the constraint on how quickly a batch reaches you. Where specialist analysis is subcontracted, it is reasonable to ask which laboratory is used and whether it is accredited.
Related Pages
Frequently Asked Questions
Who decides what quality-control tests are carried out?
This should be agreed jointly between you and the manufacturer, based on what parameters matter for your product's performance and any regulatory requirements - don't assume a manufacturer's standard testing automatically covers everything relevant to your formulation.
What happens if a batch fails quality-control testing?
This should be defined in your quality agreement in advance - typical outcomes include rework, rejection, or further investigation, but the specific process should be agreed rather than improvised after the fact.
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Search the DirectoryLast reviewed: August 2026. Regulation and guidance change — verify anything you rely on against the primary source. Tell us if something here is out of date.